如何在 NSOperationQueue 中设置优先级以在上一个操作完成之前不执行下一个操作?
NSOperationQueue *operationQueue = [[NSOperationQueue alloc] init];
[operationQueue setMaxConcurrentOperationCount:1];
NSInvocationOperation *operation = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(addPhotoWithButton:) object:button];
[operationQueue addOperation:operation];
[operation release];