Android XML中引用自定义内部类view的四个why，androidxml

Android XML中引用自定义内部类view的四个why，androidxml

　　今天碰到了在XML中应用以内部类形式定义的自定义view，结果遇到了一些坑。虽然通过看了一些前辈写的文章解决了这个问题，但是我看到的几篇都没有完整说清楚why，于是决定做这个总结。

使用自定义内部类view的规则

　　本文主要是总结why，所以先把XML布局文件中引用内部类的自定义view的做法摆出来，有四点：

布局加载流程主要代码　　

　　首先，XML布局文件的加载都是使用LayoutInflater来实现的，通过这篇文章的分析，我们知道实际使用的LayoutInflater类是其子类PhoneLayoutInflater，然后通过这篇文章的分析，我们知道view的真正实例化的关键入口函数是createViewFromTag这个函数，然后通过createView来真正实例化view，下面便是该流程用到的关键函数的主要代码：

  1     final Object[] mConstructorArgs = new Object[2];
  2 
  3     static final Class<?>[] mConstructorSignature = new Class[] {
  4             Context.class, AttributeSet.class};
  5             
  6     //...
  7     
  8     /**
  9      * Creates a view from a tag name using the supplied attribute set.
 10      * <p>
 11      * <strong>Note:</strong> Default visibility so the BridgeInflater can
 12      * override it.
 13      *
 14      * @param parent the parent view, used to inflate layout params
 15      * @param name the name of the XML tag used to define the view
 16      * @param context the inflation context for the view, typically the
 17      *                {@code parent} or base layout inflater context
 18      * @param attrs the attribute set for the XML tag used to define the view
 19      * @param ignoreThemeAttr {@code true} to ignore the {@code android:theme}
 20      *                        attribute (if set) for the view being inflated,
 21      *                        {@code false} otherwise
 22      */
 23     View createViewFromTag(View parent, String name, Context context, AttributeSet attrs,
 24             boolean ignoreThemeAttr) {
 25         //**关键1**//
 26         if (name.equals("view")) {
 27             name = attrs.getAttributeValue(null, "class");
 28         }
 29 
 30         // Apply a theme wrapper, if allowed and one is specified.
 31         if (!ignoreThemeAttr) {
 32             final TypedArray ta = context.obtainStyledAttributes(attrs, ATTRS_THEME);
 33             final int themeResId = ta.getResourceId(0, 0);
 34             if (themeResId != 0) {
 35                 context = new ContextThemeWrapper(context, themeResId);
 36             }
 37             ta.recycle();
 38         }
 39 
 40         if (name.equals(TAG_1995)) {
 41             // Let's party like it's 1995!
 42             return new BlinkLayout(context, attrs);
 43         }
 44 
 45         try {
 46             View view;
 47             if (mFactory2 != null) {
 48                 view = mFactory2.onCreateView(parent, name, context, attrs);
 49             } else if (mFactory != null) {
 50                 view = mFactory.onCreateView(name, context, attrs);
 51             } else {
 52                 view = null;
 53             }
 54 
 55             if (view == null && mPrivateFactory != null) {
 56                 view = mPrivateFactory.onCreateView(parent, name, context, attrs);
 57             }
 58 
 59             if (view == null) {
 60                 final Object lastContext = mConstructorArgs[0];
 61                 mConstructorArgs[0] = context;
 62                 try {
 63                     if (-1 == name.indexOf('.')) {
 64                         //**关键2**//
 65                         view = onCreateView(parent, name, attrs);
 66                     } else {
 67                         //**关键3**//
 68                         view = createView(name, null, attrs);
 69                     }
 70                 } finally {
 71                     mConstructorArgs[0] = lastContext;
 72                 }
 73             }
 74 
 75             return view;
 76         }
 77         //后面都是catch，省略
 78     }
 79     
 80     protected View onCreateView(View parent, String name, AttributeSet attrs)
 81             throws ClassNotFoundException {
 82         return onCreateView(name, attrs);
 83     }
 84     
 85     protected View onCreateView(String name, AttributeSet attrs)
 86             throws ClassNotFoundException {
 87         return createView(name, "android.view.", attrs);
 88     }
 89     
 90     /**
 91      * Low-level function for instantiating a view by name. This attempts to
 92      * instantiate a view class of the given <var>name</var> found in this
 93      * LayoutInflater's ClassLoader.
 94      * 
 95