參考： http://stackoverflow.com/questions/1049001/get-notification-when-nsoperationqueue-finishes-all-tasks

? ? ?多線程編程中，操作隊列NSOperationQueue我們經(jīng)常會用到的，簡化了多線程的操作。至于用法就不多介紹了。這里要說的是隊列執(zhí)行完畢的狀態(tài)檢查。

? ? ? 我們很多時候需要在隊列完成之后再進行操作，而何時隊列完成，NSOperationQueue并沒有內(nèi)置的didFinishedSelector來供使用，因此需要自己去檢查其狀態(tài)。

? ? ? 因為NSOperationQueue兼容?key-value coding (KVC) and key-value observing (KVO)機制，因此我們可以觀察NSOperationQueue的屬性。NSOperationQueue可供監(jiān)控觀察的屬性有：

• operations?- read-only property

• operationCount?- read-only property

• maxConcurrentOperationCount?- readable and writable property

• suspended?- readable and writable property

• name?- readable and writable property

實現(xiàn)如下：

1.初始_parseQueue

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-?(NSOperationQueue?*)parseQueue??

{??

????if?(nil?==?_parseQueue)??

????{??

????????_parseQueue?=?[[NSOperationQueue?alloc]?init];??

????????[_parseQueue?setSuspended:YES];??

????????//[_parseQueue?setMaxConcurrentOperationCount:1];??

????????[_parseQueue?addObserver:self??

??????????????????????forKeyPath:@"operations"??

?????????????????????????options:0??

?????????????????????????context:nil];??

????}??

??????

????return?_parseQueue;??

}??

2.加入operation

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NSInvocationOperation?*operation?=?[[NSInvocationOperation?alloc]?initWithTarget:self??

???????????????????????????????????????????????????????????????????????selector:@selector(myTask)???

?????????????????????????????????????????????????????????????????????????object:nil];??

[self.parseQueue?addOperation:operation];??

[operation?release];<strong>??

rong>??

3.觀察值的改變：

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//KVO,觀察parseQueue是否執(zhí)行完??

-?(void)observeValueForKeyPath:(NSString?*)keyPath??

??????????????????????ofObject:(id)object???

????????????????????????change:(NSDictionary?*)change???

???????????????????????context:(void?*)context??

{??

????if?(object?==?self.parseQueue?&&?[keyPath?isEqualToString:@"operations"])??

????{??

????????if?(0?==?self.parseQueue.operations.count)??

????????{??

????????????DLog(@"parse?finished");??

????????????//other?operation??

????????????[_parseQueue?setSuspended:YES];??

??????????????

????????}??

????}??

????else??

????{??

????????[super?observeValueForKeyPath:keyPath?ofObject:object?change:change?context:context];??

????}??

}??

選擇對NSOperationQueue的operations進行觀察，而不選operationCount是因為operationCount需要iOS 4.0以上

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