如何同步两个 NSURLSessionDataTask？答案

【问题标题】：How to synchronize two NSURLSessionDataTasks?如何同步两个 NSURLSessionDataTask？
【发布时间】：2014-12-12 13:42:15
【问题描述】：

我不知道如何同步 NSURLSessionDataTask。

如何在 syncInfo1Info2 中同步这两个会话：

- (void) syncInfo1Info2
{
  //How do I sync???
}

- (void) getSomeInfo1
{
NSString *stringToUrl = [[NSString alloc]initWithFormat:@"url"];
NSURLSession *session = [NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration]];
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:[stringToUrl stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]]];
NSURLSessionDataTask *task =[session dataTaskWithRequest: request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error){
    //Some code...

        }];
[task resume];
}

- (void) getSomeInfo2
{
NSString *stringToUrl = [[NSString alloc]initWithFormat:@"url"];
NSURLSession *session = [NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration]];
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:[stringToUrl stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]]];
NSURLSessionDataTask *task =[session dataTaskWithRequest: request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error){
   //Some code...

}];
[task resume];
}

【问题讨论】：

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标签： ios objective-c xcode concurrency

【解决方案1】：

像这样：

dispatch_group_t group = dispatch_group_create();

- (void) syncInfo1Info2
{
  [self getSomeInfo1];
  [self getSomeInfo2];
  dispatch_group_notify(group, dispatch_get_main_queue(), ^{
     //both tasks have been processed
  });
}

- (void) getSomeInfo1
{
    dispatch_group_enter(group);
    NSString *stringToUrl = [[NSString alloc]initWithFormat:@"url"];
    NSURLSession *session = [NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration]];
    NSMutableURLRequest *requestRu = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:[stringToUrl stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]]];
    NSURLSessionDataTask *task =[session dataTaskWithRequest: requestRu completionHandler:^(NSData *data, NSURLResponse *response, NSError *error){
        NSError *err;
        dispatch_group_leave(group);
        }];
    [task resume];
}

- (void) getSomeInfo2
{
    dispatch_group_enter(group);
    NSString *stringToUrl = [[NSString alloc]initWithFormat:@"url"];
    NSURLSession *session = [NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration]];
    NSMutableURLRequest *requestRu = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:[stringToUrl stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]]];
    NSURLSessionDataTask *task =[session dataTaskWithRequest: requestRu completionHandler:^(NSData *data, NSURLResponse *response, NSError *error){
        NSError *err;
        dispatch_group_leave(group);
    }];
    [task resume];
}

【讨论】：

【解决方案2】：

你可以使用NSOperationQueue在操作之间添加依赖的简单方法

例如。

NSOperationQueue  *operationQueue = [[NSOperationQueue alloc] init];

NSBlockOperation *downloadOperation1 = [[NSBlockOperation alloc] init];
 __weak NSBlockOperation *weakOperation1 = downloadOperation1;

[weakOperation1 addExecutionBlock:^{
    [self getSomeInfo1];
}];


NSBlockOperation *downloadOperation2 = [[NSBlockOperation alloc] init];
__weak NSBlockOperation *weakOperation2 = downloadOperation2;

[weakOperation2 addExecutionBlock:^{
    [self getSomeInfo2];
}];

[downloadOperation2  addDependency:downloadOperation1];
[operationQueue addOperation:downloadOperation1];
[operationQueue addOperation:downloadOperation2];

或者使用这个link中给出的方法

在 HTTPMaximumConnectionsPerHost 属性设置为 1 的类中创建 NSURLSession 单例：

+ (NSURLSession *)session
{
    static NSURLSession *session = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{

        NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration];

        [configuration setHTTPMaximumConnectionsPerHost:1];

        session = [NSURLSession sessionWithConfiguration:configuration];

    });
    return session;
}

然后使用

NSURLSessionDataTask *dataTask = 
[[[self class] session] dataTaskWithURL:url 
                          completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
}
[dataTask resume]

【讨论】：

【解决方案3】：

我们可以将 api gunc 放在一个类中并在其上创建一个共享实例，在视图控制器类中我们可以像这样调用类实例

ApiClient.shared.api1() ApiClient.shared.api2()

由于我们有一个共享实例，所以 api 调用将被同步

【讨论】：