Runtime method substitution and dynamic Add instance method combined with

The method substitution, can replace any external class's method, but the dynamic addition method can only implement in the object which the added class creates, but uses the method substitution and the dynamic addition method to use, may implement, the arbitrary external class dynamically adds the necessary method, this method may be the class method also may be the instance method, This external class can also be a class that does not have any method declarations and implementations.

Main idea: Using the run-time method to replace will be in the external class will be the custom method hy_resolveInstanceMethod or hy_resolveClassMethod (with the hy_ prefix is my custom method) and need to be added in the class resolveInstanceMethod or resolveClassMethod method substitution, replace before hy_resolveInstanceMethod or hy_resolveClassMethod inside the method is written in the resolveInstanceMethodor the resolveClassMethod logic of how the runtime dynamically adds the method is written internally.

A bit around, but at least need to continue to read the source code, thinking about the logic, in fact, is not difficult, the premise is familiar with the use of the runtime method.

Defects: 1, the method with parameters is difficult to handle, parameter values need to be based on the actual business logic.

Before use import <objc/message.h>, need following:

Create Person.h and PERSON.M

Person.h:

1 #import <Foundation/Foundation.h>23@interface  person:nsobject 4 5 @end

person.m:

1 #import " Person.h " 2 3 @implementation  Person 4 5 @end

Create OtherPerson.h and OTHERPERSON.M

OtherPerson.h:

1 #import <Foundation/Foundation.h>23@interface  otherperson:nsobject  456@end

OTHERPERSON.M:

1 //2 //Created by Heyang on 16/1/11.3 //copyright©2016 year Heyang. All rights reserved.4 //5 6 #import "OtherPerson.h"7 #import<objc/message.h>8 9 @implementationOtherpersonTen  One  A+(void) load{ -Class clazz = nsclassfromstring (@" Person"); -      the     //gets the class method before the substitution -Method instance_eat = - Class_getclassmethod (Clazz, @selector (resolveinstancemethod:)); -     //get the Substituted class method +Method instance_noteat = - Class_getclassmethod (Self, @selector (hy_resolveinstancemethod:)); +      A     //then the Exchange class method at method_exchangeimplementations (Instance_eat, instance_noteat); -      -     //gets the class method before the substitution -Method class_eat = - Class_getclassmethod (Clazz, @selector (resolveclassmethod:)); -     //get the Substituted class method inMethod class_noteat = - Class_getclassmethod (Self, @selector (hy2_resolveclassmethod:)); to      +     //then the Exchange class method - method_exchangeimplementations (Class_eat, class_noteat); the      * } $ Panax Notoginseng voidEat_1 (IDSelf,sel SEL) - { theNSLog (@"We 're not eating anymore."); +NSLog (@"%@ %@", Self,nsstringfromselector (SEL)); A } the voidEat_2 (IDSelf,sel SEL, nsstring* str1,nsstring*str2) + { -NSLog (@"We 're not eating anymore."); $NSLog (@"%@ %@", Self,nsstringfromselector (SEL)); $NSLog (@"print two parameter values:%@ and%@", STR1,STR2); - } -  the  -+(BOOL) Hy_resolveinstancemethod: (SEL) sel{Wuyi     //when SEL is a eat method in the implementation method the     if(sel = = nsselectorfromstring (@"Eat")) { -         //adding eat methods on the fly Wu          -         //first argument: which class to add a method to About         //Second parameter: Method number for adding a method $         //Third parameter: Add a function implementation of a method (function address) -         //The fourth parameter: the type of the function, (return value + parameter type) v:void @: Object->self: Represents Sel->_cmd -Class_addmethod (Self, SEL, (IMP) eat_1,"[email protected]:"); -     } A     returnYES; + } the+(BOOL) Hy2_resolveclassmethod: (SEL) sel{ -      $     if(sel = = nsselectorfromstring (@"Eat:with:")) { the          theClass_addmethod (Objc_getmetaclass (" Person"), SEL, (IMP) eat_2,"v#:@@"); the     } the      -     returnYES; in } the  the @end

Last in file ' main.m ':

MAIN.M:

1 /**2  *3 * Swap method and dynamic Add method (Exchange methods and dynamically add methods)4  *5  */6  7 #import<Foundation/Foundation.h>8 9 //ignore undeclared warm ignores undeclared warningsTen #pragmaClang Diagnostic push One #pragmaClang diagnostic ignored "-wundeclared-selector" A  - intMainintargcConst Char*argv[]) { - @autoreleasepool { the         //get this person class gets the person category -Class clazz = nsclassfromstring (@" Person"); -         //get this person Instance get the person instance -         IDperson =[[Clazz alloc] init]; +          -         //send message to ' eat ' method in person Class or person Instance +         //the ' eat ' method that sends a message to the person class or person instance does not contain parameters A [Person Performselector: @selector (Eat) withobject:nil]; at         //the ' eat ' method that sends a message to the person class contains two parameters - [Clazz performselector: @selector (eat:with:) -Withobject:@"Hello"  -Withobject:@" World"]; -     } -     return 0; in } -  to #pragmaClang Diagnostic Pop

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Runtime method substitution and dynamic Add instance method combined with