self.delegate respondsToSelector：...不编译 [英] self.delegate respondsToSelector: ... does not compile

问题描述

我已经使用可选方法实现了一个协议，在调用方法中我想将 respondsToSelector：发送到 self.delegate 在我发送消息之前，但是没有编译。失败消息是：

I've implemented a protocol with an optional method and in the calling method I want to send respondsToSelector: to self.delegate before I send the message, but that does not compile. The fail message is:

否选择器'respondsToSelector'的已知实例方法。

作为解决方法，我清理了如下所示的代理，它编译了......

As a work-around, I "sanitized" the delegate as shown below, which compiles...

//MyClass.h:

@class MyClass;

@Protocol MyClassDelegate
- (void)myClass:(MyClass *)sender willDoSomething:(BOOL)animated;
@end

@interface MyClass : UIViewController

@property (nonatomic, weak) id<MyClassDelegate> delegate;

@end

和

//MyClass.m:

...
@synthesize delegate = _delegate;
...

id sanitizedDelegate = self.delegate; //Hmmmm... why does this work?

if ([sanitizedDelegate respondsToSelector:@selector(myClass:willDoSomething:)]) {
    [self.delegate myClass:self willDoSomething:animated];
}

。

我检查了一些帖子，包括这个，但它没有回答编译失败问题。

I checked a number of posts including this one but it does not answer the compilation fail issue.

此外，替代访问者不起作用...

Also, alternative accessors do not work...

[self delegate]
//or
_delegate

有没有人看过这个或者可以建议更好的处理方式？

Has anyone seen this or can advise a better way of handling?

IOS 5.0：（9A334），Xcode 4.2.1（4D502）

IOS 5.0:(9A334), Xcode 4.2.1 (4D502)

推荐答案

-respondsToSelector：是NSObject上的一个方法。假设您的 id 委托实际上是一个NSObject，并将其强制转换：

-respondsToSelector: is a method on NSObject. Either assume that your id delegate is in fact an NSObject, and cast it:

[（NSObject *）self.delegate respondsToSelector：@ selector（myClass：willDoSomething :)）

或者，更好的是，明确地让你的委托NSObject：

Or, better, make your delegate explicitly an NSObject:

@property（非原子，弱）NSObject< MyClassDelegate> *委托;

或者使协议成为NSObject的子协议：

Or make the protocol be a sub-protocol of NSObject:

@protocol MyClassDelegate< NSObject>

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