iOS 取消GCD的延时操作

GCD的延时操作

我们经常在使用CGD延时之后，一般无法取消，苹果没有提供相对应的api接口，我们通过对GCD的封装来取消延时。
下面我们直接上代码：

typedef void(^SMDelayedBlockHandle)(BOOL cancel);

static SMDelayedBlockHandle perform_block_after_delay(CGFloat seconds, dispatch_block_t block) {
	
	if (nil == block) {
		return nil;
	}
	
	__block dispatch_block_t blockToExecute = [block copy];
	__block SMDelayedBlockHandle delayHandleCopy = nil;
	//我们新建一个block回调，当延迟操作完成时，让GCD走这个回调，我们可以控制这个回调的取消。
	SMDelayedBlockHandle delayHandle = ^(BOOL cancel){		
		if (NO == cancel && nil != blockToExecute) {
			dispatch_async(dispatch_get_main_queue(), blockToExecute);
		}
		
		blockToExecute = nil;
		delayHandleCopy = nil;
	};

    delayHandleCopy = [delayHandle copy];
	dispatch_after(dispatch_time(DISPATCH_TIME_NOW, seconds * NSEC_PER_SEC), dispatch_get_main_queue(), ^{
		if (nil != delayHandleCopy) {
			delayHandleCopy(NO);
		}
	});

	return delayHandleCopy;
};

//我们使用perform_block_after_delay方法进行延迟处理，_delayedBlockHandle负责控制取消延迟的操作
__block SMDelayedBlockHandle blockHandle = _delayedBlockHandle;
_delayedBlockHandle = perform_block_after_delay(2.0f, ^{
            blockHandle = nil;
});

//我们使用这个方法就可以取消perform_block_after_delay放发回调
_delayedBlockHandle(YES);