Android - 自定义ImageView，勾选标记为选中的图像

For an Android app I'm building, I made a custom ImageView class which needs to show a tick over the image indicating this image has been selected. I loaded the tick image from a drawable resource and displayed it on top of the image, and it works fine. But what I want to do is that, when the tick is visible (that is, when the image is selected), the image to become darker so that you can see the tick clearly. How can I do this?For an Android app I'm building, I made a custo