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

Question

我在Xamarin.Forms.ContentPage有线到按钮点击事件中有以下方法

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());
        }
    }
}

在下面的代码行中Navigation.PushAsync(new HomePage());,我在调试时遇到以下异常:

Android上不支持全局支持PushAsync,请使用NavigationPage

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

Answer 1

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());
    }
}

但是你没有启动NavigationPage,它通常在App.cs类中完成,或者至少应该在调用"PushAsync"之前启动它:

MainPage = new NavigationPage(new PageA());

Answer 2

在app.xaml.cs文件中,

更换

 MainPage = new <namespace>.MainPage();

同

 MainPage = new NavigationPage(new <namespace>.MainPage());

然后使用

 await Navigation.PushAsync(new NavigationPage(new MainPage2()));

Answer 3

您需要将LoginPage包含在NavigationPage中.这将修复您的错误,但会让您在导航堆栈中包含LoginPage.

另一种方法是将HomePage作为应用程序的根目录,然后在其上以模态方式显示LoginPage.只有当用户成功登录时才会关闭LoginPage模式,以便他们可以看到HomePage.

Answer 4

首先在“主应用程序页面”中进行设置，然后在“内容页面”中进行设置以转到其他页面：

Answer 5

我只用pushModalAsync更改pushAsync ：）

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());
           Navigation.PushModalAsync(new HomePage());
    }
}

Answer 6

检查您在之前的导航中是否使用了 NavigationPage：

错误：Application.Current.MainPage = new LoginPage();

正确的：Application.Current.MainPage = new NavigationPage(new LoginPage());