iOS：在后台使用运行方法的 For 循环？

Question

我有一个 id 数组，其中我运行一个 for 循环，并在后台调用一个运行s 的方法（进行网络调用以获取数据）。我如何知道 for 循环何时结束以及所有调用何时结束？

目前 for 循环在所有预期的调用完成之前完成。我应该使用 while 循环吗？

更新（终于成功了！）

我已将我的代码发布在这里，希望它能对其他人有所帮助。 :)

详细信息：按照 Andrey 的建议，我做的第一件事是继承 NSOperation 并执行以下操作：

@interface AsyncOperation ()

@property (atomic, assign) BOOL _executing;
@property (atomic, assign) BOOL _finished;

@end

@implementation AsyncOperation

- (void)start {

    if ([self isCancelled]) {

        //Move the operation to the finished state if it is canceled.
        [self willChangeValueForKey:@"isFinished"];
        self._finished = YES;
        [self didChangeValueForKey:@"isFinished"];
        return;
    }

    //If the operation is not canceled, begin executing the task.
    [self willChangeValueForKey:@"isExecuting"];
    [NSThread detachNewThreadSelector:@selector(main) toTarget:self withObject:nil];
    self._executing = YES;
    [self didChangeValueForKey:@"isExecuting"];

}

- (void)main {
    if ([self isCancelled]) {
        return;
    }
}

- (BOOL)isAsynchronous {
    return YES;
}

- (BOOL)isExecuting {
    return self._executing;
}

- (BOOL)isFinished {
    return self._finished;
}

//Make sure to expose this method in the header file
- (void)completeOperation {

    [self willChangeValueForKey:@"isFinished"];
    [self willChangeValueForKey:@"isExecuting"];

    self._executing = NO;
    self._finished = YES;

    [self didChangeValueForKey:@"isExecuting"];
    [self didChangeValueForKey:@"isFinished"];
}

最后，在我的方法中我做了：

    //Setup NSOperation Queue
    self.queue = [[NSOperationQueue alloc] init];
    self.queue.name = @"myQueue";

    //Set Queue Observer (Using Third Party Library KVOController)
    [self.KVOController observe:self.queue keyPath:@"operationCount" options:NSKeyValueObservingOptionOld|NSKeyValueObservingOptionNew block:^(id observer, NSOperationQueue *queue, NSDictionary *change) {

        //Check if all operations concluded
        if (queue.operationCount == 0) {

            //Remove Observer
            [self.KVOController unobserve:self.queue];

            //DO SOMETHING NOW THAT EVERYTHING IS DONE
        }
    }];

    //Loop through my chats and fetch each one
    for (NSString *chatId in chatIds) {

        //Observe Operation
        AsyncOperation *operation = [[AsyncOperation alloc] init];
        [self.KVOController observe:operation keyPath:@"isExecuting" options:NSKeyValueObservingOptionNew block:^(id observer, EMKAsyncOperation *myOperation, NSDictionary *change) {

            //Check if operation is executing
            if ([myOperation isExecuting]) {

                //Fetch Chat (My async method)
                [self fetchChatWithId:chatId inBackgroundWithBlock:^(Chat *chat, BOOL succeeded, NSError *error) {

                    //Check for error
                    if (!error) {

                        //DO WHATEVER I DO AFTER FETCHING COMPLETED

                        //Complete operation manually 
                        [myOperation completeOperation];

                        //Remove Observer
                        [self.KVOController unobserve:myOperation];

                    } else {

                       //Error Cancel Everything
                       finalError = error;

                       NSLog(@"Error fetching all chats: %@", [error localizedDescription]);

                       //Cancel Operations
                       [self.queue cancelAllOperations];

                        //Complete operation
                        [myOperation completeOperation];

                        //Remove Observer
                        [self.KVOController unobserve:myOperation];
                    } 
                }];
            }
        }];

        //Add Operation
        [self.queue addOperation:operation];
    }

希望这对人们有所帮助！

Answer 1

问题似乎不在于找出循环何时结束，这是显而易见的，而在于所有网络调用何时结束。所以这就是我要做的。我会将每个网络调用包装到 NSOperation class 的实例中，并将每个操作添加到 NSOperationQueue 中。此 class 具有 operationsCount 属性，这是可观察的键值。所以使用 KVO 你可以观察到这个属性的变化。一旦 operationsCount 等于 0 - 你就完成了。所有请求已完成

Answer 2

创建一个整数变量并在调用完成块时递增它。这样，您就可以了解收到了多少回复。如果该计数 == array.count，则已收到所有响应。

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