Follow-up for cancellation of navigation events in Blazor

src/Components/Components/src/NavigationManager.cs

@@ -303,14 +303,26 @@ protected async ValueTask<bool> NotifyLocationChangingAsync(string uri, string?
         _locationChangingCts = cts;
 
         var cancellationToken = cts.Token;
-        var context = new LocationChangingContext(uri, state, isNavigationIntercepted, cancellationToken);
+        var context = new LocationChangingContext
+        {
+            TargetLocation = uri,
+            HistoryEntryState = state,
+            IsNavigationIntercepted = isNavigationIntercepted,
+            CancellationToken = cancellationToken,
+        };
 
         try
         {
             if (handlerCount == 1)
             {
                 var handlerTask = InvokeLocationChangingHandlerAsync(_locationChangingHandlers[0], context);
 
+                if (handlerTask.IsFaulted)
+                {
+                    await handlerTask;
+                    return false; // Unreachable because the previous line will throw.
+                }
+
                 if (context.DidPreventNavigation)
                 {
                     return false;
@@ -398,17 +410,29 @@ protected async ValueTask<bool> NotifyLocationChangingAsync(string uri, string?
         }
     }
 
+    private async ValueTask InvokeLocationChangingHandlerAsync(Func<LocationChangingContext, ValueTask> handler, LocationChangingContext context)
+    {
+        try
+        {
+            await handler(context);
+        }
+        catch (OperationCanceledException)
+        {
+            // Ignore exceptions caused by cancellations.
+        }
+        catch (Exception ex)
+        {
+            HandleLocationChangingHandlerException(ex, context);
+        }
+    }
+
     /// <summary>
-    /// Invokes the provided <paramref name="handler"/>, passing it the given <paramref name="context"/>.
-    /// This method can be overridden to analyze the state of the handler task even after
-    /// <see cref="NotifyLocationChangingAsync(string, string?, bool)"/> completes. For example, this can be useful for
-    /// processing exceptions thrown from handlers that continue running after the navigation ends.
+    /// Handles exceptions thrown in location changing handlers.
     /// </summary>
-    /// <param name="handler">The handler to invoke.</param>
-    /// <param name="context">The context to pass to the handler.</param>
-    /// <returns></returns>
-    protected virtual ValueTask InvokeLocationChangingHandlerAsync(Func<LocationChangingContext, ValueTask> handler, LocationChangingContext context)
-        => handler(context);
+    /// <param name="ex">The exception to handle.</param>
+    /// <param name="context">The context passed to the handler.</param>
+    protected virtual void HandleLocationChangingHandlerException(Exception ex, LocationChangingContext context)
+        => throw new InvalidOperationException($"To support navigation locks, {GetType().Name} must override {nameof(HandleLocationChangingHandlerException)}");
 
     /// <summary>
     /// Sets whether navigation is currently locked. If it is, then implementations should not update <see cref="Uri"/> and call
@@ -420,10 +444,11 @@ protected virtual void SetNavigationLockState(bool value)
         => throw new NotSupportedException($"To support navigation locks, {GetType().Name} must override {nameof(SetNavigationLockState)}");
 
     /// <summary>
-    /// Adds a handler to process incoming navigation events.
+    /// Registers a handler to process incoming navigation events.
     /// </summary>
     /// <param name="locationChangingHandler">The handler to process incoming navigation events.</param>
-    public void AddLocationChangingHandler(Func<LocationChangingContext, ValueTask> locationChangingHandler)
+    /// <returns>An <see cref="IDisposable"/> that can be disposed to unregister the location changing handler.</returns>
+    public IDisposable RegisterLocationChangingHandler(Func<LocationChangingContext, ValueTask> locationChangingHandler)
     {
         AssertInitialized();
 
@@ -435,13 +460,11 @@ public void AddLocationChangingHandler(Func<LocationChangingContext, ValueTask>
         {
             SetNavigationLockState(true);
         }
+
+        return new LocationChangingRegistration(locationChangingHandler, this);
     }
 
-    /// <summary>
-    /// Removes a previously-added location changing handler.
-    /// </summary>
-    /// <param name="locationChangingHandler">The handler to remove.</param>
-    public void RemoveLocationChangingHandler(Func<LocationChangingContext, ValueTask> locationChangingHandler)
+    private void RemoveLocationChangingHandler(Func<LocationChangingContext, ValueTask> locationChangingHandler)
     {
         AssertInitialized();
 
