RESOLVED: Clearing the display of trackPolygons

Question

Original User: Scole

I have a tool in an add-in in which the user draws a polygon on the screen using trackPolygon and then the geometry of the polygon is used to query another data layer. This all works just fine but as the add-in is used multiple times, the display gets cluttered with multiple polygons.

How can I flush the display to remove any previously drawn polygons? I tried inserting Application.ActiveMapDisplay.CancelTracking into my code either at the beginning or end of my code (an onClick event) but it does not appear to do anything.

Thanks!
Steve

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Anonymous User · Answer

Original User: aaronnoriegaahh thanks very much, yeah def still learning. have left ole VB and began using C# aww sooo much better!!!. Now I am still a bit stuck though looking at the Mapdisplay.graphics trying to pull a particular item from the Collection. still trying to figure out the Contains method kinda of seems 'not too powerful' I guess if you need to move it comes in help. Also doesn't look like you can use LINQ against the collection either??? Brian want-to-be-programmer I haven't tested this code, but this should give you a general idea on how to employ LINQ to query graphic attributes public class WidgetItem{//user class to define associated attributes to Graphic Objects public string Name { get; set; } public DateTime DateAdded { get; set; } public Graphic Graphic { get; set; } public WidgetItem (){ this.DateAdded = DateTime.Now; } } List widgets = new List(); // Create and populate Widget Objects WidgetItem wi = new WidgetItem(); wi.Name = "Brian"; wi.Graphic = somegraphic; //probably the result of a track() operation widgets.Add(wi); var removeus = (from w in widgets where w.Name.StartsWith("B") && w.Graphic != null select w.Graphic); ActiveMapDisplay.Graphics.Remove(removeus); You can further increase the capabilities of the WidgetItem class by implementing the IComparable and IEquatable templates; as well as overriding the GetHashCode and Equals functions.

BrianLocke · Answer

ahh thanks very much, yeah def still learning. have left ole VB and began using C# aww sooo much better!!!.  Now I am still a  bit stuck though looking at the Mapdisplay.graphics trying to pull a particular item from the Collection.  still trying to figure out the Contains method kinda of seems 'not too powerful' I guess if you need to move it comes in help.  Also doesn't look like you can use LINQ against the collection either???

Brian 
want-to-be-programmer

Anonymous User · Answer

Original User: BorseleCountyCouncil

Brian,
Because of the way iterators/enumerators work in .Net, you can't safely change the list while you're going through it.
It's a bit like working through a linked list, deleting the current element and then using it's next pointer to move on.

Here are 2 workarounds:
1. Work backwards : for (int i = list.Count - 1; i >= 0; --i) list.RemoveAt(i);

2. Create a temporary list in which you place the elements to delete while iterating. When finished iterating, call the list function which removes all elements given an enumerator (your delete list).

Hope this helps.