/**
* Create drawable from a bitmap, setting initial target density based on
* the display metrics of the resources.
*/
public BitmapDrawable(Resources res, Bitmap bitmap) {
this(new BitmapState(bitmap), res);
mBitmapState.mTargetDensity = mTargetDensity;
}
原文：http://www.cnblogs.com/jianglijs/p/7454570.html