android 获取屏幕视图

public Bitmap getScreenShot() {
    View decorView = this.getWindow().getDecorView();
    View contentView = decorView.findViewById(android.R.id.content);
    contentView.setDrawingCacheEnabled(true);
    int num= 3;
    Bitmap cache = null;
    Bitmap bitmap = null;
    while (tryNumber > 0) {
        cache = contentView.getDrawingCache();
        if (cache != null) {
            bitmap = Bitmap.createBitmap(cache);
            break;
        }
        num--;
    }
    contentView.setDrawingCacheEnabled(false);

    return bitmap;
}