Runtime (ii): The black magic of the unconscious of the modified class method

If we want to rewrite the method of a class, what methods do we take into account?

1. Classification: The main disadvantage of classification is that the classification is not a parent class and cannot call a method of the parent class. and need to introduce the header file, easy to be found.

2. Inheritance: Although inheritance can implement the method of overriding the parent class, the action is too large to be discovered by others.

3.runtime: Method Exchange! Although the classification is used, but! No need to introduce header file!!

Nonsense not much to say directly on the code

1. Write a classification for Uicolor and introduce #import <objc/message.h>

#import <UIKit/UIKit.h>@interface  uicolor (extension)+ (uicolor*) My_redcolor; @end

#import "Uicolor+extension.h"#import<objc/message.h>@implementationuicolor (extension)//This method will be called when the classification is loaded.+ (void) load{Method Redmethod= Class_getclassmethod ([uicolorclass], @selector (Redcolor)); Method Myredmethod= Class_getclassmethod ([uicolorclass], @selector (My_redcolor)); Method_exchangeimplementations (Redmethod, Myredmethod);}+ (Uicolor *) my_redcolor{NSLog (@"111111"); //1. Modify the modification method directly    return[Uicolor Graycolor]; //2. Call the previous method, it should be noted that this time [Uicolor My_redcolor] actually executed is: Redcolor this method. This time if using [Uicolor Redcolor] will cause a dead loop. //return [Uicolor Redcolor];}@end

2. There is no need for any introduction, so long as the [Uicolor Redcolor] is called in any class, the method Exchange is implemented.

For example: Controller Self.view.backgroundColor = [Uicolor Redcolor];

Runtime (ii): The black magic of the unconscious of the modified class method