public static int getAlpha(@NonNull Drawable drawable) {
        if (Build.VERSION.SDK_INT >= 19) {
            return drawable.getAlpha();
        } else {
            return 0;
        }
    }
Get the alpha value of the {@code drawable}.
0 means fully transparent, 255 means fully opaque.

@param drawable The Drawable against which to invoke the method.
android/android_framework/base/src/main/java/github/tornaco/android/thanos/core/compat/DrawableCompat.java