A drawable wrapper that caches the drawing layer, used for caching gradients on older devices.

CachingDrawable.java

public class CachingDrawable extends Drawable {

    private final Drawable mDrawable;

    private final Config mConfig;

    private Bitmap mBitmap;

    public CachingDrawable(Drawable drawable) {
        this(drawable, Config.ARGB_8888);
    }

    public CachingDrawable(Drawable drawable, Config config) {
        mDrawable = drawable;
        mConfig = config;
    }

    @Override
    public void draw(Canvas canvas) {
        if (mBitmap == null) {
            Rect bounds = getBounds();
            int height = bounds.height();
            int width = bounds.width();
            if (height > 0 && width > 0) {
                mDrawable.setBounds(bounds);
                mBitmap = Bitmap.createBitmap(width, height, mConfig);
                mDrawable.draw(new Canvas(mBitmap));
                canvas.drawBitmap(mBitmap, 0, 0, null);
            } else {
                invalidateSelf();
            }
        } else {
            canvas.drawBitmap(mBitmap, 0, 0, null);
        }
    }

    @Override
    public int getOpacity() {
        return mConfig == Config.RGB_565 ? PixelFormat.OPAQUE : PixelFormat.TRANSLUCENT;
    }

    @Override
    public void setAlpha(int alpha) {
        mDrawable.setAlpha(alpha);
        mBitmap = null;
        invalidateSelf();
    }

    @Override
    public void setColorFilter(ColorFilter cf) {
        mDrawable.setColorFilter(cf);
        mBitmap = null;
        invalidateSelf();
    }
}