ios – 协议的NSMethodSignature

我正在使用这种方法将方法分派给委托,不幸的是我发现大多数时候NSMethodSignature都是nil,这是因为选择器来自协议.我想知道哪种方法是正确的：

> Aks,如果方法来自协议
>获取协议方法的签名

[编辑]
根据newacct用户观察我的问题是不正确的,签名是零是正常的,但不是因为是协议,而是因为我要求方法签名对错误的对象.在这种情况下,它不实现我想要分派的方法,它是使用和实现它们的委托.

这是代码：

- (BOOL) dispatchToDelegate: (SEL) SELEctor withArg: (id) arg error: (NSError*) err {
 NSMethodSignature *methodSig = [[self class] instanceMethodSignatureForSELEctor:SELEctor];
 NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:methodSig]; 
[invocation setTarget:self.delegate]; 
BOOL result = NO; 
if([self.delegate respondsToSELEctor: SELEctor]) {
        if(arg != NULL) {
            [invocation setArgument:&arg aTindex:2];      
            [invocation setArgument:&err aTindex:3];  
    }else {
        [invocation setArgument:&err aTindex:2];      

    }
    if ([NSThread ismainThread]) {
        [invocation invoke];        
    }
    else{
        [invocation performSELEctorOnMainThread:@SELEctor(invokE) withObject:nil waitUntilDone:YES];
    }
    [invocation getReturnValue:&result];
}
else
    NSLog(@"Missed Method");
return result;
}

[更新答案]
我修改了Apple邮件列表中的方法

- (NSMethodSignature *)methodSignatureForSELEctor:(SEL)inSELEctor
{
    NSMethodSignature *theMethodSignature = [super methodSignatureForSELEctor:inSELEctor];
    if (theMethodSignature == NULL)
    {
        struct objc_method_description theDescription = protocol_getmethodDescription(@protocol(GameCenteRMANagerDelegatE),inSELEctor,NO,YES);
        theMethodSignature = [NSMethodSignature signatureWithObjCTypes:theDescription.types];
    }
    return(theMethodSignaturE);
}

它有效,但我会遵循bbum的建议,代码变得非常复杂……就像很快就会破解.

if ([delegate respondsToSELEctor:@SELEctor(someMethod:thatDoesSomething:)]) {
    dispatch_async(dispatch_get_main_queue(),^{
        [delegate someMethod:foo thatDoesSomething:bar];
    }
}