android - 使用 HttpWebResponse 时 Xamarin Android 中未处理的异常

Question

我有以下代码:

public async Task<List<RobotViewModel>> GetBot(string token)
    {
        var menulist = new List<RobotViewModel>();
        try
        {
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create("mysite/bot/abc/process/GetBot");
            request.Accept = "application/json";
            request.Method = "GET";
            request.Headers["Authorization"] = "Bearer " + token;
            var response = (HttpWebResponse)await request.GetResponseAsync().ConfigureAwait(false);
            if(response.StatusCode==HttpStatusCode.OK)
            {
                var encoding = ASCIIEncoding.UTF8;
                using (var reader = new System.IO.StreamReader(response.GetResponseStream(), encoding))
                {
                    string responseText = reader.ReadToEnd();
                    menulist = JsonConvert.DeserializeObject<List<RobotViewModel>>(responseText);
                }
            }
        }
        catch(System.Net.WebException exc)
        {
            var response = (HttpWebResponse)exc.Response;
            switch(response.StatusCode)
            {
                case HttpStatusCode.InternalServerError:
                    {
                        _userRepo = await new Repository<User>().MakeDatabaseAsync();
                        var user = await _userRepo.Table.Where(p => p.LoggedIn).FirstOrDefaultAsync();
                        await Login(user.UserName, user.Password);
                        HttpWebRequest request = (HttpWebRequest)WebRequest.Create("mysite/bot/abc/process/GetBot");
                        request.Accept = "application/json";
                        request.Method = "GET";
                        request.Headers["Authorization"] = "Bearer " + user.AccessToken;
                        response = (HttpWebResponse)await request.GetResponseAsync().ConfigureAwait(false);
                        if (response.StatusCode == HttpStatusCode.OK)
                        {
                            var encoding = ASCIIEncoding.UTF8;
                            using (var reader = new System.IO.StreamReader(response.GetResponseStream(), encoding))
                            {
                                string responseText = reader.ReadToEnd();
                                menulist = JsonConvert.DeserializeObject<List<RobotViewModel>>(responseText);

                            }
                        }
                        break;
                    }
                default:
                    throw;
            }
        }
        catch(Exception exc)
        {

        }

        return menulist;
    }

此代码用于以下委托(delegate):

    navigationView.NavigationItemSelected += async delegate
            {

                AndHUD.Shared.Show(this, "Please Wait", -1, AndroidHUD.MaskType.Clear);


                var botList = await client.GetBot(loggedInUser.AccessToken);
                if (botList.Count > 0)
                {
                    var botListMemory = await _botRepo.GetAllAsync();

                    foreach (var item in botList)
                    {
                        var bot =await _botRepo.Table.Where(p => p.Token == item.Token).FirstOrDefaultAsync();
                        if(bot==null)
                        await _botRepo.CreateAsync(new Robot
                        {
                            Name = item.Name,
                            Token = item.Token,
                            TokenUrl = item.TokenUrl,
                            UserId = loggedInUser.Id,
                            Description = item.Description
                        });
                        else
                        {
                            bot.Name = item.Name;
                            bot.Token = item.Token;
                            bot.TokenUrl = item.TokenUrl;
                            bot.UserId = loggedInUser.Id;
                            bot.Description = item.Description;
                            await _botRepo.UpdateAsync(bot);
                        }
                    }

                    AndHUD.Shared.ShowSuccess(this, "Success", MaskType.Clear, TimeSpan.FromSeconds(2));
                }
                else
                    AndHUD.Shared.ShowError(this, "Server Error", MaskType.Clear, TimeSpan.FromSeconds(2));

                SetData(botList, out myAdapter);
                expandableListView.SetAdapter(myAdapter);
            };

当 Bearer token 过期时，catch block 会抛出一个未处理的异常。当我重新运行该程序时，一切正常，因为在之前的应用程序运行时已在 catch block 中生成了新的 Bearer token 。

Answer 1

代码中有很多问题:

