xcode self.delegate respondsToSelector: ... 不编译
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self.delegate respondsToSelector: ... does not compile
提问by vmanjz
I've implemented a protocol with an optional method and in the calling method I want to send respondsToSelector:to self.delegatebefore I send the message, but that does not compile. The fail message is:
我已经使用可选方法实现了一个协议，并且在我发送消息之前要发送respondsToSelector:到的调用方法中self.delegate，但它无法编译。失败消息是：
No Known instance method for selector 'respondsToSelector'.
选择器 'respondsToSelector' 没有已知的实例方法。
As a work-around, I "sanitized" the delegate as shown below, which compiles...
作为一种解决方法，我“清理”了如下所示的委托，它编译...
//MyClass.h:
@class MyClass;
@Protocol MyClassDelegate
- (void)myClass:(MyClass *)sender willDoSomething:(BOOL)animated;
@end
@interface MyClass : UIViewController
@property (nonatomic, weak) id<MyClassDelegate> delegate;
@end
and
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];
}
.
.
I checked a number of posts including this onebut it does not answer the compilation fail issue.
我检查了许多帖子，包括这个帖子，但它没有回答编译失败问题。
Also, alternative accessors do not work...
此外，替代访问器不起作用......
[self delegate]
//or
_delegate
Has anyone seen this or can advise a better way of handling?
有没有人看到这个或可以建议更好的处理方式？
IOS 5.0:(9A334), Xcode 4.2.1 (4D502)
IOS 5.0:(9A334), Xcode 4.2.1 (4D502)
回答by Kurt Revis
-respondsToSelector:is a method on NSObject. Either assume that your iddelegate is in fact an NSObject, and cast it:
-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，然后将其转换为：
[(NSObject*)self.delegate respondsToSelector:@selector(myClass:willDoSomething:)]
[(NSObject*)self.delegate respondsToSelector:@selector(myClass:willDoSomething:)]
Or, better, make your delegate explicitly an NSObject:
或者，更好的是，让您的委托明确成为 NSObject：
@property (nonatomic, weak) NSObject<MyClassDelegate>* delegate;
@property (nonatomic, weak) NSObject<MyClassDelegate>* delegate;
Or make the protocol be a sub-protocol of NSObject:
或者让协议成为 NSObject 的子协议：
@protocol MyClassDelegate <NSObject>
@protocol MyClassDelegate <NSObject>
回答by NJones
Basically you are saying that your delegate is constrained only by your <MyClassDelegate>protocol so the compiler assumes that those are the only methods available. What you need to do is have the protocol extend <NSObject>like so:
基本上，您是说您的委托仅受您的<MyClassDelegate>协议约束，因此编译器假定这些是唯一可用的方法。你需要做的是让协议<NSObject>像这样扩展：
@Protocol MyClassDelegate <NSObject>
- (void)myClass:(MyClass *)sender willDoSomething:(BOOL)animated;
@end
That way the compiler knows that any object which conforms to your protocol also conforms to the <NSObject>protocol which defines respondsToSelector:.
这样编译器就知道任何符合您的协议的对象也符合<NSObject>定义respondsToSelector:.
