Android基于Window.ID_ANDROID_CONTENT给定id添加子View

这一技术特点在一些视频播放器中比较有用。

例如代码：

package zhangphil.demo;

import android.app.Activity;

import android.content.Context;

import android.content.ContextWrapper;

import android.support.v7.app.AppCompatActivity;

import android.os.Bundle;

import android.view.Gravity;

import android.view.View;

import android.view.ViewGroup;

import android.view.Window;

import android.widget.FrameLayout;

public class MainActivity extends AppCompatActivity {

private static final int VIEW_ID = 0xf0a01;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

//setContentView(R.layout.activity_main);

int w = 500;

int h = 500;

int gap = 100;

addView(w, h, getResources().getColor(android.R.color.holo_orange_light));

addView(w - gap, h - gap, getResources().getColor(android.R.color.holo_green_light));

addView(w - gap * 2, h - gap * 2, getResources().getColor(android.R.color.holo_red_light));

}

private void addView(int w, int h, int color) {

ViewGroup vp = (ViewGroup) (scanForActivity(this))//.getWindow().getDecorView();

.findViewById(Window.ID_ANDROID_CONTENT);

View old = vp.findViewById(VIEW_ID);

if (old != null) {

vp.removeView(old);

}

FrameLayout.LayoutParams params = new FrameLayout.LayoutParams(w, h, Gravity.CENTER);

FrameLayout newView = new FrameLayout(this);

newView.setBackgroundColor(color);

newView.setId(VIEW_ID);

vp.addView(newView, params);

}

public static Activity scanForActivity(Context context) {

if (context == null) return null;

if (context instanceof Activity) {

return (Activity) context;

} else if (context instanceof ContextWrapper) {

return scanForActivity(((ContextWrapper) context).getBaseContext());

}

return null;

}

}

运行结果：

如果在addView里面把这段代码注释掉：

// View old = vp.findViewById(VIEW_ID);

// if (old != null) {

// vp.removeView(old);

// }

运行结果。

这一特性如果巧妙加以利用可制作成特殊视频view的呈现。