Android中将布局文件/View添加至窗口过程分析 ---- 从setContentView()谈起

public abstract class Window {    
    //...  
    //指定Activity窗口的风格类型  
    public static final int FEATURE_NO_TITLE = 1;  
    public static final int FEATURE_INDETERMINATE_PROGRESS = 5;  
      
    //设置布局文件  
    public abstract void setContentView(int layoutResID);  
  
    public abstract void setContentView(View view);  
  
    //请求指定Activity窗口的风格类型  
    public boolean requestFeature(int featureId) {  
        final int flag = 1<<featureId;  
        mFeatures |= flag;  
        mLocalFeatures |= mContainer != null ? (flag&~mContainer.mFeatures) : flag;  
        return (mFeatures&flag) != 0;  
    }      
    //...  
}  

public class PhoneWindow extends Window implements MenuBuilder.Callback {  
    //...  
    // This is the top-level view of the window, containing the window decor.  
    private DecorView mDecor;  //该对象是所有应用窗口的根视图 ， 是FrameLayout的子类  
      
    //该对象是Activity布局文件的父视图，一般来说是一个FrameLayout型的ViewGroup   
    // 同时也是DecorView对象的一个子视图  
    // This is the view in which the window contents are placed. It is either  
    // mDecor itself, or a child of mDecor where the contents go.  
    private ViewGroup mContentParent;   
      
    //设置标题  
    @Override  
    public void setTitle(CharSequence title) {  
        if (mTitleView != null) {  
            mTitleView.setText(title);  
        }  
        mTitle = title;  
    }  
    //设置背景图片  
    @Override  
    public final void setBackgroundDrawable(Drawable drawable) {  
        if (drawable != mBackgroundDrawable || mBackgroundResource != 0) {  
            mBackgroundResource = 0;  
            mBackgroundDrawable = drawable;  
            if (mDecor != null) {  
                mDecor.setWindowBackground(drawable);  
            }  
        }  
    }  
    //...      
}  

private final class DecorView extends FrameLayout {  
    //...  
    //触摸事件处理  
    @Override  
    public boolean onTouchEvent(MotionEvent event) {  
        return onInterceptTouchEvent(event);  
    }  
    //...  
}   

public void setContentView(int layoutResID) {  
    getWindow().setContentView(layoutResID);  
}  
  
public Window getWindow() {  
    return mWindow;   //Window对象，本质上是一个PhoneWindow对象  
}  

private void installDecor() {  
    if (mDecor == null) {  
        //mDecor为空，则创建一个Decor对象  
        mDecor = generateDecor();  
        mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);  
        mDecor.setIsRootNamespace(true);  
    }  
    if (mContentParent == null) {  
        //generateLayout()方法会根据窗口的风格修饰，选择对应的修饰布局文件  
        //并且将id为content(android:id="@+id/content")的FrameLayout赋值给mContentParent  
        mContentParent = generateLayout(mDecor);  
          
        //...  
}  

protected ViewGroup generateLayout(DecorView decor) {  
    // Apply data from current theme.  
  
    //...1、根据requestFreature()和Activity节点的android:theme="" 设置好 features值  
      
    //2 根据设定好的 features值，即特定风格属性，选择不同的窗口修饰布局文件  
    int layoutResource;  //窗口修饰布局文件    
    int features = getLocalFeatures();  
    // System.out.println("Features: 0x" + Integer.toHexString(features));  
    if ((features & ((1 << FEATURE_LEFT_ICON) | (1 << FEATURE_RIGHT_ICON))) != 0) {  
        if (mIsFloating) {  
            layoutResource = com.android.internal.R.layout.dialog_title_icons;  
        } else {  
            layoutResource = com.android.internal.R.layout.screen_title_icons;  
        }  
        // System.out.println("Title Icons!");  
    } else if ((features & ((1 << FEATURE_PROGRESS) | (1 << FEATURE_INDETERMINATE_PROGRESS))) != 0) {  
        // Special case for a window with only a progress bar (and title).  
        // XXX Need to have a no-title version of embedded windows.  
        layoutResource = com.android.internal.R.layout.screen_progress;  
        // System.out.println("Progress!");  
    }   
    //...  
      
    //3 选定了窗口修饰布局文件 ，添加至DecorView对象里，并且指定mcontentParent值  
    View in = mLayoutInflater.inflate(layoutResource, null);  
    decor.addView(in, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));  
  
    ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);  
    if (contentParent == null) {  
        throw new RuntimeException("Window couldn‘t find content container view");  
    }  
  
    if ((features & (1 << FEATURE_INDETERMINATE_PROGRESS)) != 0) {  
        ProgressBar progress = getCircularProgressBar(false);  
        if (progress != null) {  
            progress.setIndeterminate(true);  
        }  
    }  
    //...  
    return contentParent;  
}  

<!--  
This is an optimized layout for a screen, with the minimum set of features  
enabled.  
-->  
  
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"  
    android:orientation="vertical"  
    android:fitsSystemWindows="true">  
    <FrameLayout  
        android:layout_width="match_parent"   
        android:layout_height="?android:attr/windowTitleSize"  
        style="?android:attr/windowTitleBackgroundStyle">  
        <TextView android:id="@android:id/title"   
            style="?android:attr/windowTitleStyle"  
            android:background="@null"  
            android:fadingEdge="horizontal"  
            android:gravity="center_vertical"  
            android:layout_width="match_parent"  
            android:layout_height="match_parent" />  
    </FrameLayout>  
    <FrameLayout android:id="@android:id/content"  
        android:layout_width="match_parent"   
        android:layout_height="0dip"  
        android:layout_weight="1"  
        android:foregroundGravity="fill_horizontal|top"  
        android:foreground="?android:attr/windowContentOverlay" />  
</LinearLayout>  

@Override  
public void setContentView(int layoutResID) {  
    if (mContentParent == null) {  
        installDecor();  
    } else {  
        mContentParent.removeAllViews();  
    }  
    mLayoutInflater.inflate(layoutResID, mContentParent);  
    final Callback cb = getCallback();  
    if (cb != null) {  
        cb.onContentChanged();  
    }  
}  

//系统resume一个Activity时，调用此方法  
final void handleResumeActivity(IBinder token, boolean clearHide, boolean isForward) {  
    ActivityRecord r = performResumeActivity(token, clearHide);  
    //...  
     if (r.activity.mVisibleFromClient) {  
         r.activity.makeVisible();  
     }  
}