System.ArgumentException 'An item with the same key has already been added'

Question

How can I diagnose the above exception? In my code, I roughly do the following:

1. Create an overlay ( overlay = new GraphicsOverlay() )

2. Create a set of polygons ( poly = new Polygon(mappoints) where mappoints is a PointCollection)

3. Create a graphic with the polygon geometry and a simple fill symbol for each polygon

( graphic = new Graphic() { Geometry = poly, Symbol = new SimpleFillSymbol() { Color = Colors.Red } } )

4. Add that graphic to the overlay. ( overlay.Add(graphic) )

Then, when something changes, I will call overlay.Graphics.Clear(), then repeat steps 2-3.

When I do this, sometimes on the new Graphic(...), I will get the exception (but not every time)

I'm using Esri.ArcGISRuntime version 100.0.0.0.

Any idea what's going on?

SomeGISGuy · Answer

> Really I am mostly anxious about a new version of the control. It's been 6 months

We're generally shipping out 2 releases a year, and the next one is right around the corner. And it's "only" been 4 months since 100.2.1 released 🙂

And we're probably/hopefully/planning to be shipping 3 releases this year...

AFAIK this issue was resolved a while ago. Are you still seeing it with v100.2.1 ?

andybeaulieu · Answer

In our case, the WaitForPendingFinalizers() call was freezing the whole app in some situations. Probably something unique to a particular situation and what the garbage collector had to do.

Really I am mostly anxious about a new version of the control. It's been 6 months

But if anyone else hits this specific issue, this is the general workaround that we used instead of GC.Collect.. Basically just kept a list of Graphics and instead of Clear()'ing them, we re-use...

// first keep a cache of Graphics.
 private List<Graphic> RouteGraphics { get; set; }

{...}

// later on when creating geometries... Re-use items from the Cache

// so you don't need to Clear()

Polyline newPolyLine = new Polyline(mapPoints);
 if (RouteGraphics.Count > routeGraphicIndex)
 {
 // we will re-use an existing Route Graphic
 Graphic routeGraphicExisting = RouteGraphics[routeGraphicIndex];
 routeGraphicExisting.Geometry = newPolyLine;
 routeGraphicExisting.IsVisible = true;
 }
 else
 {
 // we will create a new Route Graphic
 SimpleLineSymbol lineSymbol = new SimpleLineSymbol(SimpleLineSymbolStyle.Solid, lineColor, 3.0);
 Graphic routeGraphicNew = new Graphic(newPolyLine, lineSymbol);
 //System.Diagnostics.Debug.WriteLine(" Adding routeGraphicNew");
 MapOverlay.Graphics.Add(routeGraphicNew);
 RouteGraphics.Add(routeGraphicNew);
 }

routeGraphicIndex++;

AndyWright · Answer

This works for us 99.9% of the time.  Every once in a while one of these errors slips through the lines of defense, but they are very rare since we implemented this.

GC.Collect();
 GC.WaitForPendingFinalizers();
 GC.Collect();