相关疑难解决方法(0)

self.delegate respondsToSelector:...不编译

我已经实现了一个协议,一个可选的方法和调用方法我想发respondsToSelector:到self.delegate之前,我发送消息,但是,这并不编译.失败消息是:

没有已知的选择器'respondsToSelector'的实例方法.

作为解决方案,我"清理"了如下所示的代表,它编译了...

//MyClass.h:

@class MyClass;

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

@interface MyClass : UIViewController

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

@end

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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];
}

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我检查了一些帖子,包括这个,但它没有回答编译失败问题.

此外,替代访问器不起作用......