iOS進階——可取消的block

標籤：

+ (id)performBlock:(void (^)())aBlock onQueue:(dispatch_queue_t)queue afterDelay:(NSTimeInterval)delay{    NSParameterAssert(aBlock != nil);    __block BOOL cancelled = NO;    void (^wrapper)(BOOL) = ^(BOOL cancel){        if (cancel) {            cancelled = YES;            return;        }        if (!cancelled) {            aBlock();        }    };    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delay * NSEC_PER_SEC)), queue, ^{        wrapper(NO);    });    return [wrapper copy];}+ (void)cancelBlock:(id)aBlock{    NSParameterAssert(aBlock != nil);    void (^wrapper)(BOOL) = aBlock;    wrapper(YES);}

 

iOS進階——可取消的block