1. ConfigureAwait(false) 应该只在类库中使用，因为它会导致当前任务由 threadPool 中的线程处理，而不是主线程...

2. httpClient 应该在 using block 中以将其从 using block 中释放出来。所以我改变了 GetBot 方法如下:

   public async Task<List<RobotViewModel>> GetBot(string token)
   {
       var menulist = new List<RobotViewModel>();
       using (var localClient = new HttpClient())
       {
           try
           {
               localClient.MaxResponseContentBufferSize = 256000;
               localClient.Timeout = TimeSpan.FromSeconds(40);
               localClient.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
               localClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", token);
               var uri = new Uri("mySite/GetBot");
               var response = await localClient.GetAsync(uri);
               if (response.StatusCode == HttpStatusCode.OK)
               {
                   var encoding = ASCIIEncoding.UTF8;
                   using (var reader = new System.IO.StreamReader(await response.Content.ReadAsStreamAsync(), encoding))
                   {
                       string responseText = reader.ReadToEnd();
                       menulist = JsonConvert.DeserializeObject<List<RobotViewModel>>(responseText);
                   }
               }
           }
           catch (Exception ex)
           {
               throw ex;
           }
       }
       return menulist;
   }
   

   然后在异步委托(delegate)中使用它:

           navigationView.NavigationItemSelected += async delegate
           {
               AndHUD.Shared.Show(this, "Please Wait", -1, AndroidHUD.MaskType.Clear);
   
               var botList = new List<RobotViewModel>();
               var cts = new CancellationTokenSource();
   
               try
               {
                   _userRepo = await new Repository<User>().MakeDatabaseAsync();
                   var user = await _userRepo.Table.Where(p => p.LoggedIn).FirstOrDefaultAsync();
                   botList = await client.GetBot(user.AccessToken);
                   if (botList.Count > 0)
                   {
                       foreach (var item in botList)
                       {
                           var bot = await _botRepo.Table.Where(p => p.Token == item.Token).FirstOrDefaultAsync();
                           if (bot == null)
                               await _botRepo.CreateAsync(new Robot
                               {
                                   Name = item.Name,
                                   Token = item.Token,
                                   TokenUrl = item.TokenUrl,
                                   UserId = loggedInUser.Id,
                                   Description = item.Description
                               });
                           else
                           {
                               bot.Name = item.Name;
                               bot.Token = item.Token;
                               bot.TokenUrl = item.TokenUrl;
                               bot.UserId = loggedInUser.Id;
                               bot.Description = item.Description;
                               await _botRepo.UpdateAsync(bot);
                           }
                       }
                       SetData(botList, out myAdapter);
                       expandableListView.SetAdapter(myAdapter);
                       AndHUD.Shared.ShowSuccess(this, "Success", MaskType.Clear, TimeSpan.FromSeconds(2));
                   }
                   else
                   {
                       _userRepo = await new Repository<User>().MakeDatabaseAsync();
                       user = await _userRepo.Table.Where(p => p.LoggedIn).FirstOrDefaultAsync();
                       var loginResponse = await client.Login(user.UserName, user.Password);
                       botList = await client.GetBot(loginResponse.access_token);
                       if (botList.Count > 0)
                       {
                           foreach (var item in botList)
                           {
                               var bot = await _botRepo.Table.Where(p => p.Token == item.Token).FirstOrDefaultAsync();
                               if (bot == null)
                                   await _botRepo.CreateAsync(new Robot
                                   {
                                       Name = item.Name,
                                       Token = item.Token,
                                       TokenUrl = item.TokenUrl,
                                       UserId = loggedInUser.Id,
                                       Description = item.Description
                                   });
                               else
                               {
                                   bot.Name = item.Name;
                                   bot.Token = item.Token;
                                   bot.TokenUrl = item.TokenUrl;
                                   bot.UserId = loggedInUser.Id;
                                   bot.Description = item.Description;
                                   await _botRepo.UpdateAsync(bot);
                               }
                           }
                           SetData(botList, out myAdapter);
                           expandableListView.SetAdapter(myAdapter);
                           AndHUD.Shared.ShowSuccess(this, "Success", MaskType.Clear, TimeSpan.FromSeconds(2));
                       }
                   }
               }
               catch (Exception ex)
               {
                   if (ex is AggregateException)
                   {
                       AndHUD.Shared.ShowError(this, "IO Error", MaskType.Clear, TimeSpan.FromSeconds(2));
                   }
                   else
                       AndHUD.Shared.ShowError(this, "Unknown", MaskType.Clear, TimeSpan.FromSeconds(2));
               }
           };
   

   现在一切正常!感谢您的宝贵时间!