Can I lookup the list of routes for a nominated page?

Question

I have code similar to the following:

@page "/somepage/{Id:guid}/add"
@page "/somepage/{Id:guid}/remove"

@inject NavigationManager navigationManager
@implements IAsyncDisposable

if ( @remove ) {
    <div>Remove!</div>
} else {
    <div>Add!</div>
}

@code{
    [Parameter]
    public Guid Id { get; set; }

    protected override void OnInitialized()
    {
        navigationManager.LocationChanged += HandleLocationChanged;
    }

    public async ValueTask DisposeAsync()
    {
        navigationManager.LocationChanged -= HandleLocationChanged;
    }

    protected override async Task OnParametersSetAsync()
    {
        remove = navigationManager.Uri.Contains("remove");

        // Load some data...

        await base.OnParametersSetAsync();
    }

    private void HandleLocationChanged(object? sender, LocationChangedEventArgs e)
    {
        var pageUris = new[] {
            $"/somepage/{Id}/add",
            $"/somepage/{Id}/remove"
        };

        var uri = navigationManager.Uri.Replace( navigationManager.BaseUri, "" );

        if ( !pageUris.Contains(uri) ) return;

        remove = navigationManager.Uri.Contains("remove");

        // Load some data...

        StateHasChanged();
    }
}

In the HandleLocationChanged event, I realised that if the user clicks on a link to a completely different page, then data will be loaded for the wrong page. So I added a guard to check NavigationManager.Uri - to see if it points to a different location.

Is there some way to make this more generic? For example, can I get a list of routes for a particular page and then use that in my comparison?

Answer 1

Your question asks how to replace your hardcoded pageUris variable:

var pageUris = new[] {
    $"{navigationManager.BaseUri}somepage/add",
    $"{navigationManager.BaseUri}somepage/remove"
};

Knowing that @page "/foo" results in a [RouteAttribute("foo")] being applied to your page's generated class, it's straightforward to create a function that will replace your code:

private string[] GetPageUrls()
{
    return GetType().GetCustomAttributes<RouteAttribute>().Select(x => x.Template).ToArray();
}

This will produce one element for each @page directive you have, containing the values:

"/somepage/add", "/somepage/remove"

In your question, you combine it with navigationManager.BaseUri which I believe should not be necessary, since by default a Blazor app sets the base url (i.e. <base href="/" />), but if you want that returned, it's obviously trivial to change GetPageUrls to incorporate that as well.

Finally, if you want to use this elsewhere, it should be straightforward to convert this into an extension method.