我如何将用户从视图模型导航到另一个页面

Question

我如何在获得访问令牌和用户成功登录后将用户导航到仪表板页面，或者当用户输入错误的用户名或密码时出现错误消息

这是我的登录视图模型

using RoyalSales.Views;
using System.Windows.Input;
using Xamarin.Forms;
using RoyalSalesAPI.Services;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Android.App;
using Android.Content.Res;
using RoyalSales.Helpers;

namespace RoyalSales.ViewModels
{
    class LoginViewModel
    {
        private APIServices _APIServices = new APIServices();

        public string Username { get; set; }
        public string Password { get; set; }
        public String Message { get; set; }
        public ICommand Logincommand => new Command(async () =>
{
var accesssToken = await _APIServices.LoginAsync(Username, Password);
if (!string.IsNullOrEmpty(accesssToken))
{
Message = "login succeed";

Settings.Username = Username;

Settings.Password = Password;

Settings.AccessToken = accesssToken;
// here i want navigate user to dashboard page 
}
else
{
Message = "wrong username or password";
// here i want show message dialoge to tell user theres an wrong username or 
password 

                                                          }
                                                      });
        public ICommand LogOutcommand
        {
            get
            {
                return new Command( () =>
                {


                        Settings.AccessToken = null;

                });
            }
        }



        public LoginViewModel()
        {
            if (!string.IsNullOrEmpty(Settings.Username))
            {
                Username = Settings.Username;
                Password = Settings.Password;
            }
        }
    }
}

这是我的 loginpage.cs

using Javax.Security.Auth;
using RoyalSales.Views;
using Android.Provider;
using RoyalSalesAPI.Services;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

using Xamarin.Forms;
using Xamarin.Forms.Xaml;
using RoyalSales.ViewModels;
using RoyalSales.Helpers;
using Settings = RoyalSales.Helpers.Settings;

namespace RoyalSales
{
    [XamlCompilation(XamlCompilationOptions.Compile)]
    public partial class Login : ContentPage
    {
        public APIServices aPIServices = new APIServices();
        private string accessToken = Settings.AccessToken.ToString();
        public Login()
        {
            InitializeComponent();
            NavigationPage.SetHasNavigationBar(this, false);


        }

        private async void Button_Clicked(object sender, EventArgs e)
        {



        }
    }
}

这是我的 loginpage.xaml

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage
    x:Class="RoyalSales.Login"
    xmlns="http://xamarin.com/schemas/2014/forms"
    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
    xmlns:viewModels="clr-namespace:RoyalSales.ViewModels;assembly=RoyalSales"
    Title="login page"
    BackgroundColor="#F38906">
    <ContentPage.BindingContext>
        <viewModels:LoginViewModel />
    </ContentPage.BindingContext>
    <ContentPage.Content>
        <StackLayout
            Padding="20"
            Orientation="Vertical"
            Spacing="30">
            <BoxView HeightRequest="20" />
            <Image
                HorizontalOptions="Center"
                Source="almotaheda.png"
                WidthRequest="175" />
            <Label
                FontSize="Large"
                HorizontalOptions="Center"
                Text="slogn"
                TextColor="White" />
            <Frame BackgroundColor="#FBD7AC" HasShadow="False">
                <StackLayout Orientation="Vertical" Spacing="10">
                    <Entry
                        x:Name="UserNameEntry"
                        HeightRequest="40"
                        HorizontalTextAlignment="Center"
                        Placeholder="username"
                        PlaceholderColor="#F38906"
                        Text="{Binding Username}"
                        TextColor="Black" />
                    <Entry
                        x:Name="PasswordEntry"
                        HeightRequest="40"
                        HorizontalTextAlignment="Center"
                        IsPassword="True"
                        Placeholder="Password"
                        PlaceholderColor="#F38906"
                        Text="{Binding Password}"
                        TextColor="Black" />

                </StackLayout>
            </Frame>
            <Label
                FontSize="20"
                Text="{Binding Message}"
                TextColor="#FFFFFF" />
            <Button
                BackgroundColor="White"
                Command="{Binding Logincommand}"
                FontAttributes="Bold"
                FontSize="20"
                HorizontalOptions="FillAndExpand"
                Text="login"
                TextColor="#F38906" 
                Clicked="Button_Clicked"/>
            <BoxView HeightRequest="20" />

        </StackLayout>

    </ContentPage.Content>
</ContentPage>

如果用户名或密码错误，请帮助我将用户导航到仪表板页面或错误消息

Answer 1

您可以在设置AccessToken

后使用PushAsync或PushModalAsync

例如：

await App.Current.MainPage.Navigation.PushAsync(new dashboardPage(), true);

为了显示来自视图模型的警报，您可以使用：

await Application.Current.MainPage.DisplayAlert("Error", "Login message here", "Dismiss");

我如何将用户从视图模型导航到另一个页面

how i can navigate user to another page from viewmodel

authentication

mvvm

asp.net-authorization

asp.net-web-api

xamarin.forms