等到多个网络请求都执行完毕 - 包括它们的完成块 [英] Wait until multiple networking requests have all executed - including their completion blocks

问题描述

我有多个操作(它们是 AFNetworking 请求)，其中包含需要一些时间来执行的完成块，以及需要在所有请求结束时保存的核心数据对象.

I have multiple operations (they're AFNetworking requests) with completion blocks that takes some time to execute, and a Core Data object that needs to be saved at the end of all the requests.

MyCoreDataObject *coreDataObject;

AFHTTPRequestOperation *operation1 = [[AFHTTPRequestOperation alloc] initWithRequest:request1];
[operation1 setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
    coreDataObject.attribute1 = responseObject;
    sleep(5);
}];
[operation1 start];

AFHTTPRequestOperation *operation2 = [[AFHTTPRequestOperation alloc] initWithRequest:request1];
[operation2 setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
    coreDataObject.attribute2 = responseObject;
    sleep(10);
}];
[operation1 operation2];

[context save:nil];

当然，这不会如我所愿，因为请求是异步的.我尝试添加一个 NSOperationQueue 像这样:

Of course, this does not work as I want because the requests are asynchronous. I tried adding an NSOperationQueue like so:

NSOperationQueue *operationQueue = [[NSOperationQueue alloc] init];
[operationQueue setMaxConcurrentOperationCount:2];

AFHTTPRequestOperation *operation1 = [[AFHTTPRequestOperation alloc] initWithRequest:request1];
[operation1 setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
    coreDataObject.attribute1 = responseObject;
    sleep(5);
}];
[operationQueue addOperation:operation1];

AFHTTPRequestOperation *operation2 = [[AFHTTPRequestOperation alloc] initWithRequest:request1];
[operation2 setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
    coreDataObject.attribute2 = responseObject;
    sleep(10);
}];
[operationQueue addOperation:operation2];

[imageQueue waitUntilAllOperationsAreFinished];
[context save:nil];

这看起来好一点.使用 waitUntilAllOperationsAreFinished，我的队列阻塞当前线程，直到我的请求完成，但直到我的成功块完成，这才是我真正需要的.

This looks a bit better. Using waitUntilAllOperationsAreFinished, my queue blocks the current thread until my requests are finished, but not until my success Blocks are finished, which is really what I need.

关于如何以好的方式实现这一目标的任何想法?

Any ideas on how to achieve this in a good way?

推荐答案

使用调度组.

dispatch_group_t group = dispatch_group_create();

MyCoreDataObject *coreDataObject;

dispatch_group_enter(group);
AFHTTPRequestOperation *operation1 = [[AFHTTPRequestOperation alloc] initWithRequest:request1];
[operation1 setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
    coreDataObject.attribute1 = responseObject;
    sleep(5);
    dispatch_group_leave(group);
}];
[operation1 start];

dispatch_group_enter(group);
AFHTTPRequestOperation *operation2 = [[AFHTTPRequestOperation alloc] initWithRequest:request1];
[operation2 setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
    coreDataObject.attribute2 = responseObject;
    sleep(10);
    dispatch_group_leave(group);
}];
[operation2 start];

dispatch_group_wait(group, DISPATCH_TIME_FOREVER);
dispatch_release(group);

[context save:nil];

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