Android基础入门教程——7.5.1 WebView(网页视图)基本用法

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Android基础入门教程——7.5.1 WebView(网页视图)基本用法

标签（空格分隔）： Android基础入门教程

本节引言

本节给大家带来的是Android中的一个用于显示网页的控件：WebView(网页视图),现在Android应用
层开发的方向有两种：客户端开发和HTML5移动端开发！所谓的HTML5端就是：HTML5 + CSS + JS来构建
一个网页版的应用,而这中间的媒介就是这个WebView,而Web和网页端可以通过JS来进行交互,比如,
网页读取手机联系人,调用手机相关的API等！而且相比起普通的客户端开发,HTML5移动端有个优势：
可以用百分比来布局,而且如果HTML5端有什么大改,我们不用像客户端那样去重新下一个APP,然后
覆盖安装,我们只需修改下网页即可！而客户端…惨不忍睹,当然HTML5也有个缺点,就是性能的问题,
数据积累,耗电问题,还有闪屏等等…另外,针对这种跨平台我们可以使用其他的第三方快速开发
框架,比如PhoneGap,对了,还有现在网络上很多一键生成APP类的网站,用户通过拖拉,设置图片
之类的简单操作就可以生成一个应用,大部分都是用的HTML5来完成的！有模板,直接套,你懂的~
好的,话不多说,开始本节内容！

1.什么是WebView？

答：Android内置webkit内核的高性能浏览器,而WebView则是在这个基础上进行封装后的一个
控件,WebView直译网页视图,我们可以简单的看作一个可以嵌套到界面上的一个浏览器控件！

2.相关方法

先上官方文档：WebView
并不打算一个个地去讲属性,用到哪个写哪个,其他的自行查阅文档！
除了直接WebView外我们还可以添加你自己的行为,可以自行定制下述类：

WebChromeClient：辅助WebView处理Javascript的对话框、网站图标、网站title、加载进度等！
比如下面这些：

方法作用onJsAlert(WebView view,String url,String message,JsResult result)处理Js中的Alert对话框onJsConfirm(WebView view,String url,String message,JsResult result)处理Js中的Confirm对话框onJsPrompt(WebView view,String url,String message,String defaultValue,JsPromptResult result)处理Js中的Prompt对话框onProgressChanged(WebView view,int newProgress)当加载进度条发生改变时调用onReceivedIcon(WebView view, Bitmap icon)获得网页的icononReceivedTitle(WebView view, String title)获得网页的标题

WebViewClient：辅助WebView处理各种通知与请求事件！
比如下面这些方法：

方法作用onPageStared(WebView view,String url)通知主程序网页开始加载onPageFinished(WebView view,String url,Bitmap favicon)通知主程序,网页加载完毕doUpdateVisitedHistory(WebView view,String url,boolean isReload)更新历史记录onLoadResource(WebView view,String url)通知主程序WebView即将加载指定url的资源onScaleChanged(WebView view,float oldScale,float newScale)ViewView的缩放发生改变时调用shouldOverrideKeyEvent(WebView view,KeyEvent event)控制webView是否处理按键时间,如果返回true,则WebView不处理,返回false则处理shouldOverrideUrlLoading(WebView view,String url)控制对新加载的Url的处理,返回true,说明主程序处理WebView不做处理,返回false意味着WebView会对其进行处理onReceivedError(WebView view,int errorCode,String description,String failingUrl)遇到不可恢复的错误信息时调用

WebSettings：WebView相关配置的设置，比如setJavaScriptEnabled()设置是否允许JS脚本执行
部分方法如下：

方法作用getSettings()返回一个WebSettings对象,用来控制WebView的属性设置loadUrl(String url)加载指定的UrlloadData(String data,String mimeType,String encoding)加载指定的Data到WebView中.使用”data:”作为标记头,该方法不能加载网络数据.其中mimeType为数据类型如:textml,image/jpeg. encoding为字符的编码方式loadDataWithBaseURL(String baseUrl, String data, String mimeType, String encoding, String historyUrl)比上面的loadData更加强大setWebViewClient(WebViewClient client)为WebView指定一个WebViewClient对象.WebViewClient可以辅助WebView处理各种通知,请求等事件。setWebChromeClient(WebChromeClient client)为WebView指定一个WebChromeClient对象,WebChromeClient专门用来辅助WebView处理js的对话框,网站title,网站图标,加载进度条等

