我已经检查并应用了所有可能的答案，但没有成功，因为我找不到原因。     我正在调用一个API，有时它可以正常工作，但是有时它却给我“操作无法完成（nsurlerrordomain错误-1012）”错误。

My API calling code:

我已经创建了此全局方法来调用API。为此，我创建了一个单例课程。

    -(void)getDispatchDetail:(NSString *)strDispatchId successBlock:(void(^)(NSDictionary *response))successBlock withFailureBlock:(FailureBlock)failureBlock{
    NSString *urlString = [NSString stringWithFormat:@"%@%@",BASE_URL,END__POINT_getDispatchDetail];

    [self MethodType:POST URL:urlString parameters:@{@"DispatchId":strDispatchId?strDispatchId:@""} withCookies:nil completionBlockWithSuccess:^(id responseObject,NSURLResponse *urlResponse) {

        successBlock(responseObject);
    } failure:^(NSError *error) {
        [ProgressHUD dismiss];
        failureBlock(error);
    }];
}

    -(void)MethodType:(METHOD_TYPE)methodType
              URL:(NSString *)urlString
       parameters:(NSDictionary *)param
      withCookies:(BOOL)isCookies completionBlockWithSuccess:(void (^)(id responseObject,NSURLResponse *urlResponse))success
          failure:(void (^)(NSError *error))failureRequest
{
    if (isCookies){
        //[ProgressHUD show:kSTRING_LOADING Interaction:NO];
    }
    /**
     Create URl based on the Request Type
     **/
    NSURL *url;
    switch (methodType) {
        case GET:
            if (param) {
                NSString *strDict   =   [self stringFromDictionary:param];
                NSString *strURL    =   [NSString stringWithFormat:@"%@?%@",urlString,strDict];
                strURL              =   [strURL stringByReplacingOccurrencesOfString:@" " withString:@"%20"];
                url                 =   [NSURL URLWithString:strURL];
                break;
            }
            url                     =   [NSURL URLWithString:urlString];
            break;
        case PUT:
        case POST:
        case DELETE:
            url = [NSURL URLWithString:urlString];
            break;
        default:
            break;
    }

    /**
     Create Reuqest based on the Request Type
     **/
    NSMutableURLRequest *req = [NSMutableURLRequest requestWithURL:url];

    switch (methodType) {
        case GET:
            [req setHTTPMethod:@"GET"];
            break;

        case POST:
        {
            [req setHTTPMethod:@"POST"];
            NSError *error = nil;

            NSData *postData = [NSJSONSerialization dataWithJSONObject:param options:NSJSONWritingPrettyPrinted error:&error];
            if (error) {
                failureRequest(error);
            }

            [req setvalue:@"application/json" forHTTPHeaderField:@"Content-Type"];
            [req setHTTPBody:postData];
        }
            break;

        case PUT:
        {
            [req setHTTPMethod:@"PUT"];
            NSError *error = nil;
            if (param != nil) {
                NSData *postData = [NSJSONSerialization dataWithJSONObject:param options:NSJSONWritingPrettyPrinted error:&error];
                [req setHTTPBody:postData];
            }
            if (error) {
                failureRequest(error);
            }

            [req setvalue:@"application/json" forHTTPHeaderField:@"Content-Type"];

        }
            break;

        case DELETE:
        {
            [req setHTTPMethod:@"DELETE"];
        }
            break;
        default:
            break;
    }

    //self.straccessToken = @"Token ab6520a0805b11e82c750034548b74d02464e900";
    //self.straccessToken = [ETDataModelClass getUseraccessToken];

    if ([[NSUserDefaults standardUserDefaults] valueForKey:API_PARAM_USER_accESS_TOKEN] != nil) {
        NSDictionary *dict = [[NSUserDefaults standardUserDefaults] objectForKey:kUserLoginTokenAndData];
        NSString *tokenType = [dict objectForKey:@"token_type"];

        self.straccessToken = [NSString stringWithFormat:@"%@ %@",tokenType,[[NSUserDefaults standardUserDefaults] valueForKey:API_PARAM_USER_accESS_TOKEN]];

