如何关闭 Xamarin 表单中的当前窗口？

Question

我有一个 Xamarin Forms PCL 项目，它由几个选项卡式页面组成。当应用程序启动时，它会检查用户是否已登录。如果未登录，则加载登录屏幕，否则加载 MainPage（创建选项卡式项目）。

我遇到的问题是，在登录屏幕上，我只想在他们成功登录后关闭此窗口，但是通过使用 PopModalAsync，页面无法获取自身的实例（导致空异常） .然后该页面就坐在那里什么也不做，直到您重新启动它并让您进入。

我需要一种关闭登录屏幕的方法，但似乎找不到关于如何做到这一点的明确建议。

App.cs：

private async void Login_Clicked(object sender, EventArgs e)
{
    if ((!string.IsNullOrWhiteSpace(username.Text) && !string.IsNullOrWhiteSpace(password.Text)))
    {
        indicator.IsVisible = true;
        indicator.IsRunning = true;
        LoggedInUserInfoRoot liuir = await WebDataAccess.LoginUser(username.Text, password.Text);

        try
        {
            if (liuir.user != null)
            {
                if (liuir.user.userId > 0)
                {
                    UserInfoRepository.UpdateUserInformation(liuir.user.userId, DateTime.Now, liuir.user.userName);
                    await WebDataAccess.SaveSwipesToCloud();
                    await Navigation.PushModalAsync(new MainPage());
                    //var poppedPage = await Navigation.PopModalAsync();
                }
                else
                {
                    DisplayAlert("Login", "Your username or password is incorrect", "Ok");
                    indicator.IsVisible = false;
                    indicator.IsRunning = false;
                }
            }
            else
            {
                DisplayAlert("Login", "Your username or password is incorrect", "Ok");
                indicator.IsVisible = false;
                indicator.IsRunning = false;
            }

        }
        catch (Exception ex)
        {
            ErrorRepository.InsertError(ex.ToString());
        }
    }
    else
    {
        DisplayAlert("Login", "You must enter both a username and password", "Ok");
        indicator.IsVisible = false;
        indicator.IsRunning = false;
    }
}

登录界面：

private async void Login_Clicked(object sender, EventArgs e)
{
    if ((!string.IsNullOrWhiteSpace(username.Text) && !string.IsNullOrWhiteSpace(password.Text)))
    {
        indicator.IsVisible = true;
        indicator.IsRunning = true;
        LoggedInUserInfoRoot liuir = await WebDataAccess.LoginUser(username.Text, password.Text);

        try
        {
            if (liuir.user != null)
            {
                if (liuir.user.userId > 0)
                {
                    UserInfoRepository.UpdateUserInformation(liuir.user.userId, DateTime.Now, liuir.user.userName);
                    await WebDataAccess.SaveSwipesToCloud();
                    var poppedPage = await Navigation.PopModalAsync();
                }
                else
                {
                    DisplayAlert("Login", "Your username or password is incorrect", "Ok");
                    indicator.IsVisible = false;
                    indicator.IsRunning = false;
                }
            }
            else
            {
                DisplayAlert("Login", "Your username or password is incorrect", "Ok");
                indicator.IsVisible = false;
                indicator.IsRunning = false;
            }

        }
        catch (Exception ex)
        {
            ErrorRepository.InsertError(ex.ToString());
        }
    }
    else
    {
        DisplayAlert("Login", "You must enter both a username and password", "Ok");
        indicator.IsVisible = false;
        indicator.IsRunning = false;
    }
}

主页：

public MainPage()
{
    Children.Add(new Clocking());
    Children.Add(new ChangePassword{ BackgroundColor = Color.FromHex("59a092") });
    Children.Add(new CompanySetup { BackgroundColor = Color.FromHex("59a092") });
    Children.Add(new Log { BackgroundColor = Color.FromHex("59a092") });
    isuserloggedin();
}

public async void isuserloggedin()
{
    bool isuserloggedin = false;
    if (UserInfoRepository.UserLoggedInTime() != null)
    {
        if (UserInfoRepository.UserLoggedInTime() < DateTime.Now.AddMinutes(-60))
        {
            isuserloggedin = false;
        }
        else
        {
            isuserloggedin = true;
        }
    }
    if (isuserloggedin == false)
    {
        //  MainPage = new Login { BackgroundColor = Color.FromHex("59a092") };
        await Navigation.PushModalAsync(new Login());
    }

}

Answer 1

我的标签页

public class MyTabbedPage:TabbedPage

别忘了用这个推送你的页面

await Navigation.PushModalAsync(new NavigationPage(new MyTabbedPage()));

我有比你的代码更多的是这个

BackgroundColor = Color.FromRgb (76, 108, 139)
Device.OnPlatform(() => 
{
    this.Padding = new Thickness(0, 30, 0, 0);
});

and i add my pages with this function
void AddPage(string title, params View[] views) 
    {
        var content = new StackLayout();
        foreach (var view in views)
            content.Children.Add(view);
        this.Children.Add(new ContentPage 
        {
            Content = content,
            Title = title
        });
    }

希望对你有帮助