Add support for watchPosition

[dpaquette]

The watchPosition method seems useful. We should support it.
https://developer.mozilla.org/en-US/docs/Web/API/Geolocation/watchPosition

[dpaquette]

I got this working on the plane. I will try to get it checked in and published soon

[dpaquette]

This is done. I just need to update the Readme with a sample so people know how to use it

[joseftw]

Hello!
Im trying to get the WatchLocation feature to work, but it seems like it never fires, my breakpoint in OnWatchLocationCallback is never hit. Have I missed something obvious?
GetLocationAsync works like a charm :)

@functions
{
    private string _position = string.Empty;
    Location _location;

    protected override async Task OnInitAsync()
    {
        await LocationService.WatchLocation(OnWatchLocationCallback);
        _location = await LocationService.GetLocationAsync();
    }

    private void OnWatchLocationCallback(Location obj)
    {
        _position = $"{obj.Latitude} - {obj.Longitude} - {obj.Accuracy}";
    }
}

[soend]

Hello!
Im trying to get the WatchLocation feature to work, but it seems like it never fires, my breakpoint in OnWatchLocationCallback is never hit. Have I missed something obvious?
GetLocationAsync works like a charm :)

@functions
{
    private string _position = string.Empty;
    Location _location;

    protected override async Task OnInitAsync()
    {
        await LocationService.WatchLocation(OnWatchLocationCallback);
        _location = await LocationService.GetLocationAsync();
    }

    private void OnWatchLocationCallback(Location obj)
    {
        _position = $"{obj.Latitude} - {obj.Longitude} - {obj.Accuracy}";
    }
}

Hello,

Did you end up figuring this out? I tried it also and it only seemed to work when i call the WatchLocation method from OnAfterRenderAsync override.
Example:

    protected override async Task OnAfterRenderAsync(bool firstRender)
    {
        await LocationService.WatchLocation(OnWatchLocationCallback);
        StateHasChanged();
    }