如何使用 c# 在 xamarin.forms 登录成功后更改内容

Question

I have a page flyview and a login login.I want if I login successfully, it will change label in my username.

mainpage.xaml :

 <Shell.FlyoutHeader>
        <local:HeaderContentView></local:HeaderContentView>
    </Shell.FlyoutHeader>

HeaderContentView.xaml :

 <Grid BackgroundColor="#326e52"
                  HeightRequest="200">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*"></ColumnDefinition>
            <ColumnDefinition Width="*"></ColumnDefinition>
        </Grid.ColumnDefinitions>

        <StackLayout Padding="10,0,10,20"
                             VerticalOptions="EndAndExpand" Orientation="Horizontal" Grid.Column="0">
            <Label Text="Đăng nhập"
                           TextColor="White"
                           FontAttributes="Bold"
                           HorizontalTextAlignment="Center"
                           VerticalTextAlignment="Center" >
                <Label.GestureRecognizers>
                    <TapGestureRecognizer Tapped="Link_dang_nhap"/>
                </Label.GestureRecognizers>
            </Label>
            <Label Text="Đăng ký"
                           TextColor="White"
                           FontAttributes="Bold"
                           HorizontalTextAlignment="Center"
                           VerticalTextAlignment="Center" >
                <Label.GestureRecognizers>
                    <TapGestureRecognizer Tapped="Link_dang_ky"/>
                </Label.GestureRecognizers>
            </Label>
        </StackLayout>
    </Grid>

I want if I login successfully it will change label text="Đăng nhập" and "Đăng ký" to my username

Answer 1

You can create a View Model and bind the AppShell to change the label text to your username. When logining, publish a message by MessagingCenter and change the label text. You could also set a static member or use a static Properties dictionary to save the login status.

App.cs:

  public partial class App : Application
     {
         public static Boolean IsLogin { set; get; } = false; // set a static member
         public App()
         {
             ......
          //   Application.Current.Properties["IsLogin"] = false; // use static Properties dictionary
            ......
         }
 }

Xaml:

<Shell.BindingContext>
         <vm:ShellViewModel></vm:ShellViewModel>
  </Shell.BindingContext>

The username binding with Label:

 <Label Text="{Binding UserName}"
                           TextColor="White"
                           FontAttributes="Bold"
                           HorizontalTextAlignment="Center"
                           VerticalTextAlignment="Center" >
                <Label.GestureRecognizers>
                    <TapGestureRecognizer Tapped="Link_dang_nhap"/>
                </Label.GestureRecognizers>
 </Label>

ViewModel:

 public class ShellViewModel: BaseViewModel// the BaseViewMode calls INotifyPropertyChanged method
{
      string _username = string.Empty;
      public string UserName
      {
             get { return _username ; }
             set { SetProperty(ref _username, value); }
      }
}

Push message when logging in successfully:

 private async void OnLoginClicked(object obj)
{
             ......
        MessagingCenter.Send<Object, string>(this, "UserName", "Setusername");// You could set the user name
        App.IsLogin = true;
        //   Application.Current.Properties["IsLogin"] = true;
         }

Subscribe this message in the constructor of ShellViewModel :

  public ShellViewModel()
  {
             MessagingCenter.Subscribe<Object, string>(this, "UserName", (sender, s) =>
             {
                 this.UserName = s;
             });
         UserName= App.IsLogin ? "Đăng nhập" : "testname";// test 
  }

Please pay attention to unsubscribing the message: https://docs.microsoft.com/en-us/xamarin/xamarin.forms/app-fundamentals/messaging-center#unsubscribe-from-a-message