Android LayoutInflater源码分析及使用(二)
来源:互联网 发布:数据误删恢复软件 编辑:程序博客网 时间:2024/05/20 01:45
上一篇中我们简单介绍了LayoutInflater是怎么获取的,那么这一篇我们将详细介绍他的一个我们最常用的方法inflate,流程是这样的,我们先进行源码分析,然后猜想,最后在具体验证。在介绍inflate方法之前我们先看下面这几行代码,
* <p>* For performance reasons, view inflation relies heavily on pre-processing of* XML files that is done at build time. Therefore, it is not currently possible* to use LayoutInflater with an XmlPullParser over a plain XML file at runtime;* it only works with an XmlPullParser returned from a compiled resource* (R.<em>something</em> file.)* * @see Context#getSystemService*/public abstract class LayoutInflater {………………………… private static final String TAG_MERGE = "merge"; private static final String TAG_INCLUDE = "include"; private static final String TAG_1995 = "blink"; private static final String TAG_REQUEST_FOCUS = "requestFocus";除了TAG_1995这个属性我们可能用的比较少以外,其他的我们应该都用过,如果标签为TAG_1995的话,我们初始化的是BlinkLayout这个类,我们通过源码可以看一下其实他就是个FrameLayout
private static class BlinkLayout extends FrameLayout { private static final int MESSAGE_BLINK = 0x42; private static final int BLINK_DELAY = 500; private boolean mBlink; private boolean mBlinkState; private final Handler mHandler;由于这个平时用的比较少,我们这里就不在介绍,我们主要看一下其他的三个属性,TAG_MERGE 属性我们一般自定义控件的时候为了减少层级用的表较多一些,TAG_INCLUDE 属性主要是为了减少代码复用,TAG_REQUEST_FOCUS 主要在EditText中为了获取焦点的时候用到。好了,上面只是一个简单的开头,下面我们就来详细分析inflate这个方法,以下是源码
/** * Inflate a new view hierarchy from the specified xml resource. Throws * {@link InflateException} if there is an error. * * @param resource ID for an XML layout resource to load (e.g., * <code>R.layout.main_page</code>) * @param root Optional view to be the parent of the generated hierarchy. * @return The root View of the inflated hierarchy. If root was supplied, * this is the root View; otherwise it is the root of the inflated * XML file. */ public View inflate(int resource, ViewGroup root) { return inflate(resource, root, root != null); }我们看他的另一个重构的方法
public View inflate(int resource, ViewGroup root, boolean attachToRoot) { if (DEBUG) System.out.println("INFLATING from resource: " + resource); XmlResourceParser parser = getContext().getResources().getLayout(resource); try { return inflate(parser, root, attachToRoot); } finally { parser.close(); } }他首先通过parser解析得到XmlResourceParser对象,
public XmlResourceParser getLayout(int id) throws NotFoundException { return loadXmlResourceParser(id, "layout"); }
具体怎么解析的,大家可以看他的源码,这里就不在介绍,我们主要来看一看inflate这个方法的实现,他是我们主要分析的对象,下面是全部源码,都没有任何删除,并且还加了注释,其中他里面还有一些调用的方法,这个不作为我们重点分析的对象,待会我们简单提一下就行了,有兴趣的大家可以自己去分析
/** * Inflate a new view hierarchy from the specified XML node. Throws * {@link InflateException} if there is an error. * <p> * <em><strong>Important</strong></em> For performance * reasons, view inflation relies heavily on pre-processing of XML files * that is done at build time. Therefore, it is not currently possible to * use LayoutInflater with an XmlPullParser over a plain XML file at runtime. * * @param parser XML dom node containing the description of the view * hierarchy. * @param root Optional view to be the parent of the generated hierarchy (if * <em>attachToRoot</em> is true), or else simply an object that * provides a set of LayoutParams values for root of the returned * hierarchy (if <em>attachToRoot</em> is false.) * @param attachToRoot Whether the inflated hierarchy should be attached to * the root parameter? If false, root is only used to create the * correct subclass of LayoutParams for the root view in the XML. * @return The root View of the inflated hierarchy. If root was supplied and * attachToRoot is true, this is