如何在一帧中的多个页面之间导航，在 WPF C#

Question

I have:

• MainWindow.xaml ( where I have the frame )
• LoginPage.xaml
• SignUpPage.xaml

Here is the frame in MainWindow.xaml:

  <Frame x:Name="MainPage"
               Content="{Binding ApplicationViewModel.CurentPage,
                                Source={x:Static viewMod:ViewModelLocator.Instanze},
                                Converter={local:ApplicationPageValueConverter}}"/>

ApplicationViewModel is the application state as a view model:

 public class ApplicationViewModel 
 {
    /// <summary>
    /// The current page of the application
    /// </summary>
    public ApplicationPage CurentPage { get; set; } = ApplicationPage.Login;
 }

ViewModelLocator locates view models from the IoC for use in binding in Xaml files

public class ViewModelLocator
{
   /// <summary>
   /// Singleton instance of the locator
   /// </summary>
   public static ViewModelLocator Instance { get; private set; } = new ViewModelLocator();

   /// <summary>
   /// The application view model
   /// </summary>
   public static ApplicationViewModel ApplicationViewModel => IoC.Get<ApplicationViewModel>();   
 }

In ApplicationPageValueConverter I have this, to convert the page:

public override object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
          
  switch ((ApplicationPage)value)
  {
      case ApplicationPage.Login:
           return new LoginPage(); 
                
      case ApplicationPage.SignUp:
           return new SignUpPage();

      default:
        Debugger.Break();
         return null;
   }
}

In the MainViewModel which is ViewModel for MainWindow.xaml.cs I have a button "SignUp", and when I click the button is going to execute ICommand whose is doing this:

public ICommand LoginCommand { get; set; }      
LoginCommand = new RelayCommand(() => Login());

private void Login()
{
  IoC.Get<ApplicationViewModel>().CurentPage = ApplicationPage.SignUp;
}

The value of ApplicationViewModel.CurentPage is changed to ApplicationPage.SignUp but it doesn't go to ApplicationPageValueConverter to convert/show the page.

Here is the IoC code where OnStartup I'm doing this:

base.OnStartup(e);

IoC.SetUp();
....

I can't get whay it doesn't show the page, what I'm doing wrong?

Answer 1

ApplicationViewModel should implement INotifyPropertyChanged and raise the PropertyChanged event whenever the CurrentPage property is set:

public class ApplicationViewModel : INotifyPropertyChanged
{
    private ApplicationPage _currentPage = ApplicationPage.Login;

    /// <summary>
    /// The current page of the application
    /// </summary>
    public ApplicationPage CurentPage
    {
        get { return _currentPage; }
        set { _currentPage = value; NotifyPropertyChanged(); }
    }

    public event PropertyChangedEventHandler PropertyChanged;
    private void NotifyPropertyChanged([System.Runtime.CompilerServices.CallerMemberName] string propertyName = "") =>
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}

This is required for the view to be notified of the change and the converter to get invoked again.