Android -- Drawable && Bitmap

Bitmap bm=xxx; 
BitmapDrawable bd=new BitmapDrawable(bm);

Drawable d=xxx; 
BitmapDrawable bd = (BitmapDrawable) d;
Bitmap bm = bd.getBitmap();

public static Bitmap getBitmapFromResources(Activity act, int resId) {
    Resources res = act.getResources();
    return BitmapFactory.decodeResource(res, resId);
}

public static Bitmap convertBytes2Bimap(byte[] b) {
    if (b.length == 0) {
        return null;
    }
    return BitmapFactory.decodeByteArray(b, 0, b.length);
}

public static byte[] convertBitmap2Bytes(Bitmap bm) {
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    bm.compress(Bitmap.CompressFormat.PNG, 100, baos);
    return baos.toByteArray();
}

public static Bitmap convertDrawable2BitmapByCanvas(Drawable drawable) {
    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;
}