tracks form changes and warns users before navigation

WebApp/Components/Features/Events/Edit.razor

@@ -18,6 +18,7 @@
     BackButtonUrl="/events" />
 
 <EditForm id="edit-event-form" Model="EventDefinition" OnValidSubmit="OnValidSubmit" Enhance>
+    <FormChangeTracker @ref="_formChangeTracker" />
     <AntiforgeryToken />
     <DataAnnotationsValidator />
     <MudGrid>
@@ -55,7 +56,7 @@
 
 <FormActions>
     <MudButton ButtonType="ButtonType.Submit" Variant="Variant.Filled" Color="Color.Primary" Form="edit-event-form">Save</MudButton>
-    <MudButton Href="/events" Variant="Variant.Text">Cancel</MudButton>
+    <MudButton OnClick="HandleCancel" Variant="Variant.Text">Cancel</MudButton>
 </FormActions>
 
 @code {
@@ -65,6 +66,8 @@
     [SupplyParameterFromForm]
     private EventDefinition? EventDefinition { get; set; }
 
+    private FormChangeTracker? _formChangeTracker;
+
     protected override async Task OnInitializedAsync()
     {
         EventDefinition ??= await context.Events.FirstOrDefaultAsync(m => m.Id == Id);
@@ -84,6 +87,8 @@
         try
         {
             context.SaveChangesAsync();
+            _formChangeTracker?.AllowNavigation();
+            NavigationManager.NavigateTo("/events");
         }
         catch (DbUpdateConcurrencyException)
         {
@@ -96,7 +101,11 @@
                 throw;
             }
         }
+    }
 
+    private void HandleCancel()
+    {
+        _formChangeTracker?.AllowNavigation();
         NavigationManager.NavigateTo("/events");
     }