iOS 和 UIKit 类检查

Question

如何以编程方式检查 UIKit 是否有给定的类？

例如，在 iOS3 上没有 UINib，但在 iOS4 上有。我可以在 SDK4 上构建，但如果我尝试在 iOS3.0 设备上运行，我会遇到异常。

Answer 1

iOS 4 release notes状态:

iOS 4 includes a new UINib class to support rapidly unarchiving nib files. While this class is new to iOS SDK 4, it was present but private, in previous releases. Special care needs to be taken when deploying code that uses the UINib class and also runs on iOS releases prior to version 4. Specifically, you cannot determine the availability of the class solely using the NSClassFromString function, because that check returns a private class on iOS 3.x and earlier. Instead, after getting the UINib class using NSClassFromString, you must also use the respondsToSelector: method of the returned class to see if it responds to the nibWithNibName:bundle: method. If it responds to that method, you can use the class.