@ property(副本)无效

@property (copy)void (^doStuff)(void);

实际的苹果文档，它精确地说明了使用什么:

苹果doco。

你的。h文件:

// Here is a block as a property:
//
// Someone passes you a block. You "hold on to it",
// while you do other stuff. Later, you use the block.
//
// The property 'doStuff' will hold the incoming block.

@property (copy)void (^doStuff)(void);

// Here's a method in your class.
// When someone CALLS this method, they PASS IN a block of code,
// which they want to be performed after the method is finished.

-(void)doSomethingAndThenDoThis:(void(^)(void))pleaseDoMeLater;

// We will hold on to that block of code in "doStuff".

你的。m文件:

 -(void)doSomethingAndThenDoThis:(void(^)(void))pleaseDoMeLater
    {
    // Regarding the incoming block of code, save it for later:
    self.doStuff = pleaseDoMeLater;
  
    // Now do other processing, which could follow various paths,
    // involve delays, and so on. Then after everything:
    [self _alldone];
    }

-(void)_alldone
    {
    NSLog(@"Processing finished, running the completion block.");
    // Here's how to run the block:
    if ( self.doStuff != nil )
       self.doStuff();
    }

注意过时的示例代码。

对于现代(2014+)系统，这是正确的和文档化的方法。

下面是一个如何完成这样一个任务的例子:

#import <Foundation/Foundation.h>
typedef int (^IntBlock)();

@interface myobj : NSObject
{
    IntBlock compare;
}

@property(readwrite, copy) IntBlock compare;

@end

@implementation myobj

@synthesize compare;

- (void)dealloc 
{
   // need to release the block since the property was declared copy. (for heap
   // allocated blocks this prevents a potential leak, for compiler-optimized 
   // stack blocks it is a no-op)
   // Note that for ARC, this is unnecessary, as with all properties, the memory management is handled for you.
   [compare release];
   [super dealloc];
}
@end

int main () {
    @autoreleasepool {
        myobj *ob = [[myobj alloc] init];
        ob.compare = ^
        {
            return rand();
        };
        NSLog(@"%i", ob.compare());
        // if not ARC
        [ob release];
    }

    return 0;
}

现在，如果你需要改变比较的类型，唯一需要改变的是typedef int (^IntBlock)()。如果你需要传递两个对象给它，将其更改为:typedef int (^IntBlock)(id, id)，并将你的块更改为:

^ (id obj1, id obj2)
{
    return rand();
};

2012年3月12日编辑:

对于ARC，不需要进行特定的更改，因为ARC将为您管理这些块，只要它们被定义为副本。你也不需要在析构函数中将属性设置为nil。

如需更多阅读，请查看以下文件: http://clang.llvm.org/docs/AutomaticReferenceCounting.html

当然，您可以使用块作为属性。但是要确保它们被声明为@property(copy)。例如:

typedef void(^TestBlock)(void);

@interface SecondViewController : UIViewController
@property (nonatomic, copy) TestBlock block;
@end

在MRC中，捕获上下文变量的块分配在堆栈中;当堆栈帧被销毁时，它们将被释放。如果复制了它们，将在堆中分配一个新的块，该块可以在堆栈帧弹出后执行。

@property (nonatomic, copy) void (^simpleBlock)(void);
@property (nonatomic, copy) BOOL (^blockWithParamter)(NSString *input);

如果你要在几个地方重复同一个块，请使用类型def

typedef void(^MyCompletionBlock)(BOOL success, NSError *error);
@property (nonatomic) MyCompletionBlock completion;

Disclamer

这并不是“好的答案”，因为这个问题明确地要求objective - c。苹果在WWDC14上介绍了Swift，我想分享一下在Swift中使用block(或闭包)的不同方式。

你好,迅速

在Swift中，你有很多方法来传递一个相当于函数的块。

我找到了三个。

为了理解这一点，我建议你在操场上测试这一小段代码。

func test(function:String -> String) -> String
{
    return function("test")
}

func funcStyle(s:String) -> String
{
    return "FUNC__" + s + "__FUNC"
}
let resultFunc = test(funcStyle)

let blockStyle:(String) -> String = {s in return "BLOCK__" + s + "__BLOCK"}
let resultBlock = test(blockStyle)

let resultAnon = test({(s:String) -> String in return "ANON_" + s + "__ANON" })


println(resultFunc)
println(resultBlock)
println(resultAnon)

Swift，针对闭包进行了优化

由于Swift针对异步开发进行了优化，苹果在闭包方面投入了更多精力。 首先，函数签名可以被推断出来，所以你不必重写它。

通过数字访问参数

let resultShortAnon = test({return "ANON_" + $0 + "__ANON" })

带有命名的参数推断

let resultShortAnon2 = test({myParam in return "ANON_" + myParam + "__ANON" })

后关闭

只有当block是最后一个参数时，这种特殊情况才有效，它被称为尾随闭包

下面是一个例子(与推断签名合并以显示Swift的能力)

let resultTrailingClosure = test { return "TRAILCLOS_" + $0 + "__TRAILCLOS" }

最后:

使用所有这些功能，我要做的是混合尾随闭包和类型推断(为可读性而命名)

PFFacebookUtils.logInWithPermissions(permissions) {
    user, error in
    if (!user) {
        println("Uh oh. The user cancelled the Facebook login.")
    } else if (user.isNew) {
        println("User signed up and logged in through Facebook!")
    } else {
        println("User logged in through Facebook!")
    }
}

您可以遵循下面的格式，并在类中使用testingObjectiveCBlock属性。

typedef void (^testingObjectiveCBlock)(NSString *errorMsg);

@interface MyClass : NSObject
@property (nonatomic, strong) testingObjectiveCBlock testingObjectiveCBlock;
@end

更多信息请看这里