unoplatform/uno · error · InvalidOperationException

Unable to find [LayerGrid] template part

Error message

Unable to find [LayerGrid] template part

What it means

InvalidOperationException thrown by MapPresenter.OnApplyTemplate (iOS) when GetTemplateChild("LayerGrid") does not return a Grid. Same required template-part contract as the Android LayerGrid (error 27); the iOS presenter needs it for overlay layers.

Source

Thrown at src/AddIns/Uno.UI.Maps/MapPresenter.iOS.cs:53

		private MapControl? _owner;

		protected override void OnApplyTemplate()
		{
			base.OnApplyTemplate();
			UpdateOwnerSubscriptions();

			_mapGrid = GetTemplateChild("MapGrid") as Grid;
			_layerGrid = GetTemplateChild("LayerGrid") as Grid;

			if (_mapGrid == null)
			{
				throw new InvalidOperationException("Unable to find [MapGrid] template part");
			}

			if (_layerGrid == null)
			{
				throw new InvalidOperationException("Unable to find [LayerGrid] template part");
			}

			_internalMapView = new MKMapView();

			_mapGrid.Children.Add(_internalMapView);
			_internalMapView.ShowsUserLocation = false;

			_internalMapView.RegionChanged += OnRegionChanged;

			OnChildrenCollectionChanged(this, null);

			SetUpOverlayRenderer();

			_internalMapView.GetViewForAnnotation = OnGetViewForAnnotation!;
		}

		private IDisposable UpdateOwnerSubscriptions(MapControl owner)
		{

View on GitHub (pinned to 0418340488)

Solutions

  1. Ensure <Grid x:Name="LayerGrid"/> (type Grid) is present in the template on iOS.
  2. Mirror the default Generic.xaml template and only restyle non-structural elements.
  3. Confirm element type is Grid, not Canvas/Border.
  4. Revert to default template to confirm root cause is the custom template.

Example fix

// before
<Border x:Name="LayerGrid"/>

// after
<Grid x:Name="LayerGrid"/>
Defensive patterns

Strategy: validation

Validate before calling

var layerGrid = mapControl.GetTemplateChild("LayerGrid") as Grid;
if (layerGrid == null) throw new InvalidOperationException("Custom template missing LayerGrid (iOS)");

Type guard

bool TemplateHasLayerGrid(Control c)
    => c.GetTemplateChild("LayerGrid") is Grid;

Try / catch

try { /* OnApplyTemplate logic */ }
catch (InvalidOperationException ex) when (ex.Message.Contains("LayerGrid"))
{ Log.Error("MapControl (iOS) template missing LayerGrid part"); }

Prevention

When it happens

Trigger: Custom ControlTemplate for MapControl on iOS omits the 'LayerGrid' Grid or uses a non-Grid element named 'LayerGrid', causing the 'as Grid' cast to return null.

Common situations: Cross-platform shared Style that defines LayerGrid as a different panel; theme override dropping the named element; renaming during refactoring.

Related errors

AI-assisted analysis of unoplatform/uno@0418340488 (2026-08-13). Data as JSON: /api/errors/68529239ad7820f5. Report an issue: GitHub.