Added new kb article form-prompt-unsaved-changes

Author: KB Bot

knowledge-base/form-prompt-unsaved-changes.md

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+---
+title: How to Prompt Users for Unsaved Changes on Navigation
+description: A guide on how to implement a warning for unsaved changes when attempting to navigate away from a TelerikForm in Blazor applications.
+type: how-to
+page_title: How to Prompt Users for Unsaved Changes in Blazor TelerikForm
+slug: form-kb-prompt-unsaved-changes
+tags: blazor, form, navigation, unsaved changes
+res_type: kb
+ticketid: 1682122, 1629951
+---
+
+## Environment
+
+<table>
+	<tbody>
+		<tr>
+			<td>Product</td>
+			<td>Form for Blazor</td>
+		</tr>
+	</tbody>
+</table>
+
+## Description
+
+This knowledge base article answers the following questions:
+
+- How to detect unsaved changes in a Blazor TelerikForm?
+- How to prompt users before navigating away from unsaved changes in Form?
+- How to conditionally navigate away from a form?
+
+## Solution
+
+To prompt the users with a warning message when they attempt to navigate away from a page with unsaved changes in a TelerikForm, follow these steps:
+
+1. Inject [`NavigationManager`](https://learn.microsoft.com/en-us/aspnet/core/blazor/fundamentals/routing?view=aspnetcore-7.0#handleprevent-location-changes) to handle navigation
+2. Register a handler using `NavigationManager.RegisterLocationChangingHandler()` to intercept navigation attempts
+3. In [`LocationChangingHandler`](https://www.telerik.com/blogs/blazor-new-locationchanging-events-dotnet-7), check if the form has unsaved changes
+4. Add a [`<TelerikDialog>`](slug:dialog-overview) to prompt the user when there are unsaved changes
+5. Implement a `PreventLeaving()` method and `ProceedNavigation()` method to close the dialog without navigating and to manually navigate to the stored URL if the user confirms
+
+`````RAZOR
+@implements IDisposable
+@inject NavigationManager NavigationManager
+
+<TelerikForm @ref="@FormRef"
+             Model="@Employee"
+             Width="300px">
+    <FormItems>
+        <FormItem Field="@nameof(Person.Id)" Enabled="false"></FormItem>
+        <FormAutoGeneratedItems />
+    </FormItems>
+</TelerikForm>
+
+<NavLink href="test">Go To Other Page</NavLink>
+
+<TelerikDialog @bind-Visible="@ShowNavigationDialog"
+               Title="Confirm Navigation">
+    <DialogContent>
+        You have unsaved changes. Are you sure you want to leave this page?
+    </DialogContent>
+    <DialogButtons>
+        <TelerikButton OnClick="@PreventLeaving">No</TelerikButton>
+        <TelerikButton ThemeColor="primary" OnClick="@ProceedNavigation">Yes</TelerikButton>
+    </DialogButtons>
+</TelerikDialog>
+
+@code {
+    private Person Employee = new Person();
+    private TelerikForm? FormRef { get; set; }
+    private IDisposable? NavEventRegistration;
+    private bool ShowNavigationDialog = false;
+    private string? NextUrl;
+    private bool isNavigationConfirmed = false; // Flag to track navigation confirmation
+
+    private ValueTask LocationChangingHandler(LocationChangingContext args)
+    {
+        // Prevent the confirmation dialog from appearing again once the user confirmed navigation
+        if (isNavigationConfirmed)
+        {
+            return ValueTask.CompletedTask;
+        }
+
+        if (FormRef?.EditContext.IsModified() ?? false)
+        {
+            // Prevent navigation and store the target URL
+            args.PreventNavigation();
+            NextUrl = args.TargetLocation;
+            ShowNavigationDialog = true;
+
+            // Force Blazor to re-render
+            InvokeAsync(StateHasChanged);
+        }
+
+        return ValueTask.CompletedTask;
+    }
+
+    private void PreventLeaving()
+    {
+        // Simply close the dialog without changing the page
+        ShowNavigationDialog = false;
+        StateHasChanged();
+    }
+
+    private void ProceedNavigation()
+    {
+        // Set the flag to indicate navigation is confirmed
+        isNavigationConfirmed = true;
+
+        // Navigate manually to the stored target URL
+        if (!string.IsNullOrEmpty(NextUrl))
+        {
+            NavigationManager.NavigateTo(NextUrl);
+        }
+
+        // Close the dialog after confirming navigation
+        ShowNavigationDialog = false;
+    }
+
+    protected override void OnInitialized()
+    {
+        Employee = new Person()
+            {
+                Id = 1,
+                FirstName = "John",
+                LastName = "Doe",
+                BirthDate = DateTime.Today.AddYears(-30)
+            };
+
+        // Register the navigation handler
+        NavEventRegistration = NavigationManager.RegisterLocationChangingHandler(LocationChangingHandler);
+    }
+
+    public void Dispose()
+    {
+        NavEventRegistration?.Dispose();
+    }
+
+    public class Person
+    {
+        public int Id { get; set; }
+        public string FirstName { get; set; } = string.Empty;
+        public string LastName { get; set; } = string.Empty;
+        public DateTime BirthDate { get; set; } = DateTime.Today;
+    }
+}
+`````
+
+## See Also
+
+- [Blazor Form Overview](slug:form-overview)
+- [Blazor Dialog Overview](slug:dialog-overview)