OC消息转发

1 重载 resolveInstanceMethod: 和 resolveClassMethod: 方法动态添加实例方法实现和类方法实现

+ (BOOL)resolveInstanceMethod:(SEL)sel {


    if (sel == @selector(setName:)) {
        
        class_addMethod([self class], sel, (IMP)setName, "v@:@");
        return YES;
    }else if (sel == @selector(name)){
        
        class_addMethod([self class], sel, (IMP)getName, "@@:");
        return YES;
    }
    
    return [super resolveInstanceMethod:sel];
}

2 消息转发机制执行前，Runtime 系统允许我们替换消息的接收者为其他对象。通过 - (id)forwardingTargetForSelector:(SEL)aSelector 方法。

- (id)forwardingTargetForSelector:(SEL)aSelector
{
    if(aSelector == @selector(mysteriousMethod:)){
        return alternateObject;
    }
    return [super forwardingTargetForSelector:aSelector];
}

3 完整消息转发阶段

- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector { 
  if(aSelector == @selector(testMethod)) 
  { 
    return [NSMethodSignature signatureWithObjCTypes:"v@:"]; 
  } 
  return nil; 
} 
  
  
-(void)forwardInvocation:(NSInvocation *)anInvocation 
{ 
  if (anInvocation.selector == @selector(testMethod)) 
  { 
    TestModelHelper1 *h1 = [[TestModelHelper1 alloc] init]; 
    TestModelHelper2 *h2 = [[TestModelHelper2 alloc] init]; 
    [anInvocation invokeWithTarget:h1]; 
    [anInvocation invokeWithTarget:h2]; 
  } 
} 

forwardingTargetForSelector仅支持一个对象的返回，也就是说消息只能被转发给一个对象

forwardInvocation可以将消息同时转发给任意多个对象