root; otherwise it is the root of * the inflated XML file. */ public View inflate(XmlPullParser parser, ViewGroup root, boolean attachToRoot) { synchronized (mConstructorArgs) { Trace.traceBegin(Trace.TRACE_TAG_VIEW, "inflate"); final AttributeSet attrs = Xml.asAttributeSet(parser); /*mConstructorArgs是一个长度为2的数组,第一个存放的是Context,第二个存放的是attrs,主要在 * createView中用到*/ Context lastContext = (Context)mConstructorArgs[0]; mConstructorArgs[0] = mContext; View result = root; try { // Look for the root node. int type; /*不停循环,直到找到开始的标签位置*/ while ((type = parser.next()) != XmlPullParser.START_TAG && type != XmlPullParser.END_DOCUMENT) { // Empty } /*没找到则抛出异常*/ if (type != XmlPullParser.START_TAG) { throw new InflateException(parser.getPositionDescription() + ": No start tag found!"); } final String name = parser.getName(); if (DEBUG) { System.out.println("**************************"); System.out.println("Creating root view: " + name); System.out.println("**************************"); } /*(1)这个标签我们一般自定义控件的时候用的比较多,就是说<merge/>必须要有一个父控件, * 否则就会抛出异常,待会我们给大家演示一下,这先标记为我们的第一个问题*/ if (TAG_MERGE.equals(name)) { if (root == null || !attachToRoot) { throw new InflateException("<merge /> can be used only with a valid " + "ViewGroup root and attachToRoot=true"); } /*(2)rInflate方法主要是把parser解析出来的标签和attrs属性共同创建的View * 添加到父控件root中,待会我们在具体分析*/ rInflate(parser, root, attrs, false); } else { // Temp is the root view that was found in the xml View temp; if (TAG_1995.equals(name)) { /*这个我们上面说了,他其实就是继承的FrameLayout,相当于new了一个FrameLayout*/ temp = new BlinkLayout(mContext, attrs); } else { /*(3)这个方法根据名字大家可能也能猜出来就是根据name来创建View,事实证明我们 * 的猜测是正确的,不过这回他不是new出来一个View,他是通过类name和attrs, * 然后由loadClass加载这个类,最后newInstance这个View*/ temp = createViewFromTag(root, name, attrs); } ViewGroup.LayoutParams params = null; if (root != null) { if (DEBUG) { System.out.println("Creating params from root: " + root); } // Create layout params that match root, if supplied /*(4)如果root不为空,获取根布局的宽和高属性,*/ params = root.generateLayoutParams(attrs); if (!attachToRoot) { // Set the layout params for temp if we are not // attaching. (If we are, we use addView, below) /*(5)如果root不为空,且attachToRoot为false,把根布局的长和宽设置 * 给创建的temp View,其实我们根据他的注释大概也能猜测如果没有attach, * 这把上面获得的参数params给我们创建的temp,如果attach则在下面把它给add进去*/ temp.setLayoutParams(params); } } if (DEBUG) { System.out.println("-----> start inflating children"); } // Inflate all children under temp /*这个同上面的问题(2),我们待会再讲*/ rInflate(parser, temp, attrs, true); if (DEBUG) { System.out.println("-----> done inflating children"); } // We are supposed to attach all the views we found (int temp) // to root. Do that now. if (root != null && attachToRoot) { /*把我们创建的temp add到root中*/ root.addView(temp, params); } // Decide whether to return the root that was passed in or the // top view found in xml. if (root == null || !attachToRoot) { /*没有把temp add到temp中*/ result = temp; } } } catch (XmlPullParserException e) { InflateException ex = new InflateException(e.getMessage()); ex.initCause(e); throw ex; } catch (IOException e) { InflateException ex = new InflateException( parser.getPositionDescription() + ": " + e.getMessage()); ex.initCause(e); throw ex; } finally { // Don't retain static reference on context. /*最后把数组的第一个context设置为lastContext,然后第二个attrs设置为空*/ mConstructorArgs[0] = lastContext; mConstructorArgs[1] = null; } Trace.traceEnd(Trace.TRACE_TAG_VIEW); return result; } }不要急,等我们把所有问题全部分析完成之后再做最后的猜想和验证,我们先来看上面第二个问题的源码
