How do you limit the map extent in ArcGIS Runtime .NET 100.2

[NathanRaley]

How can you set the maximum extent for the MapView in the .NET runtime version 100.2?

I've tried intercepting the OnViewPointChanged, but my viewpoint doesn't exactly match the bounds that I had set, I am assuming due to the zoom level scaling or something of that nature?

So then I tried on my setup, 

Snippet

            // Set the current viewpoint/extent of the map and animate to it            await SetViewpointGeometryAsync(MapBounds).ContinueWith((prevTask) =>            {                 _viewPointBounds = GetCurrentViewpoint(ViewpointType.BoundingGeometry).TargetGeometry;                 _prevBounds = _viewPointBounds;             });

and on my event handler:

Snippet

private void OnViewPointChanged(object sender, EventArgs e) {     var newBounds = GetCurrentViewpoint(ViewpointType.BoundingGeometry).TargetGeometry;       if (!GeometryEngine.Within(newBounds, _viewPointBounds))         SetViewpoint(new Viewpoint(_prevBounds));     else        _prevBounds = newBounds; }

This works great for the first time I load the map, but when I set up the map for another view, it ends up stuck at the old one, despite my _viewPointBounds and _prevBounds being reset via the code above in the setup that is called again.

Any ideas?  I feel like I am pretty close, but I'm just missing something.

[MarkCollins]

Did you ever find a solution to this? I'm trying to do the same thing.

[NathanRaley]

None that provided a descent user experience.  It was very choppy and inconsistent.

[MatthiasPorges]

Not nice, but works. Also seems pretty smooth. Probably good enough for production.

Define an envelope:

private Envelope _bounds=
    new Envelope(
        new MapPoint(MAP_BOX_WEST, MAP_BOX_NORTH, SpatialReferences.WebMercator),
        new MapPoint(MAP_BOX_EAST, MAP_BOX_SOUTH, SpatialReferences.WebMercator));

Now make a polygon as well, because some GeometryEngine operations don't work with Envelopes for some reason:

private Polygon _boundsPolygon = EnvelopeToPolygon(_envelope);

private static Polygon EnvelopeToPolygon(Envelope envelope)
{
    return new Polygon(new MapPoint[]
    {
        new MapPoint(envelope.XMin, envelope.YMin, SpatialReferences.WebMercator),
        new MapPoint(envelope.XMax, envelope.YMin, SpatialReferences.WebMercator),
        new MapPoint(envelope.XMax, envelope.YMax, SpatialReferences.WebMercator),
        new MapPoint(envelope.XMin, envelope.YMax, SpatialReferences.WebMercator)
    });
}

Finally add a ViewpointChanged event:

private void MapView_ViewpointChanged(object sender, EventArgs e)
{
    var selected = (MapPoint)MapView.GetCurrentViewpoint(ViewpointType.CenterAndScale).TargetGeometry;
    bool legal = GeometryEngine.Contains(_bounds, selected);

    if (!legal)
    {
        SetViewpoint(GeometryEngine.NearestCoordinate(_boundsPolygon, selected).Coordinate);
        return;
    }
}

This method changes the viewpoint back to a legal state. Also prevents user interaction during the animation.

private async void SetViewpoint(MapPoint point)
{
    MapView.InteractionOptions.IsEnabled = false;   //Make sure to initialize MapView.InteractionOptions to avoid NullReferenceException
    await MapView.SetViewpointCenterAsync(point);
    MapView.InteractionOptions.IsEnabled = true;
}

[NathanRaley]

Yes, we were trying something like that.  However, since it is on the "changed" event and not a "changing", we were receiving some very weird rubber banding since the viewpoint had already changed and started rendering as opposed to intercepting it prior to the change/render.