Android View 源码解析(二) - LayoutInflater

  View in = mLayoutInflater.inflate(layoutResource, null);

  /**
   * Obtains the LayoutInflater from the given context.
   */
  public static LayoutInflater from(Context context) {
      LayoutInflater LayoutInflater =
              (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
      if (LayoutInflater == null) {
          throw new AssertionError("LayoutInflater not found.");
      }
      return LayoutInflater;
  }

  public View inflate(@LayoutRes int resource, @Nullable ViewGroup root) {
      return inflate(resource, root, root != null);
  }

  public View inflate(XmlPullParser parser, @Nullable ViewGroup root) {
    return inflate(parser, root, root != null);
  }

  public View inflate(@LayoutRes int resource, @Nullable ViewGroup root, boolean attachToRoot) {
      final Resources res = getContext().getResources();
      if (DEBUG) {
          Log.d(TAG, "INFLATING from resource: \"" + res.getResourceName(resource) + "\" ("
                  + Integer.toHexString(resource) + ")");
      }

      final XmlResourceParser parser = res.getLayout(resource);
      try {
          return inflate(parser, root, attachToRoot);
      } finally {
          parser.close();
      }
  }

public View inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot) {
        synchronized (mConstructorArgs) {
            Trace.traceBegin(Trace.TRACE_TAG_VIEW, "inflate");

            final Context inflaterContext = mContext;
            final AttributeSet attrs = Xml.asAttributeSet(parser);
            Context lastContext = (Context) mConstructorArgs[0];
            mConstructorArgs[0] = inflaterContext;
            //定义返回值 初始化传入形参 root
            View result = root;

            try {
                // 找到根节点
                int type;
                while ((type = parser.next()) != XmlPullParser.START_TAG &&
                        type != XmlPullParser.END_DOCUMENT) {
                }

                //验证type是否为Start_Tag  保证xml文件正确
                if (type != XmlPullParser.START_TAG) {
                    throw new InflateException(parser.getPositionDescription()
                            + ": No start tag found!");
                }

                //type为 root node
                final String name = parser.getName();

                if (DEBUG) {
                    System.out.println("**************************");
                    System.out.println("Creating root view: "
                            + name);
                    System.out.println("**************************");
                }

                if (TAG_MERGE.equals(name)) {
                    //处理 merge相关
                    //root需要非空 且attachToRoot为空
                    if (root == null || !attachToRoot) {
                        throw new InflateException("<merge /> can be used only with a valid "
                                + "ViewGroup root and attachToRoot=true");
                    }
                    //递归inflate 方法调用
                    rInflate(parser, root, inflaterContext, attrs, false);
                } else {
                    //根据tag节点创建view对象
                    final View temp = createViewFromTag(root, name, inflaterContext, attrs);

                    ViewGroup.LayoutParams params = null;

                    if (root != null) {
                        if (DEBUG) {
                            System.out.println("Creating params from root: " +
                                    root);
                        }
                        //根据root生成LayoutParams
                        params = root.generateLayoutParams(attrs);
                        if (!attachToRoot) {
                            //如果attachToRoot为flase 则调用setLayoutParams
                            temp.setLayoutParams(params);
                        }
                    }

                    if (DEBUG) {
                        System.out.println("-----> start inflating children");
                    }
                    //递归inflate剩下的children
                    rInflateChildren(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) {
                        //root非空且attachToRoot=true则将xml文件的root view加到形参提供的root里
                        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) {
                        //返回xml里解析的root view
                        result = temp;
                    }
                }

            } catch (XmlPullParserException e) {
                InflateException ex = new InflateException(e.getMessage());
                ex.initCause(e);
                throw ex;
            } catch (Exception e) {
                InflateException ex = new InflateException(
                        parser.getPositionDescription()
                                + ": " + e.getMessage());
                ex.initCause(e);
                throw ex;
            } finally {
                // Don't retain static reference on context.
                mConstructorArgs[0] = lastContext;
                mConstructorArgs[1] = null;
            }

            Trace.traceEnd(Trace.TRACE_TAG_VIEW);
            //返回参数root或xml文件里的root view
            return result;
        }
    }

   void rInflate(XmlPullParser parser, View parent, Context context,
           AttributeSet attrs, boolean finishInflate) throws XmlPullParserException, IOException {

       final int depth = parser.getDepth();
       int type;
       //XmlPullParser解析器的标准解析模式
       while (((type = parser.next()) != XmlPullParser.END_TAG ||
               parser.getDepth() > depth) && type != XmlPullParser.END_DOCUMENT) {
           //找到start_tag节点
           if (type != XmlPullParser.START_TAG) {
               continue;
           }
           //获取Name标记
           final String name = parser.getName();

           //private static final String TAG_REQUEST_FOCUS = "requestFocus";
           //处理requestFocus
           if (TAG_REQUEST_FOCUS.equals(name)) {
               parseRequestFocus(parser, parent);
           // private static final String TAG_TAG = "tag";
           //处理tag
           } else if (TAG_TAG.equals(name)) {
               parseViewTag(parser, parent, attrs);
           //private static final String TAG_INCLUDE = "include";
           //处理include
           } else if (TAG_INCLUDE.equals(name)) {
               //如果是根节点则抛出异常
               if (parser.getDepth() == 0) {
                   throw new InflateException("<include /> cannot be the root element");
               }
               parseInclude(parser, context, parent, attrs);
           //private static final String TAG_MERGE = "merge";
           //处理merge merge需要是xml中的根节点
           } 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);
               viewGroup.addView(view, params);
           }
       }

        //parent的所有子节点都处理完毕的时候回onFinishInflate方法
       if (finishInflate) {
           parent.onFinishInflate();
       }
   }
   //可以添加自定义逻辑
    protected void onFinishInflate() {
    }