/** * Recursive method used to descend down the xml hierarchy and instantiate * views, instantiate their children, and then call onFinishInflate(). */ void rInflate(XmlPullParser parser, View parent, final AttributeSet attrs, boolean finishInflate) throws XmlPullParserException, IOException { final int depth = parser.getDepth(); int type; while (((type = parser.next()) != XmlPullParser.END_TAG || parser.getDepth() > depth) && type != XmlPullParser.END_DOCUMENT) { if (type != XmlPullParser.START_TAG) { continue; } final String name = parser.getName(); if (TAG_REQUEST_FOCUS.equals(name)) { parseRequestFocus(parser, parent); } else if (TAG_INCLUDE.equals(name)) { if (parser.getDepth() == 0) { throw new InflateException("<include /> cannot be the root element"); } parseInclude(parser, parent, attrs); } else if (TAG_MERGE.equals(name)) { throw new InflateException("<merge /> must be the root element"); } else if (TAG_1995.equals(name)) { final View view = new BlinkLayout(mContext, attrs); final ViewGroup viewGroup = (ViewGroup) parent; final ViewGroup.LayoutParams params = viewGroup.generateLayoutParams(attrs); rInflate(parser, view, attrs, true); viewGroup.addView(view, params); } else { final View view = createViewFromTag(parent, name, attrs); final ViewGroup viewGroup = (ViewGroup) parent; final ViewGroup.LayoutParams params = viewGroup.generateLayoutParams(attrs); rInflate(parser, view, attrs, true); viewGroup.addView(view, params); } } if (finishInflate) parent.onFinishInflate(); }通过源码我们可以看出如果有<merge />标签,那么他必须为第一个,否则会抛出异常。最后根据是否加载完成来调用onFinishInflate方法,这个方法有时候也是我们在自定义控件的时候常用到的。如果标签为TAG_REQUEST_FOCUS,那么他的代码很简单,主要就这一行parent.requestFocus();,源码就不在贴出,如果标签为TAG_INCLUDE就会调用下面方法
private void parseInclude(XmlPullParser parser, View parent, AttributeSet attrs) throws XmlPullParserException, IOException { int type; if (parent instanceof ViewGroup) { final int layout = attrs.getAttributeResourceValue(null, "layout", 0); if (layout == 0) { final String value = attrs.getAttributeValue(null, "layout"); if (value == null) { throw new InflateException("You must specifiy a layout in the" + " include tag: <include layout=\"@layout/layoutID\" />"); } else { throw new InflateException("You must specifiy a valid layout " + "reference. The layout ID " + value + " is not valid."); } } else { final XmlResourceParser childParser = getContext().getResources().getLayout(layout); try { final AttributeSet childAttrs = Xml.asAttributeSet(childParser); while ((type = childParser.next()) != XmlPullParser.START_TAG && type != XmlPullParser.END_DOCUMENT) { // Empty. } if (type != XmlPullParser.START_TAG) { throw new InflateException(childParser.getPositionDescription() + ": No start tag found!"); } final String childName = childParser.getName(); if (TAG_MERGE.equals(childName)) { // Inflate all children. rInflate(childParser, parent, childAttrs, false); } else { final View view = createViewFromTag(parent, childName, childAttrs); final ViewGroup group = (ViewGroup) parent; // We try to load the layout params set in the <include /> tag. If // they don't exist, we will rely on the layout params set in the // included XML file. // During a layoutparams generation, a runtime exception is thrown // if either layout_width or layout_height is missing. We catch // this exception and set localParams accordingly: true means we // successfully loaded layout params from the <include /> tag, // false means we need to rely on the included layout params. ViewGroup.LayoutParams params = null; try { params = group.generateLayoutParams(attrs); } catch (RuntimeException e) { params = group.generateLayoutParams(childAttrs); } finally { if (params != null) { view.setLayoutParams(params); } } // Inflate