Android布局加载之LayoutInflater示例详解

  registerService(Context.LAYOUT_INFLATER_SERVICE, LayoutInflater.class,
    new CachedServiceFetcher<LayoutInflater>() {
   @Override
   public LayoutInflater createService(ContextImpl ctx) {
    return new PhoneLayoutInflater(ctx.getOuterContext());
   }});

View inflate(@LayoutRes int resource, @Nullable ViewGroup root)
View inflate(@LayoutRes int resource, @Nullable ViewGroup root, boolean attachToRoot)

     // temp 是 xml 布局中的顶层 View
     final View temp = createViewFromTag(root, name, inflaterContext, attrs);
     ViewGroup.LayoutParams params = null;
     if (root != null) { // root 
      // root 不为 null 才会生成 layoutParams
      params = root.generateLayoutParams(attrs);
      if (!attachToRoot) {
       // 如果不添加到 root 中，则直接把布局参数设置给 temp
       temp.setLayoutParams(params);
      }
     }
     // 加载子 View 
     rInflateChildren(parser, temp, attrs, true);
     if (root != null && attachToRoot) {
      root.addView(temp, params);//添加到布局中，则布局参数用到 addView 中去
     }
     if (root == null || !attachToRoot) {
      result = temp;
     }

   View view; // 最后要返回的 View
   if (mFactory2 != null) {
    view = mFactory2.onCreateView(parent, name, context, attrs); // 是否设置了 Factory2 
   } else if (mFactory != null) {
    view = mFactory.onCreateView(name, context, attrs); // 是否设置了 Factory
   } else {
    view = null;
   }
   if (view == null && mPrivateFactory != null) { // 是否设置了 PrivateFactory
    view = mPrivateFactory.onCreateView(parent, name, context, attrs);
   }
   if (view == null) { // 如果的 Factory 都没有设置过，最后在生成 View
    final Object lastContext = mConstructorArgs[0];
    mConstructorArgs[0] = context;
    try {
     if (-1 == name.indexOf('.')) { // 系统控件 
      view = onCreateView(parent, name, attrs);
     } else { // 非系统控件，自定义的 View 
      view = createView(name, null, attrs);
     }
    } finally {
     mConstructorArgs[0] = lastContext;
    }
   }

// 通过反射生成 View 的参数，分别是 Context 和 AttributeSet 类
static final Class<?>[] mConstructorSignature = new Class[] {
   Context.class, AttributeSet.class};
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) { // 从缓存中得到 View 的构造器，没有则调用 getConstructor
    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) { // 过滤，是否允许生成该 View
     // 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); // 不允许生成该 View
     }
    }
   }
  Object[] args = mConstructorArgs;
  args[1] = attrs;
  final View view = constructor.newInstance(args); // 通过反射生成 View
  return view;

void rInflate(XmlPullParser parser, View parent, Context context,
   AttributeSet attrs, boolean finishInflate) throws XmlPullParserException, IOException {
  final int depth = parser.getDepth();
  int type;
  // 若 while 条件不成立，则加载结束了
  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(); // 从 XmlPullParser 中得到 name 出来解析
   if (TAG_REQUEST_FOCUS.equals(name)) { // name 各种情况下的解析
    parseRequestFocus(parser, parent);
   } else if (TAG_TAG.equals(name)) {
    parseViewTag(parser, parent, attrs);
   } else if (TAG_INCLUDE.equals(name)) {
    if (parser.getDepth() == 0) {
     throw new InflateException("<include /> cannot be the root element");
    }
    parseInclude(parser, context, parent, attrs);
   } else if (TAG_MERGE.equals(name)) {
    throw new InflateException("<merge /> must be the root element");
   } else {
    final View view = createViewFromTag(parent, name, context, attrs);
    final ViewGroup viewGroup = (ViewGroup) parent;
    final ViewGroup.LayoutParams params = viewGroup.generateLayoutParams(attrs);
    rInflateChildren(parser, view, attrs, true); // 继续遍历
    viewGroup.addView(view, params); // 顶层 View 添加 子 View
   }
  }
  if (finishInflate) { // 遍历解析
   parent.onFinishInflate();
  }
 }