如何获取数据以从 NSURLSessionDataTask 返回

Question

我有一个注册视图控制器，它处理所有用户输入并调用另一个类 (wsClass) 中的函数传递给它，该数据作为 NSDictionary。

调用 wsClass 中的函数并建立连接并从服务器返回数据并在会话中可用。

我的问题是如何将该数据返回到最初调用该函数的注册视图控制器，它总是空的。

这是registrationViewController中的调用：

        wsClass *ws = [[wsClass alloc] init];
    NSDictionary *testDict = [[NSDictionary alloc] initWithObjectsAndKeys:username.text,@"username",email.text,@"email",password.text,@"password", nil];
    NSDictionary *respDict = [ws sendData:testDict];

这是 wsClass.m 中调用的函数：

- (NSDictionary *)sendData:(NSDictionary *)sendDict {
NSMutableString *sendStr = [[NSMutableString alloc] init];

[sendDict enumerateKeysAndObjectsUsingBlock:^(id key, id obj, BOOL *stop) {
    [sendStr appendFormat:@"&%@=%@", key, obj];
}];

NSLog(@"sendStr is: %@",sendStr);
NSString *noteDataString = [NSString stringWithFormat:@"%@%@",REQUIRED,sendStr];

NSURLSessionConfiguration *sessionConfiguration = [NSURLSessionConfiguration defaultSessionConfiguration];
NSURLSession *session = [NSURLSession sessionWithConfiguration:sessionConfiguration];
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:urlTest]];
request.HTTPBody = [noteDataString dataUsingEncoding:NSUTF8StringEncoding];
request.HTTPMethod = @"POST";

NSURLSessionDataTask *postDataTask = [session dataTaskWithRequest:request
                                                completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
                                                    // The server answers with an error because it doesn't receive the params
                                                    // handle response
                                                    if(error == nil)
                                                    {
                                                        [getReqAlert dismissWithClickedButtonIndex:0 animated:YES];

                                                        NSError *e = nil;
                                                        jsonArray = [NSJSONSerialization JSONObjectWithData: data options: NSJSONReadingMutableLeaves error: &e];

                                                        if (!jsonArray) {
                                                            NSLog(@"Error parsing JSON: %@", e);
                                                        } else {

                                                            NSLog(@"resp: %@ = %@",[jsonArray objectForKey:@"status"],[jsonArray objectForKey:@"msg"]);
                                                            NSLog(@"Dictionary count: %lu", jsonArray.count);
                                                        }
                                                    }
                                                }];

 [postDataTask resume];

return jsonArray;

}

Answer 1

帖子异步完成，因此您的wsClass 需要在帖子完成后告诉调用者完成。一个很好的方法是使用调用者提供的代码块来扩充sendData 方法，该代码块应该在完成时运行：

将sendData: 更改为如下所示：

// it doesn't return anything, because all it does is launch the post
// but when the post is done, it invokes completion

- (void)sendData:(NSDictionary *)sendDict completion:(void (^)(NSDictionary *))completion {

    // the stuff you're already doing

        NSURLSessionDataTask *postDataTask = [session dataTaskWithRequest:request
            completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
            // the stuff you're already doing
            // now tell the caller that you're done
            completion(jsonArray);
        }];
    }

调用者现在看起来像这样：

// change the UI to say "I'm busy doing the post"
[ws sendData:testDict completion:^(NSDictionary *responseDict) {
    NSLog(@"this runs later, after the post completes %@", responseDict);
    // change the UI to say "The post is done"
}];

关于此的几点说明：(1) 我没有在块中添加错误参数，您可能应该这样做。检查并使用 nil 和错误，或使用 json 输出和 error=nil 调用块。 (2) 您的代码假定 json 结果解析为字典。在您在代码中假设它之前，请确保它始终是正确的。 (3) 类名通常以大写字母开头。

Answer 2

您可以使用信号量等待块完成执行，然后从函数返回值

- (NSDictionary *)sendData:(NSDictionary *)sendDict {
NSMutableString *sendStr = [[NSMutableString alloc] init];

[sendDict enumerateKeysAndObjectsUsingBlock:^(id key, id obj, BOOL *stop) {
[sendStr appendFormat:@"&%@=%@", key, obj];
}];

NSLog(@"sendStr is: %@",sendStr);
NSString *noteDataString = [NSString stringWithFormat:@"%@%@",REQUIRED,sendStr];

NSURLSessionConfiguration *sessionConfiguration = [NSURLSessionConfiguration defaultSessionConfiguration];
NSURLSession *session = [NSURLSession sessionWithConfiguration:sessionConfiguration];
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:urlTest]];
request.HTTPBody = [noteDataString dataUsingEncoding:NSUTF8StringEncoding];
request.HTTPMethod = @"POST";


 let semaphore = dispatch_semaphore_create(0)

NSURLSessionDataTask *postDataTask = [session dataTaskWithRequest:request
completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
// The server answers with an error because it doesn't receive the params
// handle response
if(error == nil)
{
[getReqAlert dismissWithClickedButtonIndex:0 animated:YES];

NSError *e = nil;
jsonArray = [NSJSONSerialization JSONObjectWithData: data options: NSJSONReadingMutableLeaves error: &e];

if (!jsonArray) {
NSLog(@"Error parsing JSON: %@", e);
} else {

NSLog(@"resp: %@ = %@",[jsonArray objectForKey:@"status"],[jsonArray objectForKey:@"msg"]);
NSLog(@"Dictionary count: %lu", jsonArray.count);

     dispatch_semaphore_signal(semaphore)
}
}
}];

[postDataTask resume];
 dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER)
return jsonArray;

}

Answer 3

这可能有效。

1. 为 NSDict 或您在类中检索的任何内容添加接口变量 nsDictVariable
2. 在 SendData 中分配它：self.nsDictVariable = ....

Answer 4

试试这个。这会很好用。

-(void)loadDetails
{

NSURLSession *session = [NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration]];
[[session dataTaskWithRequest:request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {


    _allVehicleLocationsArray = [NSJSONSerialization JSONObjectWithData:data options:0 error:nil];

    [self afterCompleteDoThis];


}] resume];


}

-(void)afterCompleteDoThis{

for (NSDictionary *vehicleDict in _allVehicleLocationsArray) {

    NSLog(@" PPP %@" , [vehicleDict valueForKey:@"vehicleType"]);

}
}