GCD ：
dispatch_queue_t serielQueue = dispatch_queue_create("myQueue", DISPATCH_QUEUE_SERIAL);
dispatch_sync(serielQueue, ^{
[self loadDetailData]; //请求A
});
dispatch_sync(serielQueue, ^{
[self loadHotCommentData]; //请求B
});
dispatch_sync(serielQueue, ^{
[self loadOtherCommentData]; //请求C
});
dispatch_sync(serielQueue, ^{
[self loadPhotoData]; //请求D
});
------------------------------分割线-----------------------------------
NSOperationQueue ：
// 创建一个队列
NSOperationQueue *queue = [[NSOperationQueue alloc]init];
// 设置最大线程数
queue.maxConcurrentOperationCount = 1;
// 创建一个A操作
NSBlockOperation *operationA = [NSBlockOperation blockOperationWithBlock:^{
[self loadDetailData];
}];
// 创建一个B操作
NSBlockOperation *operationB = [NSBlockOperation blockOperationWithBlock:^{
[self loadHotCommentData];
}];
// 创建一个C操作
NSBlockOperation *operationC = [NSBlockOperation blockOperationWithBlock:^{
[self loadOtherCommentData];
}];
// 创建一个D操作
NSBlockOperation *operationD = [NSBlockOperation blockOperationWithBlock:^{
[self loadPhotoData];
}];
/ /添加依赖
[operationB addDependency:operationA];
[operationC addDependency:operationB];
[operationD addDependency:operationC];
// 分别加入到队列中
[queue addOperation:operationA];
[queue addOperation:operationB];
[queue addOperation:operationC];
[queue addOperation:operationD];