在绘图程序中添加撤销功能。

I followed a raywenderlich tutorial on using the UIKit to make a drawing app. I'm now trying to add in the functionality to undo the last stroke. Ideally I would like to undo up to 10ish strokes. I'm trying to figure out what is the best way to go about doing this. I was thinking of creating another ImageView which has only the last stroke and making the on using th