为什么检查UIGestureRecognizer在iPhone OS 3.0上找到它，当它在3.2中引入时？

I'm using UIGestureRecognizer for the first time and I want my app to run on iOS 3.0 onwards. Since Apple clearly states that the library is available in iOS 3.2 and later I used the following code:I'm using UIGestureRecognizer for the first tim