使用布局充气器将外部XML布局转换为位图

所以我有以下布局叫做demo_text.xml

我想将此demo_text转换为Bitmap.这是我的onCreate:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    View inflatedFrame = getLayoutInflater().inflate(R.layout.demo_text, null);
    FrameLayout frameLayout = (FrameLayout) inflatedFrame.findViewById(R.id.screen) ;
    frameLayout.setDrawingCacheEnabled(true);
    frameLayout.buildDrawingCache();
    Bitmap bm = frameLayout.getDrawingCache();

}

我希望位图是整个布局,但Bitmap总是返回null.

以下代码有效:

    View inflatedFrame = getLayoutInflater().inflate(R.layout.demo_text, null);
    FrameLayout frameLayout = (FrameLayout) inflatedFrame.findViewById(R.id.screen) ;
    frameLayout.setDrawingCacheEnabled(true);
    frameLayout.measure(View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED),
            View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED));
    frameLayout.layout(0, 0, frameLayout.getMeasuredWidth(), frameLayout.getMeasuredHeight());
    frameLayout.buildDrawingCache(true);
    final Bitmap bm = frameLayout.getDrawingCache();