some improvements

samples/Sample.Avalonia/Views/DView.axaml

@@ -5,17 +5,17 @@
     xmlns:an="https://github.com/NeverMorewd/AsyncNavigation"
     xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
     xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
-	xmlns:vm="using:Sample.Common"
+    xmlns:vm="using:Sample.Common"
     d:DesignHeight="450"
     d:DesignWidth="800"
-    mc:Ignorable="d"
-	x:DataType="vm:DViewModel">
+    x:DataType="vm:DViewModel"
+    mc:Ignorable="d">
     <DockPanel LastChildFill="True">
         <StackPanel DockPanel.Dock="Left" Orientation="Vertical">
-			<StackPanel Spacing="4" Orientation="Horizontal">
-				<Button Classes="GoBack"/>
-				<Button Classes="GoForward"/>
-			</StackPanel>
+            <StackPanel Orientation="Horizontal" Spacing="4">
+                <Button Classes="GoBack" />
+                <Button Classes="GoForward" />
+            </StackPanel>
             <Button
                 Classes="Navigation"
                 Content="ToA"
@@ -24,7 +24,7 @@
                 Classes="Navigation"
                 Content="ToE"
                 Tag="EView" />
-			<Button
+            <Button
                 Classes="Navigation"
                 Content="ToE:Delay"
                 Tag="EView:Delay" />
@@ -36,17 +36,18 @@
                 Classes="Navigation"
                 Content="ToE:New;Delay"
                 Tag="EView:New;Delay" />
-			<Button
-			   Classes="NavigationAndForget"
-			   Content="ToA:Forget"
-			   Tag="AView" />
-			<Button
-			   Classes="NavigationAndForget"
-			   Content="ToA:Forget;New"
-			   Tag="AView:New" />
+            <Button
+                Classes="NavigationAndForget"
+                Content="ToA:Forget"
+                Tag="AView" />
+            <Button
+                Classes="NavigationAndForget"
+                Content="ToA:Forget;New"
+                Tag="AView:New" />
         </StackPanel>
         <ScrollViewer>
             <TabControl
+                Name="tab"
                 an:RegionManager.PreferCache="True"
                 an:RegionManager.RegionName="TabRegion"
                 TabStripPlacement="Top">
@@ -57,7 +58,12 @@
                             Orientation="Horizontal"
                             Spacing="4">
                             <TextBlock VerticalAlignment="Center" Text="{ReflectionBinding ViewName}" />
-                            <Button Margin="10" Content="x" />
+                            <Button
+                                Margin="10"
+                                Command="{ReflectionBinding DataContext.RequestUnloadViewCommand,
+                                                            ElementName=tab}"
+                                CommandParameter="{Binding}"
+                                Content="x" />
                         </StackPanel>
                     </DataTemplate>
                 </TabControl.ItemTemplate>

samples/Sample.Common/AViewModel.cs

@@ -21,7 +21,7 @@ public AViewModel(IRegionManager regionManager)
     [ReactiveCommand]
     private Task UnloadView(string param)
     {
-        return RequestUnloadAsync();
+        return RequestUnloadAsync(CancellationToken.None);
     }
 
     [ReactiveCommand]

samples/Sample.Common/BViewModel.cs

@@ -34,7 +34,7 @@ private Task AsyncNavigateAndForget(string param)
     [ReactiveCommand]
     private Task UnloadView(string param)
     {
-        return RequestUnloadAsync();
+        return RequestUnloadAsync(CancellationToken.None);
     }
     public override async Task OnNavigatedToAsync(NavigationContext context)
     {

samples/Sample.Common/CViewModel.cs

@@ -20,6 +20,6 @@ private async Task AsyncNavigate(string param)
     [ReactiveCommand]
     private Task UnloadView(string param)
     {
-        return RequestUnloadAsync();
+        return RequestUnloadAsync(CancellationToken.None);
     }
 }

samples/Sample.Common/DViewModel.cs

@@ -1,4 +1,5 @@
-using AsyncNavigation.Abstractions;
+using AsyncNavigation;
+using AsyncNavigation.Abstractions;
 using AsyncNavigation.Core;
 using ReactiveUI.SourceGenerators;
 namespace Sample.Common;
@@ -35,4 +36,15 @@ private async Task GoBack()
     {
         await _regionManager.GoBack("TabRegion");
     }
+    [ReactiveCommand]
+    private async Task RequestUnloadView(NavigationContext navigationContext)
+    {
+        if (navigationContext.TryResolveNavigationAware(out var aware))
+        {
+            if (aware is ViewModelBase viewModel)
+            {
+                await viewModel.RequestUnloadAsync(CancellationToken.None);
+            }
+        }
+    }
 }

samples/Sample.Common/EViewModel.cs

@@ -20,7 +20,7 @@ public ObservableCollection<byte> HeavyItems
     [ReactiveCommand]
     private Task UnloadView(string param)
     {
-        return RequestUnloadAsync();
+        return RequestUnloadAsync(CancellationToken.None);
     }
 
     [ReactiveCommand]

samples/Sample.Common/ViewModelBase.cs

@@ -62,7 +62,7 @@ public virtual Task OnUnloadAsync(CancellationToken cancellationToken)
         return Task.CompletedTask;
     }
 
