get请求返回的是字符串，将其改成字典

(void)loginBtnClick:(id)sender{
    

    AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];
    manager.responseSerializer = [AFHTTPResponseSerializer serializer];
    
    NSString *str = @"http://xxxx/pay_user/Login"; //对应的后台的地址。
    
    NSDictionary *dict = @{@"APPID":@"10086",@"username": @"admin",@"password":@"admin"};
//    NSDictionary *dict = @{@"APPID":corporateTextField.text,@"username": phoneNumTextField.text,@"password":passwordTextField.text};
    
    [manager GET:str parameters:dict success:^(AFHTTPRequestOperation *operation, id responseObject) {
        
       <span style="color:#ff0000;"> NSDictionary *dict = [NSJSONSerialization JSONObjectWithData:responseObject options:NSJSONReadingMutableContainers error:nil];  //主要是要加入这句话，不加入的话，返回的是一串字符串，如果加入的话，就能够正常的将数据当做字典使用。</span>
        
        NSLog(@"服务器返回的数据是：%@",responseObject);
        NSLog(@"加入字典解析的数据是:%@",dict);

        NSString *logid = dict[@"log_id"];
        NSString *isLogin = dict[@"isLogin"];
        
        if ([isLogin isEqualToString:@"3"]) {
            
            FirstViewController *firstVC = [[FirstViewController alloc] init];
            firstVC.log_iD = logid;
            [self.navigationController pushViewController:firstVC animated:YES];
        }
    
    } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
        
        NSLog(@"请求失败了  %@",error.localizedDescription);
        
    }];
}