NavigationError on NavigateTo

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.

Solution 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.

Solution 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>

Solution 3

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>

Solution 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...

Solution 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.

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