详解Android XML中引用自定义内部类view的四个why

final Object[] mConstructorArgs = new Object[2];

  static final Class<?>[] mConstructorSignature = new Class[] {
      Context.class, AttributeSet.class};
      
  //...
  
  /**
   * Creates a view from a tag name using the supplied attribute set.
   * <p>
   * <strong>Note:</strong> Default visibility so the BridgeInflater can
   * override it.
   *
   * @param parent the parent view, used to inflate layout params
   * @param name the name of the XML tag used to define the view
   * @param context the inflation context for the view, typically the
   *        {@code parent} or base layout inflater context
   * @param attrs the attribute set for the XML tag used to define the view
   * @param ignoreThemeAttr {@code true} to ignore the {@code android:theme}
   *            attribute (if set) for the view being inflated,
   *            {@code false} otherwise
   */
  View createViewFromTag(View parent, String name, Context context, AttributeSet attrs,
      boolean ignoreThemeAttr) {
    //**关键1**//
    if (name.equals("view")) {
      name = attrs.getAttributeValue(null, "class");
    }

    // Apply a theme wrapper, if allowed and one is specified.
    if (!ignoreThemeAttr) {
      final TypedArray ta = context.obtainStyledAttributes(attrs, ATTRS_THEME);
      final int themeResId = ta.getResourceId(0, 0);
      if (themeResId != 0) {
        context = new ContextThemeWrapper(context, themeResId);
      }
      ta.recycle();
    }

    if (name.equals(TAG_1995)) {
      // Let's party like it's 1995!
      return new BlinkLayout(context, attrs);
    }

    try {
      View view;
      if (mFactory2 != null) {
        view = mFactory2.onCreateView(parent, name, context, attrs);
      } else if (mFactory != null) {
        view = mFactory.onCreateView(name, context, attrs);
      } else {
        view = null;
      }

      if (view == null && mPrivateFactory != null) {
        view = mPrivateFactory.onCreateView(parent, name, context, attrs);
      }

      if (view == null) {
        final Object lastContext = mConstructorArgs[0];
        mConstructorArgs[0] = context;
        try {
          if (-1 == name.indexOf('.')) {
            //**关键2**//
            view = onCreateView(parent, name, attrs);
          } else {
            //**关键3**//
            view = createView(name, null, attrs);
          }
        } finally {
          mConstructorArgs[0] = lastContext;
        }
      }

      return view;
    }
    //后面都是catch，省略
  }
  
  protected View onCreateView(View parent, String name, AttributeSet attrs)
      throws ClassNotFoundException {
    return onCreateView(name, attrs);
  }
  
  protected View onCreateView(String name, AttributeSet attrs)
      throws ClassNotFoundException {
    return createView(name, "android.view.", attrs);
  }
  
  /**
   * Low-level function for instantiating a view by name. This attempts to
   * instantiate a view class of the given <var>name</var> found in this
   * LayoutInflater's ClassLoader.
   * 
   * @param name The full name of the class to be instantiated.
   * @param attrs The XML attributes supplied for this instance.
   * 
   * @return View The newly instantiated view, or null.
   */
  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;

    try {
      Trace.traceBegin(Trace.TRACE_TAG_VIEW, name);

      if (constructor == null) {
        //**关键4**//
        // Class not found in the cache, see if it's real, and try to add it
        clazz = mContext.getClassLoader().loadClass(
            prefix != null ? (prefix + name) : name).asSubclass(View.class);
        
        if (mFilter != null && clazz != null) {
          boolean allowed = mFilter.onLoadClass(clazz);
          if (!allowed) {
            failNotAllowed(name, prefix, attrs);
          }
        }
        constructor = clazz.getConstructor(mConstructorSignature);
        constructor.setAccessible(true);
        sConstructorMap.put(name, constructor);
      } else {
        // If we have a filter, apply it to cached constructor
        if (mFilter != null) {
          // Have we seen this name before?
          Boolean allowedState = mFilterMap.get(name);
          if (allowedState == null) {
            // New class -- remember whether it is allowed
            clazz = mContext.getClassLoader().loadClass(
                prefix != null ? (prefix + name) : name).asSubclass(View.class);
            
            boolean allowed = clazz != null && mFilter.onLoadClass(clazz);
            mFilterMap.put(name, allowed);
            if (!allowed) {
              failNotAllowed(name, prefix, attrs);
            }
          } else if (allowedState.equals(Boolean.FALSE)) {
            failNotAllowed(name, prefix, attrs);
          }
        }
      }

      Object[] args = mConstructorArgs;
      args[1] = attrs;
      //**关键5**//
      final View view = constructor.newInstance(args);
      if (view instanceof ViewStub) {
        // Use the same context when inflating ViewStub later.
        final ViewStub viewStub = (ViewStub) view;
        viewStub.setLayoutInflater(cloneInContext((Context) args[0]));
      }
      return view;

    }
    //后面都是catch以及finally处理，省略
  }

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 { 
    //**关键6**//
    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); 
  } 

  //.........
}

static final Class<?>[] mConstructorSignature = new Class[] {Context.class, AttributeSet.class};