Handler初体验（一）——下载文件并更新进度条

来源：互联网发布：手机淘宝卖东西怎么弄编辑：程序博客网时间：2024/06/11 17:56

实现思路:

获取文件的输入流
把输入流读入到缓存流中，并累积记录流的长度
通过Handler机制将长度传递给UI线程
ProgressBar接到到读取长度以及文件总长度进行UI的更新。

界面效果:

这里写图片描述

布局代码:

<?xml version="1.0" encoding="utf-8"?><RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:paddingBottom="@dimen/activity_vertical_margin"    android:paddingLeft="@dimen/activity_horizontal_margin"    android:paddingRight="@dimen/activity_horizontal_margin"    android:paddingTop="@dimen/activity_vertical_margin"    tools:context="com.ycw.progresspro.MainActivity">    <Button        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="开始下载"        android:id="@+id/btn_start"        android:layout_alignParentBottom="true"        android:layout_alignParentRight="true"        android:layout_alignParentEnd="true"        android:layout_alignParentLeft="true"        android:layout_alignParentStart="true" />    <ProgressBar        style="?android:attr/progressBarStyleHorizontal"        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:id="@+id/progressBar"        android:max="100"        android:layout_alignParentTop="true"        android:layout_centerHorizontal="true" />    <TextView        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:textAppearance="?android:attr/textAppearanceLarge"        android:text="已下载"        android:id="@+id/textView"        android:layout_below="@+id/progressBar"        android:layout_alignParentLeft="true"        android:layout_alignParentStart="true" />    <TextView        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:textAppearance="?android:attr/textAppearanceLarge"        android:text="0%"        android:id="@+id/percent"        android:layout_below="@+id/progressBar"        android:layout_toRightOf="@+id/textView"        android:layout_toEndOf="@+id/textView" /></RelativeLayout>

添加权限:

<uses-permission android:name="android.permission.INTERNET"/><uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/><uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>

PS：如果运行环境API>23的话（Android6.0及之后），需要动态申请权限，详情可以查看我的另一篇博客关于Android6.0读写文件权限问题

实现代码:

代码里面有非常详细的注释

public class MainActivity extends AppCompatActivity {    private static final int DOWNLOAD_FILE_CODE = 100001 ;    private static final String DOWNLOAD_URL ="http://download.sj.qq.com/upload/connAssitantDownload/upload/MobileAssistant_1.apk" ;    private static final int DOWNLOAD_FILE_FAILE_CODE = 100002;    private Button StartDownload;    private TextView percent;    private ProgressBar progressBar;    private Handler handler;    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        initView();        StartDownload.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                //执行下载程序                new Thread(new Runnable() {                    @Override                    public void run() {                        download(DOWNLOAD_URL);                    }                }).start();            }        });        handler = new Handler(){            @Override            public void handleMessage(Message msg) {                super.handleMessage(msg);                switch (msg.what){                    case 100001:                        //更新进度条                        progressBar.setProgress((Integer) msg.obj);                        percent.setText(String.valueOf(msg.arg1)+"%");                        if (progressBar.getProgress()==100){                            Toast.makeText(MainActivity.this, "下载完成", Toast.LENGTH_SHORT).show();                        }                        break;                    case 100002:                        Toast.makeText(MainActivity.this, "下载失败", Toast.LENGTH_SHORT).show();                        break;                }            }        };    }    private void download(String AppUrl) {        //实例化URL对象        try {            URL url = new URL(AppUrl);            //实例化一个URLConnection对象            URLConnection conn = url.openConnection();            //获取下载路径            String path = Environment.getExternalStorageDirectory()                    + File.separator + "ZerGen" + File.separator;            //创建目录            File PathName = new File(path);            //如果PathName不存在的话 就创建这个目录            if(!PathName.exists()){                PathName.mkdir();            }            //有了目录之后，就需要一个文件名            String ApkName = path+"ZerGen.apk";            //判断一下这个文件是否已经存在，存在的话就删除它            File ApkFile = new File(ApkName);            if(ApkFile.exists()){                ApkFile.delete();            }            //获取文件的总长度            int ContentLength = conn.getContentLength();            //获取输入流            InputStream in = conn.getInputStream();            byte[] b = new byte[1024];            int DownloadLength = 0; //用于保存实时下载长度            int len  =0;            OutputStream out = new FileOutputStream(ApkName);            while((len = in.read(b))>-1){                 out.write(b,0,len);                 DownloadLength += len;                //将实时的下载长度传给UI线程                Message message=handler.obtainMessage();                message.what =DOWNLOAD_FILE_CODE;                message.obj = DownloadLength*100/ContentLength;                message.arg1 = DownloadLength*100/ContentLength;                handler.sendMessage(message);            }        } catch (java.io.IOException e) {            downloadfail();            e.printStackTrace();        }    }    private void downloadfail() {        Message message=handler.obtainMessage();        message.what =DOWNLOAD_FILE_FAILE_CODE;        handler.sendMessage(message);    }    private void initView() {        StartDownload = (Button) findViewById(R.id.btn_start);        percent = (TextView) findViewById(R.id.percent);        progressBar = (ProgressBar) findViewById(R.id.progressBar);    }}

最终效果:

这里写图片描述

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