关于Object-C中的类别：覆盖现有消息
类别是子类化的替代方案。如果类别消息已在类中实现，将会发生什么情况。以UIViewController为例，
@implementation UIViewController (Landscape)
// Override to allow orientations other than the default portrait orientation.
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation {
// Return YES for supported orientations.
return (interfaceOrientation == UIInterfaceOrientationLandscapeRight || interfaceOrientation == UIInterfaceOrientationLandscapeLeft);
}
@end
那么如果我们得到任何扩展UIViewController的XXViewController，默认消息是否会像上面那样实现？
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
正如你所看到的，我的目标是让所有的XXViewController都支持landscape，所以使用category来达到这个目的。
实际上传统的策略会使用子类，并且它是有效的。类别方式怎么样？
谢谢
Category is alternative of subclassing. What will happen if the category message already has been implemented in the class. Take UIViewController as example,
@implementation UIViewController (Landscape)
// Override to allow orientations other than the default portrait orientation.
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation {
// Return YES for supported orientations.
return (interfaceOrientation == UIInterfaceOrientationLandscapeRight || interfaceOrientation == UIInterfaceOrientationLandscapeLeft);
}
@end
So if we get any XXViewController which extends UIViewController, is that the default message will be implemented like above ?
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
As you can see that I aim to make all XXViewController support landscape, so use category to reach this purpose.
Actually the traditional strategy will use subclass, and it works. How about the category way ?
Thanks
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类别确实可以覆盖方法；您的代码片段完全合法并且应该执行您想要的操作。
但是，您必须小心，就好像两个类别覆盖相同的方法一样，您将得到未定义的结果。另外，如果将来您希望某些视图控制器是纵向的，那么类别可能是一个糟糕的选择。
子类化可能是这里最好的选择。
Categories can indeed override methods; your code snippet is perfectly legal and should do what you want.
You do have to be careful, however, as if 2 categories override the same method you will get undefined results. Also, a category might be a bad choice if in the future you want some view controllers to be portrait.
Subclassing is probably the best option here.
您可能想要使用类集群方法或方法混合。
此处已经介绍了具有类似问题的主题：类别冲突
You may want to use Class Cluster approach, or methods swizzling.
A topic with similar question has been already covered here: Category conflicts