Prism 4 - locally scoped RegionManager

Question

I have silverlight 4 application with PRISM 4, I'm using MEF.

My Shell defines one main region in which modules are loaded, I want modules to have their own RegionManager, so regions that they define are places in local RegionManager instead of global. And I want this local RegionManager to be resolved by container (for type IRegionManager) when inside the module.

However the method from documentation:

IRegion detailsRegion = this.regionManager.Regions["DetailsRegion"];
View view = new View();
bool createRegionManagerScope = true;
IRegionManager detailsRegionManager = detailsRegion.Add(view, null, 
                            createRegionManagerScope);

Doesnt work for me, when resolving IRegionManager from inside child view I still get GlobalRegionManager.

Lukazoid Lukazoid · Accepted Answer · 2012-02-10T12:10:55

I was in the same situation as you, I had a nested region manager, but all of the child views were still getting the global region manager. I came up with what I consider a reasonable solution.

First I define an interface:

/// <summary>
/// An interface which is aware of the current region manager.
/// </summary>
public interface IRegionManagerAware
{
    /// <summary>
    /// Gets or sets the current region manager.
    /// </summary>
    /// <value>
    /// The current region manager.
    /// </value>
    IRegionManager RegionManager { get; set; }
}

Then I setup a RegionBehavior like so:

/// <summary>
/// A behaviour class which attaches the current scoped <see cref="IRegionManager"/> to views and their data contexts.
/// </summary>
public class RegionAwareBehaviour : RegionBehavior
{
    /// <summary>
    /// The key to identify this behaviour.
    /// </summary>
    public const string RegionAwareBehaviourKey = "RegionAwareBehaviour";

    /// <summary>
    /// Override this method to perform the logic after the behaviour has been attached.
    /// </summary>
    protected override void OnAttach()
    {
        Region.Views.CollectionChanged += RegionViewsChanged;
    }

    private void RegionViewsChanged(object sender, NotifyCollectionChangedEventArgs e)
    {
        Contract.Requires<ArgumentNullException>(e != null);

        if (e.NewItems != null)
            foreach (var item in e.NewItems)
                MakeViewAware(item);
    }

    private void MakeViewAware(object view)
    {
        Contract.Requires<ArgumentNullException>(view != null);

        var frameworkElement = view as FrameworkElement;
        if (frameworkElement != null)
            MakeDataContextAware(frameworkElement);

        MakeAware(view);
    }

    private void MakeDataContextAware(FrameworkElement frameworkElement)
    {
        Contract.Requires<ArgumentNullException>(frameworkElement != null);

        if (frameworkElement.DataContext != null)
            MakeAware(frameworkElement.DataContext);
    }

    private void MakeAware(object target)
    {
        Contract.Requires<ArgumentNullException>(target != null);

        var scope = target as IRegionManagerAware;
        if (scope != null)
            scope.RegionManager = Region.RegionManager;
    }
}

Then apply this to all regions in your bootstrapper:

protected override IRegionBehaviorFactory ConfigureDefaultRegionBehaviors()
{
    var behaviours = base.ConfigureDefaultRegionBehaviors();

    behaviours.AddIfMissing(RegionAwareBehaviour.RegionAwareBehaviourKey, typeof(RegionAwareBehaviour));

    return behaviours;
}

Then all you have to do is implement IRegionManagerAware on your view/viewmodel, probably like so:

public class MyView : IRegionManagerAware
{
    IRegionManager RegionManager { set; get; }
}

Then when this view is added to a region, the behaviour will correctly set the RegionManager property to the currently scoped region manager.

Prism 4 - locally scoped RegionManager

2 Answers