这里重要区分三个load方法的区别：

loadUrl()：直接显示网页内容(单独显示网络图片)，一般不会出现乱码。
loadData(data, “text/html”, “UTF-8”)：用来加载URI格式的数据，不能通过网络来加载内容，
不能加载图片，而且经常会遇到乱码的问题，我们知道String类型的数据主要是Unicode编码的，
而WebView一般为了节省资源使用的是UTF-8编码，尽管我们按上面写了，但是还需要为webView设置：
webview.getSettings().setDefaultTextEncodingName(“UTF -8”);
loadDataWithBaseURL(baseUrl, string, “text/html”, “utf-8”, null)：loadData类的一个
增强类，可以加载图片，baseUrl为你存储的图片路径，而且只需在这里设置utf-8就可以解决乱码
问题了！

这里只是列举了部分属性而已，其他的还需自行查阅官方文档：

WebChromeClient文档
WebViewClient文档
WebSettings文档

3.一些常见需求讲解

需求1：根据URL加载网页

1）直接在Activity上加载一个WebView

运行效果图：

实现代码：

<code class="language-Java hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">MainActivity</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">extends</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">AppCompatActivity</span> {</span>    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> WebView webView;    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">long</span> exitTime = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;    <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">protected</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onCreate</span>(Bundle savedInstanceState) {        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span>.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        webView = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> WebView(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>);        webView.setWebViewClient(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> WebViewClient() {            <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//设置在webView点击打开的新网页在当前界面显示,而不跳转到新的浏览器中</span>            <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> <span class="hljs-title" style="box-sizing: border-box;">shouldOverrideUrlLoading</span>(WebView view, String url) {                view.loadUrl(url);                <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>;            }        });        webView.getSettings().setJavaScriptEnabled(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>);  <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//设置WebView属性,运行执行js脚本</span>        webView.loadUrl(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"http://www.baidu.com/"</span>);          <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//调用loadView方法为WebView加入链接</span>        setContentView(webView);                           <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//调用Activity提供的setContentView将webView显示出来</span>    }    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//我们需要重写回退按钮的时间,当用户点击回退按钮：</span>    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//1.webView.canGoBack()判断网页是否能后退,可以则goback()</span>    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//2.如果不可以连续点击两次退出App,否则弹出提示Toast</span>    <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onBackPressed</span>() {        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (webView.canGoBack()) {            webView.goBack();        } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> ((System.currentTimeMillis() - exitTime) > <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2000</span>) {                Toast.makeText(getApplicationContext(), <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"再按一次退出程序"</span>,                        Toast.LENGTH_SHORT).show();                exitTime = System.currentTimeMillis();            } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {                <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span>.onBackPressed();            }        }    }}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li></ul>

2）布局代码中设置WebView

相信大家都见过很多的新闻类App吧或者门户信息类的App,他的结构可能是这样的：

左上角一个点击关闭当前Activity的按钮,中间是新闻的title,右面是一个刷新按钮,
而在右下角可能有这样一个悬浮的按钮,当我们滑动超过屏幕宽度他就会显示出来,
当用户点击后又会回滚到网页的顶部！下面我们来简单的实现下！

