这是适用于iOS 8和Swift的解决方案。

Here's a working solution for iOS 8 and Swift.

func enableCancleButton (searchBar : UISearchBar) {
    for view1 in searchBar.subviews {
        for view2 in view1.subviews {
            if view2.isKindOfClass(UIButton) {
                var button = view2 as! UIButton
                button.enabled = true
                button.userInteractionEnabled = true
            }
        }
    }
}