objective-c / ios跟踪屏幕使用情况

Question

Let's say, for instance, that I want to place some code in the viewDidAppear: method for all UIViewController (including subclasses) objects from my project:

-(void)viewDidAppear:(BOOL)animated{
    [super viewDidAppear:animated];

    NSLog(@"Did show: %@:%@", NSStringFromClass([self class]), self.title);
}

Is there a way to do this without using categories (for UIViewController ), and without having to manually change the superclass of all my view controllers to a new class that defines this method?
The reason I don't want to use a category is because I might want to define methods and call their super implementation.

For instance, is it possible to automatically add an intermediary class between UIViewController and whatever other classes inherit from UIViewController at runtime (or using preprocessor macros)?

Answer 1

The common way to achieve this is called method swizzling. Mike Ash has an article of how to do this correctly.

The general idea is to exchange the original implementation of an Objective-C method. Usually you call through to the original implementation from the inserted function/method.

Here's a quote from Mike's article:

The Obligatory Warning

Overriding methods on classes you don't own is a dangerous business. Your override could cause problems by breaking the assumptions of the class in question. Avoid it if it's at all possible. If you must do it, code your override with extreme care.