Android11 调用系统分屏

在 Android 11 中，可以使用以下代码调用系统分屏：

if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.R) {
    final Rational rational = new Rational(3, 4); // 宽高比
    final int width = (int) (getWindowManager().getDefaultDisplay().getWidth() * rational.floatValue());
    final int height = getWindowManager().getDefaultDisplay().getHeight();
    final PictureInPictureParams.Builder pipBuilder = new PictureInPictureParams.Builder();
    pipBuilder.setAspectRatio(rational).setSourceRectHint(new Rect(0, 0, width, height));
    enterPictureInPictureMode(pipBuilder.build());
} else {
    // 在 Android 11 以下版本，使用旧的分屏模式
    final int flags = WindowManager.LayoutParams.FLAG_SPLIT_TOUCH | WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON;
    getWindow().setFlags(flags, flags);
    final WindowManager wm = (WindowManager) getSystemService(Context.WINDOW_SERVICE);
    final Display display = wm.getDefaultDisplay();
    final Point size = new Point();
    display.getSize(size);
    final int width = size.x / 2;
    final int height = size.y;
    final int x = size.x / 2;
    final int y = 0;
    final WindowManager.LayoutParams params = new WindowManager.LayoutParams(width, height, WindowManager.LayoutParams.TYPE_APPLICATION, flags, PixelFormat.RGBA_8888);
    params.gravity = Gravity.START | Gravity.TOP;
    params.x = x;
    params.y = y;
    wm.addView(getLayoutInflater().inflate(R.layout.activity_split_screen, null), params);
}

需要注意的是，在 Android 11 以下版本的分屏模式中，需要在布局文件中添加 `android:fitsSystemWindows="true"` 属性，以保证分屏后布局正确。