prism - IsNavigationTarget not invoked when using RequestNavigate

Question

I am trying to learn the Prism Navigation support. Presently, I have a prism Region and I want to load view to that region using RegionManager.RequestNavigate(). The navigation does occur, however the IsNavigationTarget() of INavigationAware is not invoked, even if the ViewModel of the Navigation Target view implements INavigationAware interface. Here is the code that I am using.

Shell:

<StackPanel Margin="10">
    <TextBlock Text="Main Window"/>
    <Button Content="RegionA" Command="{Binding NavigateToACommand}" />
    <ContentControl prism:RegionManager.RegionName="MainRegion"/>
</StackPanel>

ShellViewModel:

private void NavigateToA () {
    Uri uri = new Uri("RegionAView", UriKind.Relative);
    RegionManager.RequestNavigate("MainRegion", uri);
}

RegionAView:

<UserControl x:Class="NavigationExample.RegionAView"
    <Grid>
        <TextBlock Text="This is Region A"/>
    </Grid>
</UserControl>

RegionAViewModel

public class RegionAViewModel : INavigationAware{

    public RegionAViewModel() {
    }

    public bool IsNavigationTarget(NavigationContext navigationContext) {
        return false; //Not Invoked
    }

    public void OnNavigatedTo(NavigationContext navigationContext) {
        //Gets Invoked
    }
}

RegionAView.xaml.cs

[Export("RegionAView")]
public partial class RegionAView : UserControl {
    public RegionAView() {
        InitializeComponent();
    }
}

Why does the IsNavigationTarget() not getting invoked prior to completion of Navigation?

Answer 1

I think your problem is that you export your view as singleton. modify VM and V as follow:

[Export("RegionAView")] 
[PartCreationPolicy(CreationPolicy.NonShared)]
public partial class RegionAView : UserControl 
{     
public RegionAView() 
{         
InitializeComponent();     
} 
} 

Basically, IsNavigationTarget will be invoked when you have existing instances. But it will not work for newly created instance.