@@ -505,4 +528,21 @@ private static void Validate(Uri? baseUri, string uri)
             throw new ArgumentException(message);
         }
     }
+
+    private sealed class LocationChangingRegistration : IDisposable
+    {
+        private readonly Func<LocationChangingContext, ValueTask> _handler;
+        private readonly NavigationManager _navigationManager;
+
+        public LocationChangingRegistration(Func<LocationChangingContext, ValueTask> handler, NavigationManager navigationManager)
+        {
+            _handler = handler;
+            _navigationManager = navigationManager;
+        }
+
+        public void Dispose()
+        {
+            _navigationManager.RemoveLocationChangingHandler(_handler);
+        }
+    }
 }

src/Components/Components/src/PublicAPI.Unshipped.txt

@@ -1,19 +1,23 @@
 #nullable enable
-Microsoft.AspNetCore.Components.NavigationManager.AddLocationChangingHandler(System.Func<Microsoft.AspNetCore.Components.Routing.LocationChangingContext!, System.Threading.Tasks.ValueTask>! locationChangingHandler) -> void
 Microsoft.AspNetCore.Components.NavigationManager.HistoryEntryState.get -> string?
 Microsoft.AspNetCore.Components.NavigationManager.HistoryEntryState.set -> void
 Microsoft.AspNetCore.Components.NavigationManager.NotifyLocationChangingAsync(string! uri, string? state, bool isNavigationIntercepted) -> System.Threading.Tasks.ValueTask<bool>
-Microsoft.AspNetCore.Components.NavigationManager.RemoveLocationChangingHandler(System.Func<Microsoft.AspNetCore.Components.Routing.LocationChangingContext!, System.Threading.Tasks.ValueTask>! locationChangingHandler) -> void
+Microsoft.AspNetCore.Components.NavigationManager.RegisterLocationChangingHandler(System.Func<Microsoft.AspNetCore.Components.Routing.LocationChangingContext!, System.Threading.Tasks.ValueTask>! locationChangingHandler) -> System.IDisposable!
 Microsoft.AspNetCore.Components.NavigationOptions.HistoryEntryState.get -> string?
 Microsoft.AspNetCore.Components.NavigationOptions.HistoryEntryState.init -> void
 Microsoft.AspNetCore.Components.Rendering.RenderTreeBuilder.AddContent(int sequence, Microsoft.AspNetCore.Components.MarkupString? markupContent) -> void
 Microsoft.AspNetCore.Components.Routing.LocationChangedEventArgs.HistoryEntryState.get -> string?
 Microsoft.AspNetCore.Components.Routing.LocationChangingContext
 Microsoft.AspNetCore.Components.Routing.LocationChangingContext.CancellationToken.get -> System.Threading.CancellationToken
+Microsoft.AspNetCore.Components.Routing.LocationChangingContext.CancellationToken.init -> void
 Microsoft.AspNetCore.Components.Routing.LocationChangingContext.HistoryEntryState.get -> string?
+Microsoft.AspNetCore.Components.Routing.LocationChangingContext.HistoryEntryState.init -> void
 Microsoft.AspNetCore.Components.Routing.LocationChangingContext.IsNavigationIntercepted.get -> bool
+Microsoft.AspNetCore.Components.Routing.LocationChangingContext.IsNavigationIntercepted.init -> void
+Microsoft.AspNetCore.Components.Routing.LocationChangingContext.LocationChangingContext() -> void
 Microsoft.AspNetCore.Components.Routing.LocationChangingContext.PreventNavigation() -> void
 Microsoft.AspNetCore.Components.Routing.LocationChangingContext.TargetLocation.get -> string!
+Microsoft.AspNetCore.Components.Routing.LocationChangingContext.TargetLocation.init -> void
 static Microsoft.AspNetCore.Components.CompilerServices.RuntimeHelpers.CreateInferredEventCallback<T>(object! receiver, Microsoft.AspNetCore.Components.EventCallback<T> callback, T value) -> Microsoft.AspNetCore.Components.EventCallback<T>
 static Microsoft.AspNetCore.Components.CompilerServices.RuntimeHelpers.InvokeAsynchronousDelegate(System.Action! callback) -> System.Threading.Tasks.Task!
 static Microsoft.AspNetCore.Components.CompilerServices.RuntimeHelpers.InvokeAsynchronousDelegate(System.Func<System.Threading.Tasks.Task!>! callback) -> System.Threading.Tasks.Task!
@@ -50,5 +54,5 @@ static Microsoft.AspNetCore.Components.EventCallbackFactoryBinderExtensions.Crea
 static Microsoft.AspNetCore.Components.EventCallbackFactoryBinderExtensions.CreateBinder(this Microsoft.AspNetCore.Components.EventCallbackFactory! factory, object! receiver, Microsoft.AspNetCore.Components.EventCallback<short?> setter, short? existingValue, System.Globalization.CultureInfo? culture = null) -> Microsoft.AspNetCore.Components.EventCallback<Microsoft.AspNetCore.Components.ChangeEventArgs!>
 static Microsoft.AspNetCore.Components.EventCallbackFactoryBinderExtensions.CreateBinder(this Microsoft.AspNetCore.Components.EventCallbackFactory! factory, object! receiver, Microsoft.AspNetCore.Components.EventCallback<string?> setter, string! existingValue, System.Globalization.CultureInfo? culture = null) -> Microsoft.AspNetCore.Components.EventCallback<Microsoft.AspNetCore.Components.ChangeEventArgs!>
 static Microsoft.AspNetCore.Components.EventCallbackFactoryBinderExtensions.CreateBinder<T>(this Microsoft.AspNetCore.Components.EventCallbackFactory! factory, object! receiver, Microsoft.AspNetCore.Components.EventCallback<T> setter, T existingValue, System.Globalization.CultureInfo? culture = null) -> Microsoft.AspNetCore.Components.EventCallback<Microsoft.AspNetCore.Components.ChangeEventArgs!>
-virtual Microsoft.AspNetCore.Components.NavigationManager.InvokeLocationChangingHandlerAsync(System.Func<Microsoft.AspNetCore.Components.Routing.LocationChangingContext!, System.Threading.Tasks.ValueTask>! handler, Microsoft.AspNetCore.Components.Routing.LocationChangingContext! context) -> System.Threading.Tasks.ValueTask
+virtual Microsoft.AspNetCore.Components.NavigationManager.HandleLocationChangingHandlerException(System.Exception! ex, Microsoft.AspNetCore.Components.Routing.LocationChangingContext! context) -> void
 virtual Microsoft.AspNetCore.Components.NavigationManager.SetNavigationLockState(bool value) -> void

