ios - Concurrent NSOperation 以及如何设置 isFinished 和 isExecuting？

Question

我正在尝试使用 NSOperations 拆分我的程序流。我正在使用 Parse 框架制作一个简单的消息传递应用程序。我想显示一些消息，然后删除它们。除非删除操作完成，否则不应调用显示消息，因此我想尝试使用 NSQueue 并向其添加 displayMessages 操作，然后添加 deleteMessages 操作(下面名为 MyOperation)。我知道并发操作意味着它们只会以队列方式一个接一个地执行。下面是我的删除方法代码。有没有办法手动告诉操作已完成，即设置 isFinished 或 isExecuting？？

// MyOperation.h
@interface MyOperation : NSOperation {
@property (strong, nonatomic) NSMutableArray *toDelete;
}
@end
And the implementation:

// MyOperation.m
@implementation MyOperation


- (id)initWithArray:(NSMutableArray *)array
{
    self = [super init];
    if (self == nil)
        return nil;

    _toDelete=array;

}

- (void)main {
    if ([self isCancelled]) {
        NSLog(@"** operation cancelled **");
    }



//how do I get main to finish execution ONLY after deleteAllInBackground has finished? 


[PFObject deleteAllInBackground:self.toDelete];

    if ([self isCancelled]) {
        NSLog(@"** operation cancelled **");
    }


    NSLog(@"Operation finished");
}


@end

现在上面这段代码不能解决我的问题。它会将操作排队，但即使 deleteAllInBackground 仍在运行，这个操作也会完成。真的很感谢这里的帮助!谢谢

---

其他可能的解决方案:

-(void)receivedMessage
{
    NSLog(@"push!");
    dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(void){
        [self displayMessages];
        dispatch_async(dispatch_get_main_queue(), ^(void){
            if([self.toDelete count]>0) {
                [PFObject deleteAllInBackground:self.toDelete];

            }


        });
    });



}

Answer 1

我建议你像下面这样使用dispatch_async；

dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(void){
    dispatch_async(dispatch_get_main_queue(), ^(void){
        // Display messages
    });
    // Delete messages here
});

如果您必须使用NSOperationQueue，那么我建议您使用KVO 来获取任务完成的通知；设置队列时，请执行以下操作:

[self.deleteQueue addObserver:self forKeyPath:@"delete-operations" options:0 context:NULL];

然后在您的 observeValueForKeyPath 中执行此操作:

- (void) observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object 
                     change:(NSDictionary *)change context:(void *)context {
    if (object == self.deleteQueue && [keyPath isEqualToString:@"delete-operations"]) {
        if ([self.queue.operations count] == 0) {
            // Delete operation done
            // Display messages here
        }
    } else {
        [super observeValueForKeyPath:keyPath ofObject:object 
                           change:change context:context];
     }
}

[编辑]

-(void)receivedMessage {
@synchronized(self) {
    NSLog(@"push!");
    dispatch_async(dispatch_get_main_queue(), ^(void) {
        [self displayMessages];
        dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(void) {
            if([self.toDelete count]>0) {
                // this deletion doesn't matter if background or on main thread as it's already in background queue
                [PFObject deleteAllInBackground:self.toDelete];
            }
        });
    });
}
}