如何使用 Await 方法加载新页面

Question

这是我的登录方法：

    #region LoginMethod
    bool login = false;
    public async Task GetAccounts()
    {
        MainWin w = new MainWin();

        await Task.Run(() =>
        {
            this.Dispatcher.Invoke(() =>
            {
                using (SqlConnection connection = new SqlConnection(PublicVar.ConnectionString))
                {
                    gymEntities2 database = new gymEntities2();
                    SqlConnection con1 = new SqlConnection(PublicVar.ConnectionString);
                    PublicVar.TodayTime = String.Format("{0:yyyy/MM/dd}", Convert.ToDateTime(TimeNow.Text));
                    con1.Open();

                    SqlCommand Actives = new SqlCommand("Select DISTINCT (LockEndDate) from LockTable Where Username = '" + txt_username.Text + "' and Password = '" + txt_password.Password + "'", con1);
                    object Active = Actives.ExecuteScalar();
                    string SystemActive = Convert.ToString(Active);

                    //   SqlCommand Commandcmds = new SqlCommand("update VW_TimeOut set UserActive = 2 where UserEndDate < '" + String.Format("{0:yyyy/MM/dd}", Convert.ToDateTime(TimeNow.Text)) + "'", con1);
                    //   Commandcmds.ExecuteScalar();

                    SqlCommand Commandcmd = new SqlCommand("SELECT COUNT(*) FROM LockTable Where Username = '" + txt_username.Text + "' and Password = '" + txt_password.Password + "' and LockEndDate between '" + String.Format("{0:yyyy/MM/dd}", Convert.ToDateTime(Lock.Text)) + "' And '" + SystemActive + "'", con1);
                    int userCount = (int)Commandcmd.ExecuteScalar();

                    //Find Gym ID -> To Set Public Value Strings
                    SqlCommand FindGymID = new SqlCommand("Select DISTINCT (LockID) from LockTable Where Username = '" + txt_username.Text + "' and Password = '" + txt_password.Password + "'", con1);
                    object ObGymID = FindGymID.ExecuteScalar();

                    if (userCount > 0)
                    {
                        try
                        {
                            RegistryKey UsernameKey = Registry.CurrentUser.CreateSubKey("SOFTWARE\\GYM");

                            if (CheakRem.IsChecked == true)
                                if ((string)UsernameKey.GetValue("UserNameRegister") != "")
                                {
                                    UsernameKey.SetValue("UserNameRegister", txt_username.Text.Trim());
                                    UsernameKey.SetValue("PasswordRegister", Module.Decode.EncryptTextUsingUTF8(txt_password.Password.Trim()));
                                }

                            PublicVar.GymID = Convert.ToString(ObGymID);
                            login = true;
                        }
                        catch
                        {

                            w.Username = null;
                            w.Password = null;
                        }
                    }
                    else
                    {
                        ErrorPage pageerror = new ErrorPage();

                        con1.Close();
                        w.Username = null;
                        w.Password = null;
                    }
                    con1.Close();
                }
            });
        });

        if (login == true)
        {
            w.Username = txt_username.Text;
            w.Password = txt_password.Password;
            w.Show();
            this.Close();
        }
    }
    #endregion

但它不起作用 - 每当我按下按钮时，我的表单都会挂起。

private async void btn_join_Click(object sender, RoutedEventArgs e)
{
    await GetAccounts();
}

当我按下异步按钮时，它不起作用，我的程序被挂起。 我的方法的哪一部分是错误的？ 我真正想要的是打开一个新页面的按钮， 但我不希望它延迟打开...有人告诉我使用 await 方法，但它仍然延迟打开。

Answer 1

以上两个答案都是正确的。但也许修复你的代码会让事情变得更清楚。您应该按照上面的建议和如下所示将 UI 与任务分开。希望我没有语法错误，因为我只是在没有 IDE 的情况下对其进行了修改。基本上，我将 GetAccounts 更改为仅处理数据库并让 PopulateMethodAsync 处理 UI。这意味着 GetAccounts 将在后台运行，完成后会将结果提供给 UI 部分 (PopulateMethodAsync)。

    #region LoginMethod
    bool login = false;
    public async Task PopulateMethodAsync()
    {
        var isLoginSuccess = await GetAccounts(txt_username.Text.Trim(), txt_password.password.Text.Trim(), Lock.Text.Trim(), TimeNow.Text.Trim());

