Android 上不支持 PushAsync，请使用 NavigationPage - Xamarin.Forms

问题描述

我在连接到按钮单击事件的 Xamarin.Forms.ContentPage 中有以下方法

I have the following method in an Xamarin.Forms.ContentPage wired to a button click event

public class LoginPage : ContentPage
{
    private Button _loginButton = null;
    private Entry _PasswordInput = null;
    private Entry _UsernameInput = null;

    public LoginPage()
    {
        _UsernameInput = new Entry { Placeholder = "Username" };
        _PasswordInput = new Entry { Placeholder = "Password", IsPassword = true };

        _loginButton = new Button
        {
            Text = "Login",
            BorderRadius = 5
        }

        _loginButton.Clicked += LogIn;

        Content = new StackLayout
        {
            VerticalOptions = LayoutOptions.Center,
            Children =
            {
                 _UsernameInput, _PasswordInput, _loginButton,
            },
            Spacing = 15
        };
    }

    public async void LogIn(object sender, EventArgs eventsArgs)
    {
        //do authenticate stuff here
        SSO.MyAuthentication client = new SSO.MyAuthentication();

        bool isAuthenticated = client.Authenticate(_UsernameInput.Text, _PasswordInput.Text);

        if(isAuthenticated)
        {
             //Push home page to top of navigation stack
             Navigation.PushAsync(new HomePage());
        }
    }
}

在以下代码行 Navigation.PushAsync(new HomePage()); 中，我在调试时遇到以下异常:

On the following line of code Navigation.PushAsync(new HomePage());, I am getting the following exception while debugging:

Android 不支持 PushAsync，请使用导航页面

如何使用 Xamarin.Forms.NavigationPage 对象解决此问题?

How do I resolve this issue using a Xamarin.Forms.NavigationPage object?

推荐答案

您正在调用 PushAsync":

public partial class MainPage : ContentPage
{
    public MainPage()
    {
        InitializeComponent();
    }

    private void btnCourseList_Clicked(object sender, EventArgs e)
    {
        Navigation.PushAsync(new PageB());
    }
}

但是您没有启动 NavigationPage，这通常是在 App.cs 类中完成的，或者至少应该在调用 "PushAsync" 之前启动:

but you did not start the NavigationPage, which normally is done in the App.cs class, or at least it should be started before any call to "PushAsync":

MainPage = new NavigationPage(new PageA());

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