在Objective C中,什么相当于在C中传递函数指针？

Question

@implementation ThisObject

-(void)start {

       SomeOtherObject *someOtherObject = [SomeOtherObject alloc];

       [someOtherObject doSomethingAndCallThisFunctionWhenUrDone:myCallBackFunction :self];

}

-(void)myCallBackFunction {

       // :)

}

基本上,我怎样才能做到这一点？

Answer 1

有四种方法可以进行回调:

1. 函数指针你可以做一个函数指针,如果你真的想要的,但并不推荐.它的完成方式与在C中执行的方式相同.问题是您不能使用指向Objective-C方法的函数指针.它看起来像这样:

   void callback(/* Some args */) {
       // Some callback.
   }
   
   - (void)doSomethingAndCallThisFunctionWhenDone:(void(*)(/* Some args */))func {
   
       // Do something.
   
       if (func)
           func(/* Some args */);
   }
   
   - (void)start {
       [self doSomethingAndCallThisFunctionWhenDone:&callback];
   }
   

2. 选择器您可以使用-performSelector:.它看起来像这样:

   - (void)doSomethingAndCallTarget:(id)target withSelector:(SEL)sel {
   
       // Do something.
   
       [target performSelector:sel];
   }
   
   - (void)start {
   
       SomeOtherObject * someOtherObject = [[SomeOtherObject alloc] init];
   
       [self doSomethingAndCallTarget:someOtherObject withSelector:@selector(MyCallback)];
   }
   

3. 代表使用代表.这类似于UITableViewDelegate/UITableViewDataSource.请在此处查看Apple文档.你可以这样做:

   - (void)doSomethingDelegate:(id<MyCallbackObject>)delegate {
   
       [delegate retain];
   
       // Do something.
   
       [delegate performMyCallback];  // -performMyCallback must be declared in the MyCallbackObject protocol and implemented by SomeOtherObject.
   
       [delegate release];
   }
   
   - (void)start {
   
       id<MyCallbackObject> someOtherObject = [[SomeOtherObject alloc] init];
   
       [self doSomethingDelegate:someOtherObject];
   
       [someOtherObject release];
   }
   

4. 块回调的首选方法是使用块.它们仅适用于iOS 4.0+或Mac OS X 10.6+.它看起来像这样:

   - (void)doSomethingAndCallThisBlockWhenDone:(void(^)(/* Some args */))block {
   
       [block copy];
   
       // Do something.
   
       if (block)
           block(/* Some args */);
   
       [block release];
   }
   
   - (void)start {
       [self doSomethingAndCallThisBlockWhenDone:^void(/* Some args */){   // Return type and arguments may be omitted if you don't have any.
           // Your callback
       }];
   }
   

正如您在块中看到的那样,它更容易阅读,并且您的回调与您的代码内联.这特别好,所以你不必追捕它.块有许多好处,但我不可能在这里全部覆盖它们.

最后一件事,如果你使用一个块,你会想要使用一个,typedef所以你不必像往常一样输入模糊的块类型void(^)(/* Some args */).本typedef看起来是这样的:

typdef void(^MyCallback)(/* Some args */);

然后,您可以像这样声明您的方法:

- (void)doSomethingAndCallThisBlockWhenDone:(MyCallback)block;

更新:

我已经展示了如何实现不同技术的更多细节(见上文).

Answer 2

你在说这个吗？

-(void)callSomePassedSelector:(SEL)callbackSelector {
    [someObjectThatRespondesToThisSelector performSelector:callbackSelector];
}

我假设您想存储它并稍后调用它，但这应该为您提供有关如何传递和调用它的所有所需信息。还有其他方法可以调用选择器，请参阅此处