[Android] setContentView源码分析

override fun onCreate(savedInstanceState: Bundle?) {
   super.onCreate(savedInstanceState)
   setContentView(R.layout.activity_main)
}

@Override
public void setContentView(@LayoutRes int layoutResID) {
  //返回了AppCompatDelegate对象
  getDelegate().setContentView(layoutResID);
}

@NonNull
public AppCompatDelegate getDelegate() {
  if (mDelegate == null) {
//跳转到create()方法可以看到,该方法返回的是一个AppCompatDelegateImpl对象
    mDelegate = AppCompatDelegate.create(this, this);
  }
  return mDelegate;
}

@Override
public void setContentView(View v) {
  ensureSubDecor();
  ViewGroup contentParent = (ViewGroup) mSubDecor.findViewById(android.R.id.content);
  contentParent.removeAllViews();
  LayoutInflater.from(mContext).inflate(resId, contentParent);
  mOriginalWindowCallback.onContentChanged();
}

private ViewGroup createSubDecor() {
  ....
  //步骤1
  //mWindow是PhoneWindow,该对象是在Activity.java attach()方法中初始化
  //该方法会触发DecorView的创建
  mWindow.getDecorView();
  ...
  //根据不同的情形加载不同的布局文件来初始化subDecor,具体过程可以不细究
  ...
  //步骤2
  //可以先看完之后的步骤可以再来看这里
  //调用PhoneWindow.setContentView()方法,将创建好的subDecor添加到mContentParent,
  //mContentParent是在installDecor方法中调用generateLayout()创建出来的
  //在之后的Android版本中,我们的布局其实是添加到了subDecor中,而subDecor又会添加到
  //PhoneWindow.mContentParent,mContentParent其实是DecorView的一个子View,初始化过程见installDecor方法
  mWindow.setContentView(subDecor);
}

private void installDecor() {
  mForceDecorInstall = false;
  if (mDecor == null) {
//该方法会直接new DecorView()
    mDecor = generateDecor(-1);
...
...
  }
  if (mContentParent == null) {
    //生成一个FrameLayout,用于添加AppCompatDelegateImpl.createSubDecor()
    //中创建的subDecor,该view是在setContentView中添加的,见步骤2
    mContentParent = generateLayout(mDecor);
    final DecorContentParent decorContentParent = (DecorContentParent) mDecor.findViewById(
          R.id.decor_content_parent);
    if (decorContentParent != null) {
        mDecorContentParent = decorContentParent;
...
...
  }

protected DecorView generateDecor(int featureId) {
  ...
  ...
  return new DecorView(context, featureId, this, getAttributes());
}

protected ViewGroup generateLayout(DecorView decor){
   ...
   ...
   ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
   ...
   ...
   return contentParanet;
}

@Override
public void setContentView(int resId) {
  ensureSubDecor();
  //这个对象就是PhoneWindow下面的generateLayout()创建出来的FrameLayout
  ViewGroup contentParent = (ViewGroup) mSubDecor.findViewById(android.R.id.content);
  contentParent.removeAllViews();
  //最后将我们传进来的布局文件实例化,然后添加进去
  LayoutInflater.from(mContext).inflate(resId, contentParent);
  //最后会回调onContentChanged()生命周期方法
  mOriginalWindowCallback.onContentChanged();
}