调用 PostAsync 方法会使应用程序崩溃

Question

我正在尝试使用 post 方法将用户信息发送到服务器。当我调用异步任务时，它立即崩溃。

这是我在 LoginPage.cs 中的内容

 async void SignInProcedure(object sender, EventArgs e) //function called when pressing the signin button
        {

            User user = new User(Entry_Username.Text, Entry_Password.Text); //putting username and password entered by the user in the entry box
            if (user.CheckInformation())//checks if the boxes are empty
            {

                var result = await App.RestService.Login(user);//RestService class
                await App.Current.MainPage.DisplayAlert("Login", "Login Successful", "Oke");

在 RestService.cs 中

public async Task<Token> Login(User user)//this is where the problem is
        {

            var postData = new List<KeyValuePair<string, string>>();            
            postData.Add(new KeyValuePair<string, string>("grant_type", grant_type));
            postData.Add(new KeyValuePair<string, string>("username", user.Username));
            postData.Add(new KeyValuePair<string, string>("password", user.Password));
            var content = new FormUrlEncodedContent(postData);
            var response = await PostResponseLogin<Token>(Constants.LoginUrl, content);
            DateTime dt = new DateTime();
            dt = DateTime.Today;
            response.expire_date = dt.AddSeconds(response.expire_in);
            return response;

        }

        public async Task<T> PostResponseLogin<T>(string weburl, FormUrlEncodedContent content) where T : class
        {

            var response = await client.PostAsync(weburl,content);

            var jsonResult = response.Content.ReadAsStringAsync().Result;

            var responseObject = JsonConvert.DeserializeObject<T>(jsonResult);

            return responseObject;
        }

服务器应该收到用户数据，但它没有收到任何东西。 我似乎找不到任何错误消息。

Answer 1

使用 SignInProcedure 而不是使用 async void，使用 async Task 并添加 try catch 块并检查。

Answer 2

我稍微修改了我的代码

async Task SignInProcedure(object sender, EventArgs e) //function called when pressing the signin button
        {

            User user = new User(Entry_Username.Text, Entry_Password.Text); //putting username and password entered by the user in the entry box
            if (user.CheckInformation())//checks if the boxes are empty
            {
                try
                {
                    var result = await App.RestService.Login(user);//RestService class
                    await App.Current.MainPage.DisplayAlert("Login", "Login Successful", "Oke");
                    if (result.access_token != null)
                    {
                        App.UserDatabase.SaveUser(user);
                    }
                }
                catch (Exception ex)
                {

                    System.Diagnostics.Debug.WriteLine(ex);
                }

将 void 更改为 Task 时出现此错误：Position 12:54. Signature (return type) of EventHandler "SmartLockApp.Views.LoginPage.SignInProcedure" doesn't match the event type

而且，如果我不将 void 更改为 Task，我无法在控制台中找到错误