Prism loading dependent views

Description

When a view is injected into a region, trigger the load of other views in other regions and pass them the same DataContext.

Region behavior and Attribute

Add a region behavior which create the dependent views and inject them into the target region.

DependentViewAttribute.cs

[AttributeUsage(AttributeTargets.Class, AllowMultiple = true)] public class DependentViewAttribute : Attribute { public Type Type { get; } public string TargetRegionName { get; } public DependentViewAttribute(Type viewType, string targetRegionName) { Type = viewType; TargetRegionName = targetRegionName; } }

DependentViewRegionBehavior.cs

public class DependentViewRegionBehavior : RegionBehavior { private readonly Dictionary<object, List<DependentViewInfo>> _dependentViewCache = new Dictionary<object, List<DependentViewInfo>>(); protected override void OnAttach() { Region.ActiveViews.CollectionChanged += ActiveViewsOnCollectionChanged; } private void ActiveViewsOnCollectionChanged(object sender, NotifyCollectionChangedEventArgs e) { if (e.Action == NotifyCollectionChangedAction.Add) { foreach (var view in e.NewItems) { if (!_dependentViewCache.TryGetValue(view, out var viewInfoList)) { viewInfoList = new List<DependentViewInfo>(); foreach (var attribute in GetCustomAttribute<DependentViewAttribute>(view.GetType())) { var viewInfo = CreateDependentView(attribute); if (viewInfo.View is FrameworkElement viewToInject && view is FrameworkElement viewTrigger) { viewToInject.DataContext = viewTrigger.DataContext; } viewInfoList.Add(viewInfo); } if (!_dependentViewCache.ContainsKey(view)) { _dependentViewCache.Add(view, viewInfoList); } } viewInfoList.ForEach(x => Region.RegionManager.Regions[x.TargetRegionName].Add(x.View)); } } if (e.Action == NotifyCollectionChangedAction.Remove) { foreach (var view in e.OldItems) { if (_dependentViewCache.TryGetValue(view, out var viewInfoList)) { viewInfoList.ForEach(x => Region.RegionManager.Regions[x.TargetRegionName].Remove(x.View)); } } } } private DependentViewInfo CreateDependentView(DependentViewAttribute attribute) { return new DependentViewInfo { View = attribute.Type != null ? Activator.CreateInstance(attribute.Type) : null, TargetRegionName = attribute.TargetRegionName }; } private static IEnumerable<T> GetCustomAttribute<T>(Type type) => type.GetCustomAttributes(typeof(T), true).OfType<T>(); } internal class DependentViewInfo { public object View { get; set; } public string TargetRegionName { get; set; } }

App.xaml.cs

protected override void ConfigureDefaultRegionBehaviors(IRegionBehaviorFactory regionBehaviors) { base.ConfigureDefaultRegionBehaviors(regionBehaviors); regionBehaviors.AddIfMissing(nameof(DependentViewRegionBehavior), typeof(DependentViewRegionBehavior)); }

Views and ViewModels

MainWindow.xaml

<Grid> <Grid.RowDefinitions> <RowDefinition Height="Auto" /> <RowDefinition Height="*" /> </Grid.RowDefinitions> <Menu prism:RegionManager.RegionName="MenuRegion" /> <ContentControl Grid.Row="1" prism:RegionManager.RegionName="StepRegion" /> </Grid>

StepOneView.xaml.cs

[DependentView(typeof(NextMenuItemView), "MenuRegion")] public partial class StepOneView { }

StepOneViewModel.cs

public class StepOneViewModel : BindableBase { private readonly IRegionManager _regionManager; public ICommand GoToNextStepCommand { get; } public StepOneViewModel(IRegionManager regionManager) { _regionManager = regionManager; GoToNextStepCommand = new DelegateCommand(GoToNextStep); } private void GoToNextStep() { _regionManager.RequestNavigate("StepRegion", "StepTwoView"); } }

StepTwoView.xaml.cs

[DependentView(typeof(PreviousMenuItemView), "MenuRegion")] [DependentView(typeof(NextMenuItemView), "MenuRegion")] public partial class StepTwoView { }

StepTwoViewModel.cs

public class StepTwoViewModel : BindableBase { private readonly IRegionManager _regionManager; public ICommand GoToPreviousStepCommand { get; } public ICommand GoToNextStepCommand { get; } public StepTwoViewModel(IRegionManager regionManager) { _regionManager = regionManager; GoToPreviousStepCommand = new DelegateCommand(GoToPreviousStep); GoToNextStepCommand = new DelegateCommand(GoToNextStep); } private void GoToPreviousStep() { _regionManager.RequestNavigate("StepRegion", "StepOneView"); } private void GoToNextStep() { _regionManager.RequestNavigate("StepRegion", "StepThreeView"); } }

StepThreeView.xaml.cs

[DependentView(typeof(PreviousMenuItemView), "MenuRegion")] public partial class StepThreeView { }

StepThreeViewModel.cs

public class StepThreeViewModel : BindableBase { private readonly IRegionManager _regionManager; public ICommand GoToPreviousStepCommand { get; } public StepThreeViewModel(IRegionManager regionManager) { _regionManager = regionManager; GoToPreviousStepCommand = new DelegateCommand(GoToPreviousStep); } private void GoToPreviousStep() { _regionManager.RequestNavigate("StepRegion", "StepTwoView"); } }