tracks form changes and warns users before navigation

WebApp/Components/Features/Events/Create.razor

@@ -11,6 +11,7 @@
     BackButtonUrl="/events" />
 
 <EditForm id="create-event-form" Model="EventDefinition" OnValidSubmit="OnValidSubmit" Enhance>
+    <FormChangeTracker @ref="_formChangeTracker" />
     <AntiforgeryToken />
     <DataAnnotationsValidator />
     <MudGrid>
@@ -48,17 +49,27 @@
 
 <FormActions>
     <MudButton ButtonType="ButtonType.Submit" Variant="Variant.Filled" Color="Color.Primary" Form="create-event-form">Create</MudButton>
-    <MudButton Href="/events" Variant="Variant.Text">Cancel</MudButton>
+    <MudButton OnClick="HandleCancel" Variant="Variant.Text">Cancel</MudButton>
 </FormActions>
 
 @code {
     [SupplyParameterFromForm]
     private EventDefinition EventDefinition { get; set; } = new();
 
+    private FormChangeTracker? _formChangeTracker;
+
     private void OnValidSubmit()
     {
+        _formChangeTracker?.AllowNavigation();
+
         context.Events.Add(EventDefinition);
         context.SaveChanges();
         NavigationManager.NavigateTo("/events");
     }
+
+    private void HandleCancel()
+    {
+        _formChangeTracker?.AllowNavigation();
+        NavigationManager.NavigateTo("/events");
+    }
 }