all children. rInflate(childParser, view, childAttrs, true); // Attempt to override the included layout's android:id with the // one set on the <include /> tag itself. TypedArray a = mContext.obtainStyledAttributes(attrs, com.android.internal.R.styleable.View, 0, 0); int id = a.getResourceId(com.android.internal.R.styleable.View_id, View.NO_ID); // While we're at it, let's try to override android:visibility. int visibility = a.getInt(com.android.internal.R.styleable.View_visibility, -1); a.recycle(); if (id != View.NO_ID) { view.setId(id); } switch (visibility) { case 0: view.setVisibility(View.VISIBLE); break; case 1: view.setVisibility(View.INVISIBLE); break; case 2: view.setVisibility(View.GONE); break; } group.addView(view); } } finally { childParser.close(); } } } else { throw new InflateException("<include /> can only be used inside of a ViewGroup"); } final int currentDepth = parser.getDepth(); while (((type = parser.next()) != XmlPullParser.END_TAG || parser.getDepth() > currentDepth) && type != XmlPullParser.END_DOCUMENT) { // Empty } }其实原理和上面差不多,我们就不在一一分析,我们主要来看一下这里面的一个方法createViewFromTag,也是在上面我们提到的问题(3),他的源码如下,我们仔细看
/* * default visibility so the BridgeInflater can override it. */ View createViewFromTag(View parent, String name, AttributeSet attrs) { if (name.equals("view")) { name = attrs.getAttributeValue(null, "class"); } if (DEBUG) System.out.println("******** Creating view: " + name); try { View view; if (mFactory2 != null) view = mFactory2.onCreateView(parent, name, mContext, attrs); else if (mFactory != null) view = mFactory.onCreateView(name, mContext, attrs); else view = null; if (view == null && mPrivateFactory != null) { view = mPrivateFactory.onCreateView(parent, name, mContext, attrs); } if (view == null) { if (-1 == name.indexOf('.')) { /*(1)*/ view = onCreateView(parent, name, attrs); } else { /*(2)*/ view = createView(name, null, attrs); } } if (DEBUG) System.out.println("Created view is: " + view); return view; } catch (InflateException e) { throw e; } catch (ClassNotFoundException e) { InflateException ie = new InflateException(attrs.getPositionDescription() + ": Error inflating class " + name); ie.initCause(e); throw ie; } catch (Exception e) { InflateException ie = new InflateException(attrs.getPositionDescription() + ": Error inflating class " + name); ie.initCause(e); throw ie; } }最上面的Factory其实就是个接口,我们主要看我标注的(1)和(2)两部分,其实最终还是(1)调用了(2),我们看源码
protected View onCreateView(View parent, String name, AttributeSet attrs) throws ClassNotFoundException { return onCreateView(name, attrs); }接着看
protected View onCreateView(String name, AttributeSet attrs) throws ClassNotFoundException { return createView(name, "android.view.", attrs); }我们看到了在第二个参数传入的是"android.view.",回想我们上一篇讲的怎么获取LayoutInflater的时候,说到其实我们获取的是PhoneLayoutInflater,我们在PhoneLayoutInflater中看到这样几行代码,代码如下,已经略去一部分
public class PhoneLayoutInflater extends LayoutInflater { private static final String[] sClassPrefixList = { "android.widget.", "android.webkit.", "android.app." }; ……………………………… /** Override onCreateView to instantiate names that correspond to the widgets known to the Widget factory. If we don't find a match, call through to our super class. */ @Override protected View onCreateView(String name, AttributeSet attrs) throws ClassNotFoundException { for (String prefix : sClassPrefixList) { try { View view = createView(name, prefix, attrs); if (view != null) { return view; } } catch (ClassNotFoundException e) { // In this case we want to let the base class take a crack // at it. } } return super.onCreateView(name, attrs); }看懂了吧,其实他就是传入的包名加一个点,目的就是拼接一个完整的控件路径然后在初始化,我们看源码
