在onCreate方法中动态创建contentView

Activity的onCreate方法中通常利用布局文件来构建ContentView。另一种比较实用的方法是：在代码中动态创建ContentView。如下所示：

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    gestureScanner = new GestureDetector(this);
    gestureScanner.setOnDoubleTapListener(doubleTapListener);
    main = new LinearLayout(this);
    main.setBackgroundColor(Color.GRAY);
    main.setLayoutParams(new LinearLayout.LayoutParams(320, 480));
    main.setOrientation(LinearLayout.VERTICAL);
    viewA = new TextView(this);
    viewA.setBackgroundColor(Color.YELLOW);
    viewA.setTextColor(Color.BLACK);
    viewA.setTextSize(16);
    viewA.setLayoutParams(new LinearLayout.LayoutParams(320, 50));
    main.addView(viewA);
    setContentView(main);
}