iOS - dispatch

.h // dispatch_after取消操作 typedef void(^DelayedBlockHandle)(BOOL cancel); DelayedBlockHandle perform_block_after_delay(CGFloat seconds, dispatch_block_t block); void cancel_delayed_block(DelayedBlockHandle delayedHandle); .m DelayedBlockHandle perform_block_after_delay(CGFloat seconds, dispatch_block_t block) { if (nil == block) { return nil; } // block is likely a literal defined on the stack, even though we are using __block to allow us to modify the variable // we still need to move the block to the heap with a copy __block dispatch_block_t blockToExecute = [block copy]; __block DelayedBlockHandle delayHandleCopy = nil; DelayedBlockHandle delayHandle = ^(BOOL cancel){ if (NO == cancel && nil != blockToExecute) { dispatch_async(dispatch_get_main_queue(), 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_main_queue(), ^{ if (nil != delayHandleCopy) { delayHandleCopy(NO); } }); return delayHandleCopy; }; void cancel_delayed_block(DelayedBlockHandle delayedHandle) { if (nil == delayedHandle) { return; } delayedHandle(YES); } 调用 @property (nonatomic, assign) DelayedBlockHandle delayedBlockHandle; _delayedBlockHandle = perform_block_after_delay(秒数, ^{ // 执行内容 }); 取消 cancel_delayed_block(_delayedBlockHandle);