        // [self.straccessToken stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
        [req setvalue:self.straccessToken forHTTPHeaderField:API_accESS_TOKEN];
    }
    NSLog(@"ReqType : %@ URL : %@,Param : %@",[self getMethodTypeName:methodType],url,param);
    NSLog(@"User Token : %@",_straccessToken);
    [req setTimeoutInterval:60.0];

    [NSURLConnection sendAsynchronousRequest:req
                                       queue:[NSOperationQueue mainQueue]
                           completionHandler:^(NSURLResponse *responseHeader,NSData *responseBody,NSError *error)
     {
         NSError *errordata = nil;
         NSLog(@"Response Header : %@",responseHeader);
         NSLog(@"Response : %@",[[NSString alloc] initWithData:responseBody encoding:NSUTF8StringEncoding]);
         id responseObject1;
         if(![responseBody isKindOfClass:[Nsnull class]] && responseBody != nil)
           responseObject1 = [NSJSONSerialization JSONObjectWithData:responseBody options:NSJSONReadingMutableLeaves error:&errordata];
         else{
             [ProgressHUD dismiss];
             [Utility showAlertMessage:@"No Internet Connection. Make sure your device is connected to the internet." WithTitle:@""];
             return ; // When response body nil we will return the control
         }
//         NSLog(@"Server Response ===> :\n %@",responseObject1);
//         NSLog(@"Server Error ===> :\n %@",errordata);

         if (error)  {
             if([responseObject1 isKindOfClass:[NSDictionary class]]){
                 if([[responseObject1 objectForKey:API_Alert_MESSAGE] isEqualToString:kAutologoutResponseFromServer]){

                     NSLog(@" Response ===== %@  =====",responseObject1);
                     [[NsnotificationCenter defaultCenter] postNotificationName:kNotificationAutoLogout object:nil userInfo:responseObject1];
                 }
             }
             [ProgressHUD dismiss];
             failureRequest(error);
             return ;
         }
         else {
             //[ProgressHUD dismiss];

             if (!errordata) {
                 if (responseObject1 == nil) {
                     return [Utility showAlertMessage:NO_DATA_AVAILABLE WithTitle:@""];
                 }
                 NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *) responseHeader;
                 long statusCode = httpResponse.statusCode;
                 NSLog(@"statusCode : %ld",statusCode);
                 switch (statusCode) {
                     case API_STATUS_CODE_200: case API_STATUS_CODE_402:
                         if (success) {
                             success(responseObject1,responseHeader);
                         }
                         break;

                     case API_STATUS_CODE_500:  case API_STATUS_CODE_400:
                         NSLog(@"responseHeader : %@",responseHeader);
                         NSLog(@"responseBody : %@",[[NSString alloc] initWithData:responseBody encoding:NSUTF8StringEncoding]);
                         NSLog(@"error : %@",error.localizedDescription);
                         NSLog(@"%@",[[NSString alloc] initWithData:responseBody encoding:NSUTF8StringEncoding]);

                           [Utility showAlertMessage:SERVER_ERROR WithTitle:@""];
                         [ProgressHUD dismiss];
                         break;
                     case API_STATUS_CODE_403:{
                         NSLog(@"auto logout warning  : %@",responseBody);
                         [[NsnotificationCenter defaultCenter] postNotificationName:kNotificationAutoLogout object:nil userInfo:responseObject1];
                         [ProgressHUD dismiss];
                         break;
                     }
                     default:
                         NSLog(@"responseHeader : %@",[[NSString alloc] initWithData:responseBody encoding:NSUTF8StringEncoding]);
                         if([responseObject1 isKindOfClass:[NSDictionary class]])
                             if([responseObject1 valueForKey:API_Alert_MESSAGE] && [responseObject1 valueForKey:API_Alert_MESSAGE] != nil)
                             [Utility showAlertMessage:[responseObject1 valueForKey:API_Alert_MESSAGE] WithTitle:@""];
                         [ProgressHUD dismiss];
                         break;
                 }
             }
             else{
                 failureRequest(errordata);
             }
         }
     }];
}