Android View.getDrawingCache返回null,仅返回null

Question

有人请尝试向我解释原因

public void addView(View child) {
  child.setDrawingCacheEnabled(true);
  child.setWillNotCacheDrawing(false);
  child.setWillNotDraw(false);
  child.buildDrawingCache();
  if(child.getDrawingCache() == null) { //TODO Make this work!
    Log.w("View", "View child's drawing cache is null");
  }
  setImageBitmap(child.getDrawingCache()); //TODO MAKE THIS WORK!!!
}

ALWAYS记录绘图缓存为空,并将位图设置为null？

在设置缓存之前,我是否必须实际绘制视图？

谢谢!

Answer 1

我也有这个问题,并找到了这个答案:

v.setDrawingCacheEnabled(true);

// this is the important code :)  
// Without it the view will have a dimension of 0,0 and the bitmap will be null          
v.measure(MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED), 
            MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED));
v.layout(0, 0, v.getMeasuredWidth(), v.getMeasuredHeight()); 

v.buildDrawingCache(true);
Bitmap b = Bitmap.createBitmap(v.getDrawingCache());
v.setDrawingCacheEnabled(false); // clear drawing cache

Answer 2

如果getDrawingCache总是returning null伙计:使用这个:

public static Bitmap loadBitmapFromView(View v) {
     Bitmap b = Bitmap.createBitmap( v.getLayoutParams().width, v.getLayoutParams().height, Bitmap.Config.ARGB_8888);                
     Canvas c = new Canvas(b);
     v.layout(0, 0, v.getLayoutParams().width, v.getLayoutParams().height);
     v.draw(c);
     return b;
}

参考:https://stackoverflow.com/a/6272951/371749

Answer 3

获得null的基本原因是视图不是维数.然后,使用view.getWidth(),view.getLayoutParams().width等进行所有尝试,包括view.getDrawingCache()和view.buildDrawingCache(),都是无用的.因此,您首先需要为视图设置尺寸,例如:

view.layout(0, 0, width, height);

(您已经根据需要设置了'width'和'height',或者使用WindowManager等获取它们)