运行时

- (void)noReturnNoParams {
    NSLog(@"noReturnNoParams");
}

- (NSString *)hasReturnHasParams:(NSString *)params {
    NSLog(@"hasReturnHasParams:%@",params);
    
    return params;
}

调用

// 一般调用
[self noReturnNoParams];
[self hasReturnHasParams:@"params"];

// 通过objc_msgSend调用
((void(*)(id,SEL))objc_msgSend)(self,@selector(noReturnNoParams));
((NSString *(*)(id,SEL,NSString *))objc_msgSend)(self,@selector(hasReturnHasParams:),@"this is param");

// 通过函数地址调用
void (*setter)(id,SEL);
setter = (void(*)(id, SEL, BOOL))[self methodForSelector:@selector(noReturnNoParams)];
setter(self, @selector(noReturnNoParams));

消息转发

通过 obj_msgSend 调用，在找不到imp的时候，就会进入消息转发流程

1. 调用 + (BOOL)resolveInstanceMethod:(SEL)sel; 如果重写这个方法，动态添加未实现的方法，转发流程结束。

   + (BOOL)resolveInstanceMethod:(SEL)sel {
       NSLog(@"resolveInstanceMethod");
       
       if (sel == @selector(nofunction)) {
           
           IMP imp = imp_implementationWithBlock(^{
               NSLog(@"既然没有实现，那就动态添加方法");
           });
   
           class_addMethod([ObjcMsgSendVC class], sel, imp, "v@:");
           
             // return YES/NO不知道有什么作用，看起来没什么影响
           return NO;
       }
       
       return [super resolveInstanceMethod:sel];
   }
   
   

2. 触发 - (id)forwardingTargetForSelector:(SEL)aSelector ；可以指定一个对象来相应这个方法，如果返回nil,则进入下一步

   - (id)forwardingTargetForSelector:(SEL)aSelector {
       NSLog(@"forwardingTargetForSelector:");
       
       if (aSelector == @selector(nofunction)) {
           // Obviously if you return self from this method, the code would just fall into an infinite loop.
           // 但是系统做了优化，返回self也没事，但是不建议这么做
           return self.delegate;
       } else {
           return [super forwardingTargetForSelector:aSelector];
       }
   }
   

3. 正常转发，可以传递给多个对象

   - (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector {
       NSLog(@"methodSignatureForSelector:");
       
       if (aSelector == @selector(nofunction)) {
           // return nil;就不会调用下一步forwardInvocation:
           return [self methodSignatureForSelector:@selector(showWithAnimated:)];
       } else {
           return [super methodSignatureForSelector:aSelector];
       }
   }
   
   - (void)forwardInvocation:(NSInvocation *)anInvocation {
       NSLog(@"forwardInvocation:");
       
       if (anInvocation.selector == @selector(nofunction)) {
           NSLog(@"anInvocation.selector == @selector(nofunction)");
           
           [self showWithAnimated:YES];
           
       } else {
           [super forwardInvocation:anInvocation];
       }
   }
   

添加方法

SEL selector = @selector(test);
    
IMP imp =imp_implementationWithBlock(^{
    NSLog(@"这是方法实现");
});
    
Method method = class_getInstanceMethod([AddMethodVC class], selector);
    
class_addMethod([AddMethodVC class], selector, imp, method_getTypeEncoding(method));

方法交换

- (void)origin {
    NSLog(@"originMethod");
}

- (void)swizzle {
    NSLog(@"这是Swizzle方法实现");
}

- (void)swizzleMethod {
    SEL originSel = @selector(origin);
    SEL swizzleSel = @selector(swizzle);
    
    Method originMethod = class_getInstanceMethod([SwizzleMethodVC class], originSel);
    Method swizzleMethod = class_getInstanceMethod([SwizzleMethodVC class], swizzleSel);
    
    // 确定方法存在就可以直接交换，否则可以考虑，如果方法不存在，可以先添加
    BOOL didAddMethod = class_addMethod([SwizzleMethodVC class], originSel, method_getImplementation(swizzleMethod), method_getTypeEncoding(swizzleMethod));
    
    if (didAddMethod) {
        class_replaceMethod([SwizzleMethodVC class], swizzleSel, method_getImplementation(originMethod), method_getTypeEncoding(originMethod));
    } else {
        method_exchangeImplementations(originMethod, swizzleMethod);
    }
}

方法替换

- (void)replaceMethod {
    
//    Method method = class_getInstanceMethod([ReplaceMethodVC class], @selector(swizzle));
//
//    class_replaceMethod([ReplaceMethodVC class], @selector(origin), method_getImplementation(method), method_getTypeEncoding(method));
    
    Method method = class_getInstanceMethod([ReplaceMethodVC class], @selector(origin));
    
    IMP imp = imp_implementationWithBlock(^{
        NSLog(@"这是新的方法实现");
    });
    
    class_replaceMethod([ReplaceMethodVC class], @selector(origin), imp, method_getTypeEncoding(method));
}

- (void)origin {
    NSLog(@"originMethod");
}

- (void)swizzle {
    NSLog(@"这是Swizzle方法实现");
}

传送门

项目地址