运行效果图：

实现代码：

MainActivity.java：

<code class="language-Java hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">MainActivity</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">extends</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">AppCompatActivity</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">implements</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">View</span>.<span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">OnClickListener</span> {</span>    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> Button btn_back;    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> TextView txt_title;    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> Button btn_top;    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> Button btn_refresh;    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> WebView wView;    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">long</span> exitTime = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;    <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">protected</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onCreate</span>(Bundle savedInstanceState) {        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span>.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        bindViews();    }    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">bindViews</span>() {        btn_back = (Button) findViewById(R.id.btn_back);        txt_title = (TextView) findViewById(R.id.txt_title);        btn_top = (Button) findViewById(R.id.btn_top);        btn_refresh = (Button) findViewById(R.id.btn_refresh);        wView = (WebView) findViewById(R.id.wView);        btn_back.setOnClickListener(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>);        btn_refresh.setOnClickListener(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>);        btn_top.setOnClickListener(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>);        wView.loadUrl(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"http://www.baidu.com"</span>);        wView.setWebChromeClient(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> WebChromeClient() {            <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//这里设置获取到的网站title</span>            <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onReceivedTitle</span>(WebView view, String title) {                <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span>.onReceivedTitle(view, title);                txt_title.setText(title);            }        });        wView.setWebViewClient(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> WebViewClient() {            <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//在webview里打开新链接</span>            <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> <span class="hljs-title" style="box-sizing: border-box;">shouldOverrideUrlLoading</span>(WebView view, String url) {                view.loadUrl(url);                <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>;            }        });    }    <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onClick</span>(View v) {        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">switch</span> (v.getId()) {            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">case</span> R.id.btn_back:                finish();          <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//关闭当前Activity</span>                <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>;            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">case</span> R.id.btn_refresh:                wView.reload();    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//刷新当前页面</span>                <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>;            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">case</span> R.id.btn_top:                wView.setScrollY(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>);   <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//滚动到顶部</span>                <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>;        }    }    <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onBackPressed</span>() {        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (wView.canGoBack()) {            wView.goBack();        } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> ((System.currentTimeMillis() - exitTime) > <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2000</span>) {                Toast.makeText(getApplicationContext(), <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"再按一次退出程序"</span>,                        Toast.LENGTH_SHORT).show();                exitTime = System.currentTimeMillis();            } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {                finish();            }        }    }}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li><li style="box-sizing: border-box; padding: 0px 5px;">60</li><li style="box-sizing: border-box; padding: 0px 5px;">61</li><li style="box-sizing: border-box; padding: 0px 5px;">62</li><li style="box-sizing: border-box; padding: 0px 5px;">63</li><li style="box-sizing: border-box; padding: 0px 5px;">64</li><li style="box-sizing: border-box; padding: 0px 5px;">65</li><li style="box-sizing: border-box; padding: 0px 5px;">66</li><li style="box-sizing: border-box; padding: 0px 5px;">67</li><li style="box-sizing: border-box; padding: 0px 5px;">68</li><li style="box-sizing: border-box; padding: 0px 5px;">69</li><li style="box-sizing: border-box; padding: 0px 5px;">70</li><li style="box-sizing: border-box; padding: 0px 5px;">71</li><li style="box-sizing: border-box; padding: 0px 5px;">72</li><li style="box-sizing: border-box; padding: 0px 5px;">73</li><li style="box-sizing: border-box; padding: 0px 5px;">74</li><li style="box-sizing: border-box; padding: 0px 5px;">75</li><li style="box-sizing: border-box; padding: 0px 5px;">76</li><li style="box-sizing: border-box; padding: 0px 5px;">77</li><li style="box-sizing: border-box; padding: 0px 5px;">78</li><li style="box-sizing: border-box; padding: 0px 5px;">79</li><li style="box-sizing: border-box; padding: 0px 5px;">80</li><li style="box-sizing: border-box; padding: 0px 5px;">81</li></ul>

问题答疑：
相信细心的朋友看到，我们回到一开始加载的页面后，按返回键，按了多次还是没有退出
当前的APP，后来还是我们手动去点back键通过调用finish方法才能关闭当前的Activity?
这是为什么呢？明明百度一下已经是第一个页面啊？

答：其实发生这个的原因是：网址的重定向问题引起的，其实我们在访问百度的时候：
尽管我们load的是www.baidu.com，但是百度做了重定向，跳转到了手机版百度一下网页：
即实际你的流程是：www.baidu.com -> 手机版百度一下 -> 打开其他的链接！
我们看到我们上面shouldOverrideUrlLoading()方法是这样写的：
view.loadUrl(url);return true;
我们知道用户点击一次回退键，那么webview会调用一次goback方法()，我们把上面三个
设做A,B,C三个站点，在C时点回退，C - > B没问题，接着再点 B -> A，这个时候问题
就来了尽管B来到了A，但是因为重定向又跳转到了B，如此循环往复…这就是为什么
点击回退键并没有推出WebView的原因，解决方法：手速，在webview未加载完网页
钱连续双击回退键，手速要够快，哈哈！说笑而已，要解决这个问题，我们只需将
shouldOverrideUrlLoading里的东东删掉，然后写上return false；即可！
不信是重定向，可以自己修改下URL试试~

