需要将Drawable对象转换成Bitmap对象的时候使用的, 静态方法:

public static Bitmap drawableToBitmap(Drawable drawable) {
        try {
            Bitmap bitmap = Bitmap
                    .createBitmap(
                            drawable.getIntrinsicWidth(),
                            drawable.getIntrinsicHeight(),
                            drawable.getOpacity() != PixelFormat.OPAQUE ? Bitmap.Config.ARGB_8888
                                    : Bitmap.Config.RGB_565);
            Canvas canvas = new Canvas(bitmap);
            // canvas.setBitmap(bitmap);
            drawable.setBounds(0, 0, drawable.getIntrinsicWidth(),
                    drawable.getIntrinsicHeight());
            drawable.draw(canvas);

            return bitmap;
        } catch (OutOfMemoryError e) {
            e.printStackTrace();
            return null;
        }
    }