-    protected Task RequestUnloadAsync()
+    public Task RequestUnloadAsync(CancellationToken cancellationToken)
     {
         if (AsyncRequestUnloadEvent == null)
         {

samples/Sample.Wpf/Views/DView.xaml

@@ -46,14 +46,19 @@
         </StackPanel>
         <ScrollViewer>
             <TabControl
+                x:Name="tab"
                 an:RegionManager.PreferCache="True"
                 an:RegionManager.RegionName="TabRegion"
                 TabStripPlacement="Top">
                 <TabControl.ItemTemplate>
                     <DataTemplate>
                         <StackPanel Margin="2" Orientation="Horizontal">
                             <TextBlock VerticalAlignment="Center" Text="{Binding ViewName}" />
-                            <Button Margin="10" Content="x" />
+                            <Button
+                                Margin="10"
+                                Command="{Binding DataContext.RequestUnloadViewCommand, ElementName=tab}"
+                                CommandParameter="{Binding}"
+                                Content="x" />
                         </StackPanel>
                     </DataTemplate>
                 </TabControl.ItemTemplate>

src/AsyncNavigation/CoreExtensions.cs

@@ -113,25 +113,4 @@ public static void DisposeAll(this IEnumerable<IDisposable> disposables)
             disposable.Dispose();
         }
     }
-
-    public static NavigationContext WithParameter(this NavigationContext navigationContext, string key, object value)
-    {
-        if (navigationContext.IsCompleted && !navigationContext.IsForwordNavigation && !navigationContext.IsBackNavigation)
-            throw new InvalidOperationException("Cannot add parameters after navigation is completed.");
-
-        navigationContext.Parameters ??= new NavigationParameters();
-        navigationContext.Parameters.Add(key, value);
-        return navigationContext;
-    }
-
-    public static NavigationContext WithParameters(this NavigationContext navigationContext, IEnumerable<KeyValuePair<string, object>> parameters)
-    {
-
-        if (navigationContext.IsCompleted && !navigationContext.IsForwordNavigation && !navigationContext.IsBackNavigation)
-            throw new InvalidOperationException("Cannot add parameters after navigation is completed.");
-
-        navigationContext.Parameters ??= new NavigationParameters();
-        navigationContext.Parameters.AddRange(parameters);
-        return navigationContext;
-    }
 }

src/AsyncNavigation/NavigationContextExtensions.cs

@@ -0,0 +1,79 @@
+using AsyncNavigation.Abstractions;
+using AsyncNavigation.Core;
+using System.Diagnostics.CodeAnalysis;
+
+namespace AsyncNavigation;
+
+public static class NavigationContextExtensions
+{
+    public static bool TryResolveView(this NavigationContext navigationContext, [MaybeNullWhen(false)] out IView view)
+    {
+        if (navigationContext.Target.IsSet)
+        {
+            view = navigationContext.Target.Value!;
+            return true;
+        }
+        view = default;
+        return false;
+    }
+
+    public static bool TryResolveNavigationAware(this NavigationContext navigationContext, [MaybeNullWhen(false)] out INavigationAware aware)
+    {
+        if (navigationContext.Target.IsSet)
+        {
+            if(navigationContext.Target.Value is not null 
+                && navigationContext.Target.Value.DataContext is INavigationAware navAware)
+            {
+                aware = navAware;
+                return true;
+            }            
+        }
+        aware = default;
+        return false;
+    }
+
+    public static bool TryResolveViewAndAware(this NavigationContext navigationContext,
+        [MaybeNullWhen(false)] out IView view,
+        [MaybeNullWhen(false)] out INavigationAware aware)
+    {
+        view = default;
+        aware = default;
+
+        if (!navigationContext.Target.IsSet)
+            return false;
+
+        var target = navigationContext.Target.Value;
+        if (target is null)
+            return false;
+
+        view = target;
+
+        if (target.DataContext is INavigationAware navAware)
+        {
+            aware = navAware;
+            return true;
+        }
+        return false;
+    }
+    public static NavigationContext WithParameter(this NavigationContext navigationContext, string key, object value)
+    {
+        if (navigationContext.IsCompleted && !navigationContext.IsForwordNavigation && !navigationContext.IsBackNavigation)
+            throw new InvalidOperationException("Cannot add parameters after navigation is completed.");
+
+        navigationContext.Parameters ??= new NavigationParameters();
+        navigationContext.Parameters.Add(key, value);
+        return navigationContext;
+    }
+
+    public static NavigationContext WithParameters(this NavigationContext navigationContext, IEnumerable<KeyValuePair<string, object>> parameters)
+    {
+
+        if (navigationContext.IsCompleted && !navigationContext.IsForwordNavigation && !navigationContext.IsBackNavigation)
+            throw new InvalidOperationException("Cannot add parameters after navigation is completed.");
+
+        navigationContext.Parameters ??= new NavigationParameters();
+        navigationContext.Parameters.AddRange(parameters);
+        return navigationContext;
+    }
+
+}

src/AsyncNavigation/RegionNavigationService.cs

@@ -138,19 +138,13 @@ private async Task OnBeforeNavigationAsync(NavigationContext navigationContext)
         {
             var currentAware = (Current.Value.View.DataContext as INavigationAware)!;
             await currentAware.OnNavigatedFromAsync(navigationContext);
-            // todo: why detach?
-            //if (_regionPresenter.IsSinglePageRegion)
-            //{
-            //    _unloadHandler.Detach(currentAware);
-            //}
         }
         navigationContext.CancellationToken.ThrowIfCancellationRequested();
     }
 
     private async Task OnAfterNavigationAsync(NavigationContext navigationContext)
     {
-        if (navigationContext.Target.Value is IView view
-            && view.DataContext is INavigationAware aware)
+        if (navigationContext.TryResolveViewAndAware(out var view,out var aware))
         {
             var contextSnapshot = navigationContext;
             WeakUnloadObserver.Subscribe(aware, a =>