        MainWin w = new MainWin();

        if (login == true)
        {
            w.Username = txt_username.Text;
            w.Password = txt_password.Password;
            w.Show();
            this.Close();
        }
        else
        {
            w.Username = null;
            w.Password = null;
        }
    }

    public async Task<bool> GetAccounts(string txt_username, string txt_password, string Lock, string TimeNow)
    {
        await Task.Run(() =>
        {
            using (SqlConnection connection = new SqlConnection(PublicVar.ConnectionString))
            {
                gymEntities2 database = new gymEntities2();
                SqlConnection con1 = new SqlConnection(PublicVar.ConnectionString);
                PublicVar.TodayTime = String.Format("{0:yyyy/MM/dd}", Convert.ToDateTime(TimeNow));
                con1.Open();

                SqlCommand Actives = new SqlCommand("Select DISTINCT (LockEndDate) from LockTable Where Username = '" + txt_username + "' and Password = '" + txt_password + "'", con1);
                object Active = Actives.ExecuteScalar();
                string SystemActive = Convert.ToString(Active);

                //   SqlCommand Commandcmds = new SqlCommand("update VW_TimeOut set UserActive = 2 where UserEndDate < '" + String.Format("{0:yyyy/MM/dd}", Convert.ToDateTime(TimeNow.Text)) + "'", con1);
                //   Commandcmds.ExecuteScalar();

                SqlCommand Commandcmd = new SqlCommand("SELECT COUNT(*) FROM LockTable Where Username = '" + txt_username + "' and Password = '" + txt_password + "' and LockEndDate between '" + String.Format("{0:yyyy/MM/dd}", Convert.ToDateTime(Lock)) + "' And '" + SystemActive + "'", con1);
                int userCount = (int)Commandcmd.ExecuteScalar();

                //Find Gym ID -> To Set Public Value Strings
                SqlCommand FindGymID = new SqlCommand("Select DISTINCT (LockID) from LockTable Where Username = '" + txt_username + "' and Password = '" + txt_password + "'", con1);
                object ObGymID = FindGymID.ExecuteScalar();

                if (userCount > 0)
                {
                    try
                    {
                        RegistryKey UsernameKey = Registry.CurrentUser.CreateSubKey("SOFTWARE\\GYM");

                        if (CheakRem.IsChecked == true)
                            if ((string)UsernameKey.GetValue("UserNameRegister") != "")
                            {
                                UsernameKey.SetValue("UserNameRegister", txt_username);
                                UsernameKey.SetValue("PasswordRegister", Module.Decode.EncryptTextUsingUTF8(txt_password));
                            }

                        PublicVar.GymID = Convert.ToString(ObGymID);

                        con1.Close();

                        return true;
                    }
                    catch
                    {

                    }
                }

                con1.Close();
            }
        });

        return false;
    }
    #endregion

    private async void btn_join_Click(object sender, RoutedEventArgs e)
    {
        await PopulateMethodAsync();
    }

希望这能回答你的问题

Answer 2

您在任务方法中使用 Dispatcher.Invoke() 挂起程序。

Dispatcher.Invoke() 使代码在 WPF 的 UI 线程上同步执行，并且在此代码完成之前不会返回。同时，在您的“异步按钮”中，代码​​等待任务完成，这就是您的死锁。

您不需要 Task.Run 与 Dispatcher.Invoke。

你应该这样做：

1. 创建并显示您的表单。
2. await Task.Run - 从数据库中获取数据，但不要在 UI 中推送任何内容。您可以将值返回到一个简单的类中 并用于创建类型化任务。
3. 使用从数据库返回的值填充 UI。

如果你显示更多代码，我可以更精确。

Answer 3

看看这行this.Dispatcher.Invoke(() =>

Dispatcher.Invoke 是一个同步调用，它会阻止你的线程运行直到它完成。直到回调返回后，控件才会返回到调用对象，因此导致 GUI 无响应。

您可能希望使用异步操作Dispatcher.BeginInvoke 而不是Dispatcher.Invoke (example)。或使用Dispatcher.Invoke仅当您确实需要修改或更新 UI 内容。例如，

Dispatcher.Invoke(() =>
{
    w.Username = null;
    w.Password = null;
});