需求2：WebView滚动事件的监听

我们都知道监听滚动事件一般都是设置setOnScrollChangedListener，可惜的是
WebView并没有给我们提供这样的方法，但是我们可以重写WebView，覆盖里面的一个方法：
protected void onScrollChanged(final int l, final int t, final int oldl,final int oldt){}
然后再对外提供一个接口，示例代码如下：

MyWebViewDemo.java：

<code class="language-Java hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/** * Created by Jay on 2015/9/11 0011. */</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">MyWebView</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">extends</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">WebView</span> {</span>    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> OnScrollChangedCallback mOnScrollChangedCallback;    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-title" style="box-sizing: border-box;">MyWebView</span>(Context context) {        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span>(context);    }    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-title" style="box-sizing: border-box;">MyWebView</span>(Context context, AttributeSet attrs) {        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span>(context, attrs);    }    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-title" style="box-sizing: border-box;">MyWebView</span>(Context context, AttributeSet attrs, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> defStyleAttr) {        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span>(context, attrs, defStyleAttr);    }    <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">protected</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onScrollChanged</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> l, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> t, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> oldl, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> oldt) {        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span>.onScrollChanged(l, t, oldl, oldt);        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (mOnScrollChangedCallback != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>) {            mOnScrollChangedCallback.onScroll(l - oldl, t - oldt);        }    }    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> OnScrollChangedCallback <span class="hljs-title" style="box-sizing: border-box;">getOnScrollChangedCallback</span>() {        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> mOnScrollChangedCallback;    }    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">setOnScrollChangedCallback</span>(            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> OnScrollChangedCallback onScrollChangedCallback) {        mOnScrollChangedCallback = onScrollChangedCallback;    }    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">interface</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">OnScrollChangedCallback</span> {</span>        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//这里的dx和dy代表的是x轴和y轴上的偏移量，你也可以自己把l, t, oldl, oldt四个参数暴露出来</span>        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onScroll</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> dx, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> dy);    }}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li></ul>

MainActivity.java:

<code class="language-Java hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">MainActivity</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">extends</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">AppCompatActivity</span> {</span>    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> MyWebView wView;    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> Button btn_icon;    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">long</span> exitTime = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;    <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">protected</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onCreate</span>(Bundle savedInstanceState) {        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span>.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        btn_icon = (Button) findViewById(R.id.btn_icon);        wView = (MyWebView) findViewById(R.id.wView);        wView.loadUrl(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"http://www.hao123.com"</span>);        wView.setWebViewClient(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> WebViewClient() {            <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//在webview里打开新链接</span>            <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> <span class="hljs-title" style="box-sizing: border-box;">shouldOverrideUrlLoading</span>(WebView view, String url) {                view.loadUrl(url);                <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>;            }        });        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//比如这里做一个简单的判断，当页面发生滚动，显示那个Button</span>        wView.setOnScrollChangedCallback(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> MyWebView.OnScrollChangedCallback() {            <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onScroll</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> dx, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> dy) {                <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (dy > <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>) {                    btn_icon.setVisibility(View.VISIBLE);                } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {                    btn_icon.setVisibility(View.GONE);                }            }        });        btn_icon.setOnClickListener(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> View.OnClickListener() {            <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onClick</span>(View v) {                wView.setScrollY(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>);                btn_icon.setVisibility(View.GONE);            }        });    }    <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onBackPressed</span>() {        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (wView.canGoBack()) {            wView.goBack();        } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> ((System.currentTimeMillis() - exitTime) > <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2000</span>) {                Toast.makeText(getApplicationContext(), <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"再按一次退出程序"</span>,                        Toast.LENGTH_SHORT).show();                exitTime = System.currentTimeMillis();            } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {                finish();            }        }    }}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li><li style="box-sizing: border-box; padding: 0px 5px;">60</li></ul>

运行效果图：

当网页开始滚动，会呈现一个呵呵的按钮，我们点击呵呵按钮可以回到顶部！
然后呵呵按钮会隐藏~

需求3：滚动条的问题

你可能用的属性如下：
setHorizontalScrollBarEnabled(false);//水平不显示
setVerticalScrollBarEnabled(false); //垂直不显示
setScrollBarStyle(View.SCROLLBARS_OUTSIDE_OVERLAY);//滚动条在WebView内侧显示
setScrollBarStyle(View.SCROLLBARS_INSIDE_OVERLAY)//滚动条在WebView外侧显示

