为什么不删除图像，而不修改图像的该部分的alpha值.然后，当您需要它时，可以修改Alpha.

Instead of erasing, why don't you modify the alpha for that part of the image. Then when you want it back, you modify the alpha back.

否则，当底部的图像被删除时，您应该恢复整个上方的图像.

Otherwise you should restore the entire upper image when the bottom one is erased.