NavigationError on NavigateTo - asp.net-core

Question

I'm trying out Blazor ServerSide and created a Component to Redirect To the Login Page when a user is not logged in.
#inject Microsoft.AspNetCore.Components.NavigationManager NavigationManager;
#code {
/// <inheritdoc />
protected override Task OnInitializedAsync()
{
NavigationManager.NavigateTo("Login");
return Task.CompletedTask;
}
}
But always when "NavigateTo" is called the following exception is thrown:
"Microsoft.AspNetCore.Components.NavigationException: Exception of type 'Microsoft.AspNetCore.Components.NavigationException' was thrown.
at Microsoft.AspNetCore.Components.Server.Circuits.RemoteNavigationManager.NavigateToCore(String uri, Boolean forceLoad)
at Microsoft.AspNetCore.Components.NavigationManager.NavigateTo(String uri, Boolean forceLoad)
at ApplySupportTool.Blazor.Pages.RedirectToLogin.OnInitializedAsync() in C:\\Users\\padruttn\\Documents\\git\\ApplySupportTool\\src\\ApplySupportTool.Blazor\\Pages\\RedirectToLogin.razor:line 8"
Interesstingly the navigation is made despite the exception.
I also tried to call it with the path "/login" but the same behaviour here.

Answer 1

There is an open issue on github for this problem. See also the preceeding issue where a possible workaround is mentioned: putting the NavigateTo method into OnAfterRender instead of OnInitialized.

Answer 2

I needed to put this into OnInitialized rather than OnAfterRender, so had to go with the render-mode="Server" method, though apparently this isn't recommended.
It also states in the GitHub issue that this only happens in debug, not release, so a middle ground option is to change _Host.cshtml to contain:
<environment include="Staging,Production">
<component render-mode="ServerPrerendered" type="typeof(App)" />
</environment>
<environment include="Development">
<component render-mode="Server" type="typeof(App)" />
</environment>

Answer 3

Note that the following may be considered a workaround:
You may also change your method to the following including the "async" keyword to its signature, there is going to be a complaint about not using await, but in exchange you are not going to need a return value. Since it doesn't have an 'await' the effect is kinda the same as the synchronous version, but without the exception being thrown.
protected override async Task OnInitializedAsync()
{
NavigationManager.NavigateTo("Login");
}
Here is an example where i am using a RedirectToLogin.razor component in my routing
#inject NavigationManager NavigationManager
#code{
protected override async Task OnInitializedAsync()
{
var returnUrl = "~/" + NavigationManager.ToBaseRelativePath(NavigationManager.Uri);
NavigationManager.NavigateTo($"Identity/Account/Login?returnUrl={returnUrl}", forceLoad:false);
}
}
And in my App.razor
<Found Context="routeData">
<AuthorizeRouteView RouteData="#routeData" DefaultLayout="#typeof(MainLayout)">
<NotAuthorized>
<RedirectToLogin />
</NotAuthorized>
</AuthorizeRouteView>
</Found>

Answer 4

Old post, but - if you are running a Blazor Server app, this behavior only happens if render-mode is "ServerPrerendered". Disabling Pre-rendering by changing the mode to "Server" makes the exception not be thrown in the first place:
<app>
<component type="typeof(App)" render-mode="Server" />
</app>
I've searched current Blazor Documentation and change notes, and haven't found any mention of this, so just in case it helps somebody else...

Answer 5

I ran into the same problem and filed issue #28355. The official answer is, that it is save to ignore the exception when NaviagteTo is placed in OnInitialized. Here is the answer from javiercn:
Yes, it is completely safe to ignore it. The debugger stops because it is configured to do so, but in this case the exception is always handled. You can turn-off breaking on this exception if it's caught on the debugger settings.
Issue #13582 deals with how to prevent the debugger from stopping at this exception.

Answer 6

use OnInitializedAsync replace OnInitialized
protected override async Task OnInitializedAsync()
{
nav.NavigateTo("/login", true);
await base.OnInitializedAsync();
}

Answer 7

I had this when I tried to call the navigateto from another thread. render-mode = "Server" - solved the problem

Answer 8

In .NET 5.0, in the _host.cshtml file. Past the following #(await Html.RenderComponentAsync(RenderMode.Server)) in the line after the "blazor_error_ui" section.