需求4：设置缩放以及自适应屏幕

根据我们一般的习惯打开网页对于看不清楚的地方，我们喜欢双指来缩放网页，而WebView
则需要我们自己手动来设置这个是否支持缩放了！

只需要在加入下述代码即可：

<code class="language-Java hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">WebSettings settings = wView.getSettings();settings.setUseWideViewPort(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>);<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//设定支持viewport</span>settings.setLoadWithOverviewMode(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>);   <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//自适应屏幕</span>settings.setBuiltInZoomControls(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>);settings.setDisplayZoomControls(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>);settings.setSupportZoom(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>);<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//设定支持缩放</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li></ul>

使用上述代码后，进去页面就会是这样一个效果：

当我们缩放时，出现了一个恶心的问题，就是很常见的缩放控件，我们肯定是不想要的啦，
那么加上下面句代码就可以把缩放控件给隐藏掉了！

<code class="language-Java hljs bash has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">settings.setDisplayZoomControls(<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">false</span>);</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

我们也可以自行设置初始的缩放比例，只需为webView：

<code class="language-Java hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> wView.setInitialScale(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">25</span>);<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//为25%，最小缩放等级 </span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

嘿嘿，上面是整个网页都缩放的，不过可能有时我们仅仅是需要对字体进行缩放，那么可以
这样做：

<code class="language-Java hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">settings.setTextZoom(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span>)；</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

也可以直接通过：

<code class="language-Java hljs autohotkey has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">settings.setTextSize(TextSize.LARGER)；来设置大小Android自带五个可选字体大小的值：//SMALLEST(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">50</span><span class="hljs-var_expand" style="box-sizing: border-box;">%),SMALLER(75%</span>),NORMAL(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span><span class="hljs-var_expand" style="box-sizing: border-box;">%),LARGER(150%</span>), LARGEST(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">200</span><span class="hljs-var_expand" style="box-sizing: border-box;">%);</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul>

需求5.获取WebView的Cookie数据

我们都知道Cookie其实只是一个代表用户唯一标识的字符串，情景一般是：
用户输入账号密码后，点击登陆，用户要拿着这个Cookie去访问服务器提供的相关服务！
我们可以把cookie的获取写到onPageFinsihed的方法中，简单的可以这样写：

<code class="language-Java hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">     <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onPageFinished</span>(WebView view, String url) {                             CookieManager cookieManager = CookieManager.getInstance();                String CookieStr = cookieManager.getCookie(url);                Log.e(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"HEHE"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Cookies = "</span> + CookieStr);                <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span>.onPageFinished(view, url);            }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul>

需求6.设置WebView的Cookie数据

嘿嘿，我们上面获取到了Cookie或者通过其他途径获得了Cookie，我们如何为WebView设置Cookie呢？
我们可以在需要设置Cookie的地方加入下述代码：

<code class="language-Java hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">    CookieSyncManager<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.createInstance</span>(MainActivity<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.this</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;  </span>    CookieManager cookieManager = CookieManager<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.getInstance</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;  </span>    cookieManager<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.setAcceptCookie</span>(true)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;  </span>    cookieManager<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.setCookie</span>(url, cookies)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;  //cookies是要设置的cookie字符串 </span>    CookieSyncManager<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.getInstance</span>()<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.sync</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;  </span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul>

对了，上述代码需要写在loadUrl()之前，而且如果设置了Cookie了，尽量别再进行其他的设置
不然可能会无效，建议设置cookie的写在webView相关设置的最后面~loadUrl()之前!

4.示例代码下载：

WebViewDemo1：WebViewDemo1.zip
WebViewDemo2：WebViewDemo2.zip

本节小结：

好的，本节给大家介绍了一下WebView的基本用法，加载网页，设置缩放，字体缩放，
自适应屏幕，以及Cookie的获取以及设置；相信日常开发中还有各种奇葩的需求，不过
限于篇幅就写这么多，有idea的欢迎留言，下节我们来学习HTML5端如何通过JavaScript
来与WebView交互，并获取手机的相关数据！敬请期待~谢谢~

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