在不同的类中实现INotifyPropertyChanged

Question

I have 2 ViewModels in my application. The first (FirstPageViewModel) is responsible for the data which gets shown in the TextBoxes in my View. The other ViewModel (NavigationViewModel) is responsible for the Navigation between my pages AND to change the values of the TextBlocks:

<StackPanel>
<Button Content="SecondPage" 
        DataContext="{Binding Source={StaticResource NavigationVM}}" /// reference to App.xaml
        Command="{Binding NavigationCommand}" 
        CommandParameter="SecondPage" />
<Grid  DataContext="{Binding Source={StaticResource FirstPageViewModel}}">
  <TextBlock  Text="{Binding helloWorld.Counter, UpdateSourceTrigger=PropertyChanged}"/>
  <TextBlock  Text="{Binding helloWorld.Message, UpdateSourceTrigger=PropertyChanged}"/>
    ...
</Grid>

Now the Navigation works fine. But if I try to change the values in the TextBlocks by using the NavigationCommand (=Button Click) in "NavigationViewModel", nothing changes: (TextBlockSetter implements INotifyPropertychanged)

public TextBlockSetter _helloWorld;


    public NavigationViewModel()
    {

        _helloWorld = new TextBlockSetter();

    }

    public TextBlockSetter helloWorld
    {
        get
        {
            return _helloWorld;
        }
        set
        {
            _helloWorld = value;
        }
    }
 private void navigationCommand(object destination)
{
  switch (destination.ToString())
  {
    case "SecondPage":
      {

         ... ///Code for page Navigation

        helloWorld.Counter++;
        helloWorld.Message = "done";
        break;
      }
  }
}

"FirstPageViewModel" contains the same implementation and sets the values of the TextBoxes:

static int _roundCounter = 1;
public TextBlockSetter _helloWorld;

    public FirstPageViewModel()
    {
        helloWorld.Counter = _roundCounter;
        _helloWorld = new TextBlockSetter();

    }

    public TextBlockSetter helloWorld
    {
        get
        {
            return _helloWorld;
        }
        set
        {
            _helloWorld = value;
        }
    }

Has someone an idea how to properly implement those changes? My idea was to make a reference in NavigationViewModel to FirstPageViewModel, when the Textboxes should get changed. But unfortunately none of my ideas worked out well.

Answer 1

I dont fully understand but, what about use just a one viewmodel and define a screen property in that viewmodel.Therefore, you can set that property and then navigate in property changed event.

public static readonly DependencyProperty ScreenNameProperty =
        DependencyProperty.Register("ScreenName", typeof(String),
        typeof(ContentControl), new FrameworkPropertyMetadata("screen_1", new PropertyChangedCallback(ScreenNameChanged)));

    public String ScreenName
    {
        get { return (String)GetValue(ScreenNameProperty); }
        set { SetValue(ScreenNameProperty, value); }
    }

    private static void ScreenNameChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs eventArgs)
    {
        ContentControl originator = dependencyObject as ContentControl;
        if (originator != null)
        {
            // navigate here
        }
    }

bind ScreenName property to a property in your viewmodel.Then change propertt in viewmodel how you want.