public final View createView(String name, String prefix, AttributeSet attrs) throws ClassNotFoundException, InflateException { Constructor<? extends View> constructor = sConstructorMap.get(name); Class<? extends View> clazz = null; ………………………… if (constructor == null) { // 如果prefix为null说明name是个完整的路径 clazz = mContext.getClassLoader().loadClass( prefix != null ? (prefix + name) : name).asSubclass(View.class); ………………………… constructor = clazz.getConstructor(mConstructorSignature); sConstructorMap.put(name, constructor); } else { ………………………… clazz = mContext.getClassLoader().loadClass( prefix != null ? (prefix + name) : name).asSubclass(View.class); ………………………… } /*这就是上面inflate方法中我们提到的长度为2的一个数组,通过下面的newInstance创建一个新的View*/ Object[] args = mConstructorArgs; args[1] = attrs; final View view = constructor.newInstance(args); ………………………… return view; ………………………… }接着我们分析上面(4)个问题的源码,这个比较简单
public LayoutParams generateLayoutParams(AttributeSet attrs) { return new LayoutParams(getContext(), attrs); }我们继续
public LayoutParams(Context c, AttributeSet attrs) { TypedArray a = c.obtainStyledAttributes(attrs, R.styleable.ViewGroup_Layout); setBaseAttributes(a, R.styleable.ViewGroup_Layout_layout_width, R.styleable.ViewGroup_Layout_layout_height); a.recycle(); }我们在来看一看setBaseAttributes的源码
protected void setBaseAttributes(TypedArray a, int widthAttr, int heightAttr) { width = a.getLayoutDimension(widthAttr, "layout_width"); height = a.getLayoutDimension(heightAttr, "layout_height"); }看到了吧,就是设置LayoutParams参数的宽和高。其实无论是new一个View还是newInstance一个View,那么AttributeSet属性并不能设置View的宽和高,因为我们知道View的宽高是由ViewRootImpl的performTraversals方法最先调用,然后再由自身的Measure方法和LayoutParams参数测量之后共同决定的,待会给大家总结的时候,可能就会明白为什么View的背景和其他属性都起作用,但设置宽和高却没有任何作用,原因就在这
好了,到目前为止我们把LayoutInflater及它的inflate方法都分析完了,那么下面我们就猜想,然后在验证上面遗留的一些问题,猜想如下
public View inflate(int resource, ViewGroup root, boolean attachToRoot)
为了便于大家理解,我们来定义两个术语,根布局和root,意思虽然差不多,但所指却截然不同,根布局就是指我们自定义layout的根View,root是指我们inflate的那个类
(1)如果merge为根布局root不能为空,否则抛异常
(以下3个问题是在没有merge的情况下讨论)
(2)如果root为空,attachToRoot无论是true或false都没有任何意义,root与他没有任何关系,但根布局的属性保留了下来,宽高没有保留,(因为上面我们分析的createViewFromTag方法在创建temp的时候只是把attrs传了过去,通过newInstance创建了View对象,但并没有把LayoutParams设置进去,所以宽高并没有任何作用)
(3)如果root不为空,且attachToRoot为true,则根布局的所有属性都会保留下来,包括宽高,并且root还是布局文件的父类(通过源码我们可以看到 if (root != null && attachToRoot)则root.addView(temp, params),就是把temp和参数全部设置进去)
(4)如果root不为空,且attachToRoot为false,则根布局的所有属性和宽高都会保留下来,但不会add到root中,所以root也不会是布局文件的父类(我们通过最上面代码中的问题5可以看到,就是把LayoutParams设置进去了,但没有add)
好了,到目前为止,LayoutInflater及它的inflate方法我们都分析完了,那么究竟对不对,在下一篇中我们将举例为大家验证。
- Android LayoutInflater源码分析及使用(二)
- Android LayoutInflater源码分析及使用(一)
- Android LayoutInflater源码分析及使用(三)
- Android LayoutInflater.inflate的使用及源码分析
- Android LayoutInflater 源码分析及个人总结
- Weevely使用及源码分析(二)
- LayoutInflater效率分析及源码跟踪
- LayoutInflater.inflater()方法及参数源码分析
- Android LayoutInflater作用及使用
- LayoutInflater作用及使用(Android)
- Android------LayoutInflater作用及使用
- Android------LayoutInflater作用及使用
- Android LayoutInflater了解及使用
- Android View 源码 分析 之 LayoutInFlater
- Android面试题-LayoutInflater源码分析
- 读书笔记(二)---看看LayoutInflater的源码
- LayoutInflater源码分析
- LayoutInflater源码分析
- 面试感悟
- Android 中的XML 解析方法Pull 和Sax
- easyui的treegrid开发使用
- Razor 标签语法(1-11) Label,Text,Hidden,Password,Radio,CheckBox,DropdownList,Href,Img,Css,JS
- http请求
- Android LayoutInflater源码分析及使用(二)
- 字符串反转
- Struts2+Jquery实现ajax并返回json类型数据
- 算法_动态规划_图像压缩
- declaration(声明)与definition(定义)
- 1.PHP 预定义接口 --- ArrayAccess(数组式访问)接口
- 使用markdown
- HDU 4585 平衡树Treap
- 运用cocoaPods 在项目中找不到头文件的解决办法