IOS dispatch_after的执行和取消

// dispatch_after 的执行

static PDDelayedBlockHandle perform_block_after_delay(CGFloat seconds, dispatch_block_t block) {  
    if (block == nil) {  
        return nil;  
    }  
      
    __block dispatch_block_t blockToExecute = [block copy];  
    __block PDDelayedBlockHandle delayHandleCopy = nil;  
      
    PDDelayedBlockHandle delayHandle = ^(BOOL cancel) {  
        if (!cancel && blockToExecute) {  
            blockToExecute();  
        }  
          
        // Once the handle block is executed, canceled or not, we free blockToExecute and the handle.  
        // Doing this here means that if the block is canceled, we aren't holding onto retained objects for any longer than necessary.  
#if !__has_feature(objc_arc)  
        [blockToExecute release];  
        [delayHandleCopy release];  
#endif  
          
        blockToExecute = nil;  
        delayHandleCopy = nil;  
    };  
    // delayHandle also needs to be moved to the heap.  
    delayHandleCopy = [delayHandle copy];  
      
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, seconds * NSEC_PER_SEC), dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{  
        if (nil != delayHandleCopy) {  
            delayHandleCopy(NO);  
        }  
    });  
      
    return delayHandleCopy;  
}  

// dispatch_after 的取消 

static void cancel_delayed_block(PDDelayedBlockHandle delayedHandle) {  
    if (nil == delayedHandle) {  
        return;  
    }  
      
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{  
        delayedHandle(YES);  
    });  
}  

调用：

@property (nonatomic, assign) PDDelayedBlockHandle delayedBlockHandle;

// 执行
_delayedBlockHandle = perform_block_after_delay(秒数, ^{  
	 // 执行内容  
 });  

// 取消
cancel_delayed_block(_delayedBlockHandle);