self.delegate respondsToSelector: ... 无法编译

问题描述

限时删除！！

我已经实现了一个带有可选方法的协议，并且在调用方法中我想在发送消息之前将 respondsToSelector: 发送到 self.delegate，但是不编译.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:

选择器respondsToSelector"的未知实例方法.

作为一种变通方法，我清理"了如下所示的委托，它编译...

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];
}

.

我检查了许多帖子，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.

另外，替代访问器不起作用...

Also, alternative accessors do not work...

[self delegate]
//or
_delegate

有没有人看到这个或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.要么假设您的 id 委托实际上是一个 NSObject，然后进行转换:

-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，让你的委托明确地成为一个 NSObject:

Or, better, make your delegate explicitly an NSObject:

@property (nonatomic, weak) NSObject* delegate;

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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