src/Components/Components/src/Routing/LocationChangingContext.cs

@@ -6,38 +6,30 @@ namespace Microsoft.AspNetCore.Components.Routing;
 /// <summary>
 /// Contains context for a change to the browser's current location.
 /// </summary>
-public class LocationChangingContext
+public sealed class LocationChangingContext
 {
-    internal LocationChangingContext(string targetLocation, string? historyEntryState, bool isNavigationIntercepted, CancellationToken cancellationToken)
-    {
-        TargetLocation = targetLocation;
-        HistoryEntryState = historyEntryState;
-        IsNavigationIntercepted = isNavigationIntercepted;
-        CancellationToken = cancellationToken;
-    }
-
     internal bool DidPreventNavigation { get; private set; }
 
     /// <summary>
     /// Gets the target location.
     /// </summary>
-    public string TargetLocation { get; }
+    public required string TargetLocation { get; init; }
 
     /// <summary>
     /// Gets the state associated with the target history entry.
     /// </summary>
-    public string? HistoryEntryState { get; }
+    public string? HistoryEntryState { get; init; }
 
     /// <summary>
     /// Gets whether this navigation was intercepted from a link.
     /// </summary>
-    public bool IsNavigationIntercepted { get; }
+    public bool IsNavigationIntercepted { get; init; }
 
     /// <summary>
     /// Gets a <see cref="System.Threading.CancellationToken"/> that can be used to determine if this navigation was canceled
     /// (for example, because the user has triggered a different navigation).
     /// </summary>
-    public CancellationToken CancellationToken { get; }
+    public CancellationToken CancellationToken { get; init; }
 
     /// <summary>
     /// Prevents this navigation from continuing.