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This article mainly discusses the failure of using Prism area navigation in WPF. This problem and corresponding solutions have been discussed many times in other blogs,
For example, override the OnInitialized method, and so on. I don't think this is the root of the problem. In that case, let's analyze the specific process of Prism's IRegionManager in the future.

Prism initialization process

First, let's analyze the following code to create the home page of the application

       protected override Window CreateShell()
        {
            return Container.Resolve<MainWindow>();
        }

In this MainWindow, if we set the following area, we can use IRegionManager to navigate, as shown below:

<ContentControl Grid.Row="1" prism:RegionManager.RegionName="ShowRegion" />

Now the problem comes. Once we destroy the instance of this window and re create a MainWindow, you will find that you can't navigate. This is the problem we understand. Is the Region invalid?
No, to solve this problem, we need to know what the Prism framework does. After checking the source code, we find the following initialization code:

           var shell = CreateShell();  
            if (shell != null)
            {
                MvvmHelpers.AutowireViewModel(shell);
                RegionManager.SetRegionManager(shell, _containerExtension.Resolve<IRegionManager>());
                RegionManager.UpdateRegions();
                InitializeShell(shell);
            }

We learned that after getting the MainWindow from the beginning, we successively bound the context, set the IRegionManager instance and update the region.

Here, we know at least a few things.

• Timing of DataContext initialization of MainWindow
• Initialization process of IRegionManager in MainWindow window
• Area refresh action

After completing these actions, ShowDialog finally shows the home page, so we can happily use IRegionManager to navigate here.

Analysis results

If you want to navigate in a window, in addition to defining the area, you also need to set the IRegionManager instance and refresh area for the window. The core is these two lines of code:

 RegionManager.SetRegionManager(shell, _containerExtension.Resolve<IRegionManager>());
 RegionManager.UpdateRegions();

Now that we know this, another problem is solved naturally. The problem that the pop-up service cannot navigate in Prism is not implemented in the IDialogService provided by Prism framework
Setting IRegionManager and refreshing area is the root of the problem, so we must manually modify the implementation to support navigation.

Navigation in pop-up window

Example: the following code shows how to set the area and refresh the area in the pop-up window.

            var provider = ContainerLocator.Container.Resolve<IContainerProvider>();
            var regionManager = ContainerLocator.Container.Resolve<IRegionManager>();
            var win = provider.Resolve<object>("ShowWindow");
            if (win is Window view)
            {
                RegionManager.SetRegionManager(view, regionManager);
                RegionManager.UpdateRegions();

                view.ShowDialog();
            }

Of course, you can implement the IDialogService interface by yourself, covering the internal implementation provided by Prism, so as to achieve the behavior of pop-up window supporting navigation, for example:

   public interface IMyDialogService : IDialogService
    {

    }

    public class MyDialogService : DialogService, IMyDialogService
    {
        public MyDialogService(IContainerExtension containerExtension)
            : base(containerExtension)
        {
        }

        public new void ShowDialog(string name, IDialogParameters parameters, Action<IDialogResult> callback)
        {
            //...
        }
    }

summary

For any window, we can use IRegionManager to navigate. When the framework is initialized for the first time, Prism only helps us deal with the regional settings and refresh behavior.
If we want to use area navigation in other places, we need to manually set the area and refresh the area.