Track location in background

[alefcarlos]

Using HostedService to track user location is not a possibility, is there any way to track the location in background using blazor ?

I would like to invoke a SignalR method on OnPositionRecieved.

[IEvangelist]

Is the idea to have this be something that tracks the position with the server or wasm approach?

[alefcarlos]

@IEvangelist, actually, event after the clear the callback is fired. I'm trying this now. Is this the expected behaviour ?

protected override async Task OnAfterRenderAsync(bool firstRender)
{
    if (firstRender is false)
    {
        return;
    }

    _watchId =  await Geolocation.WatchPositionAsync(
        component: this,
        onSuccessCallbackMethodName: nameof(OnPositionReceived),
        onErrorCallbackMethodName: nameof(OnPositionError),
        options: _options);
}

[JSInvokable]
public void OnPositionReceived(GeolocationPosition position)
{
    _isLoading = false;
    _position = position;
    StateHasChanged();
}

[JSInvokable]
public void OnPositionError(GeolocationPositionError positionError)
{
    _isLoading = false;
    _positionError = positionError;
    StateHasChanged();
}

public async ValueTask DisposeAsync()
{
    await Geolocation.ClearWatchAsync(_watchId);
}

[alefcarlos]

I got the point, the DisposeAsync was throwing exception:

fail: Microsoft.AspNetCore.Server.Kestrel[13]
      Connection id "0HN3EK0DEPNV3", Request id "0HN3EK0DEPNV3:00000005": An unhandled exception was thrown by the application.
      System.InvalidOperationException: JavaScript interop calls cannot be issued at this time. This is because the component is being statically rendered. When prerendering is enabled, JavaScript interop calls can only be performed during the OnAfterRenderAsync lifecycle method.
         at Microsoft.AspNetCore.Components.Server.Circuits.RemoteJSRuntime.BeginInvokeJS(Int64 asyncHandle, String identifier, String argsJson, JSCallResultType resultType, Int64 targetInstanceId)
         at Microsoft.JSInterop.JSRuntime.InvokeAsync[TValue](Int64 targetInstanceId, String identifier, CancellationToken cancellationToken, Object[] args)
         at Microsoft.JSInterop.JSRuntime.InvokeAsync[TValue](Int64 targetInstanceId, String identifier, Object[] args)
         at Microsoft.JSInterop.JSRuntimeExtensions.InvokeVoidAsync(IJSRuntime jsRuntime, String identifier, Object[] args)
         at Hbsa.Acqua.Geo.Components.Pages.Geo.DisposeAsync() in C:\repos\dev.azure.com\hidrovias-brasil\acqa-poc-blazor-embedded\src\gps_server\Hbsa.Acqua.Geo\Components\Pages\Geo.razor.cs:line 53
         at Microsoft.AspNetCore.Components.RenderTree.Renderer.<>c__DisplayClass85_0.<<Dispose>g__HandleAsyncExceptions|1>d.MoveNext()
      --- End of stack trace from previous location ---
         at Microsoft.AspNetCore.Components.RenderTree.Renderer.<>c__DisplayClass85_0.<<Dispose>g__HandleAsyncExceptions|1>d.MoveNext()
      --- End of stack trace from previous location ---
         at Microsoft.AspNetCore.Components.RenderTree.Renderer.DisposeAsync()
         at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngineScope.<DisposeAsync>g__Await|26_0(Int32 i, ValueTask vt, List`1 toDispose)
         at Microsoft.AspNetCore.Http.Features.RequestServicesFeature.<DisposeAsync>g__Awaited|9_0(RequestServicesFeature servicesFeature, ValueTask vt)
         at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http.HttpProtocol.<FireOnCompleted>g__ProcessEvents|242_0(HttpProtocol protocol, Stack`1 events)

[IEvangelist]

Let me try it locally, and report back... I'd expect that to work. If it doesn't, and the App is disposed, you could create a slightly different approach. You could have a background service that listens for changes, and an API that accepts the changes. You could then use session storage with a new Guid to act as a client ID that corresponds to location updates.

[IEvangelist]

So, locally... I'm testing this now, and it is working as I'd expect. See: https://github.com/IEvangelist/blazorators/blob/main/samples/BlazorServer.ExampleConsumer/Pages/Track.razor.cs. This sample code, is server-based and while the app is running and, on this page, it works as expected. If you're trying to track at the App level, that's not something I've done but I'd be curious why would you need that?

In other words, when your Geo page goes out of scope it is disposed thus stopping the geolocation callbacks.

[alefcarlos]

I was using that example. I have at least 5 pages that needs the geolocalization, and I was thinking about creating a backgroundservice to set a singleton instance with the current position and use that singleton into the pages, just to reduce code.

So the best approach is to implement the GetCurrentPosition on each page, right ?