exception throw :'data parameter is nil', 在 iOS 中访问 HTTP Web 服务时发生错误？

Question

我是 iPhone 应用程序开发的新手，在进行 API 调用时很少遇到以下错误。大多数时候我从服务器服务器得到正确的响应。但有时我会遇到以下错误。我检查了 URL 没有错误。 在此先感谢。，任何人都可以分享您在没有此错误的情况下访问 API 调用的知识。

这是我的代码

-(void)callUserAPI {

    arrList = nil;

    NSString *targetUrl;

    //    if ([[dict valueForKey:@"user_id"] isEqualToString:@"1"])
    //        targetUrl = [NSString stringWithFormat:@"%@index.php/restapi/chats?limit=%@",[dict valueForKey:@"support_location"],@"1000"];
    //    else
    targetUrl = [NSString stringWithFormat:@“https://yoururl”,[dict valueForKey:@"support_location"],@"1000"];

    NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];

    NSString *authStr = [NSString stringWithFormat:@"%@:%@", [dict valueForKey:@"username"], [dict valueForKey:@"password"]];

    NSData *authData = [authStr dataUsingEncoding:NSUTF8StringEncoding];

    NSString *authValue = [NSString stringWithFormat:@"Basic %@", [authData base64Encoding]];

    [request addValue:authValue forHTTPHeaderField:@"Authorization"];

    [request addValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"];

    NSLog(@"%@",request.allHTTPHeaderFields);

    [request setHTTPMethod:@"GET"];

    [request setURL:[NSURL URLWithString:targetUrl]];

    [[[NSURLSession sharedSession] dataTaskWithRequest:request completionHandler:
      ^(NSData * _Nullable data,

        NSURLResponse * _Nullable response,

        NSError * _Nullable error) {


             NSDictionary *responseDictionary = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingAllowFragments error:&error];

             self->arrList = [[NSMutableArray alloc] init];
             self->arrPending = [[NSMutableArray alloc] init];
             self->arrActive = [[NSMutableArray alloc] init];
             self->arrClosed = [[NSMutableArray alloc] init];

             self->arrList =[responseDictionary valueForKey:@"list"];

             // 0 - pending, 1 - active, 2 - closed chat,

             for (NSDictionary *temp in self->arrList) {


                 if ([[temp valueForKey:@"status"] intValue] == 1 ) {
                     if (!([[self->dict valueForKey:@"user_id"] intValue] == 1) ) {
                         if ([[temp valueForKey:@"user_id"] intValue] == [[self->dict valueForKey:@"user_id"] intValue]) {
                             [self->arrActive addObject:temp];
                         }
                     }else{
                         [self->arrActive addObject:temp];
                     }
                 }
                 else if ([[temp valueForKey:@"status"] intValue] == 2 ) {
                     if (!([[self->dict valueForKey:@"user_id"] intValue] == 1) ) {
                         if ([[temp valueForKey:@"user_id"] intValue] == [[self->dict valueForKey:@"user_id"] intValue]) {
                             [self->arrClosed addObject:temp];
                         }
                     }else{
                         [self->arrClosed addObject:temp];
                     }
                 }else if ([[temp valueForKey:@"status"] intValue] == 0 ) {

                     [self->arrPending addObject:temp];

                 }




                 //            if ([dict valueForKey:@"user_id"] == [temp valueForKey:@"user_id"]) {
                 //                if ([[temp valueForKey:@"status"] intValue] == 0) {
                 //                    [self->arrPending addObject:temp];
                 //                }else if([[temp valueForKey:@"status"] intValue] == 1) {
                 //                    [self->arrActive addObject:temp];
                 //                }else if([[temp valueForKey:@"status"] intValue] == 2) {
                 //                    [self->arrClosed addObject:temp];
                 //                }else{
                 //
                 //                }
                 //            }


             }


             dispatch_async(dispatch_get_main_queue(), ^{

                 self->_lblActiveCount.text = [NSString stringWithFormat:@"%lu",(unsigned long)self->arrActive.count];
                 self->_lblPendingCount.text = [NSString stringWithFormat:@"%lu",(unsigned long)self->arrPending.count];
                 self->_lblClosedCount.text = [NSString stringWithFormat:@"%lu",(unsigned long)self->arrClosed.count];

                 [self->_tblView reloadData];

                 [self->HUD hide:YES];
             });


      }] resume];
}

每当我的应用程序从后台转到前台时，我都会得到这样的结果。

2019-06-19 16:53:56.366971+0530 LiveTracker[523:62321] TIC TCP 连接 失败 [122:0x282b77540]: 1:53 Err(53) 2019-06-19 16:53:56.367912+0530 LiveTracker[523:62321] 任务 . HTTP 加载失败（错误 代码：53 [1:53]) 2019-06-19 16:53:56.374704+0530 LiveTracker[523:62264] 任务 . 以错误结束 - 代码：53 2019-06-19 16:53:56.378241+0530 LiveTracker[523:62305] * 由于未捕获的异常而终止应用程序 'NSInvalidArgumentException'，原因：'数据参数为零' * 第一次抛出调用栈：(0x1b76ac518 0x1b68879f8 0x1b75b6c70 0x1b8046390 0x100c7b65c 0x1b7c80688 0x1b7c94220 0x1b8110f68 0x1b801d420 0x1b801c908 0x1b8112cec 0x10141f6f0 0x101420c74 0x101423ffc 0x101423458 0x101431dc8 0x1014327ac 0x1b72cd1b4 0x1b72cfcd4) libc++abi.dylib: 以未捕获的异常终止 输入 NSException

Answer 1

错误很可能是由以下原因产生的：

NSDictionary *responseDictionary = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingAllowFragments error:&error];

这是因为有时 Web 请求会失败，原因可能是超时、连接错误，甚至只是 Web 会话过期。无论错误的原因是什么，在假设您有数据要解析之前，您都必须检查 API 请求是成功还是失败。

至少检查data 在您的回调处理程序中是否为零。