# WorldMapKitWmsWpfOverlay throws null exception when setting IsVisible **URL:** \ **Category:** WPF\ **Created:** [August 2, 2010, 10:58pm UTC](https://community.thinkgeo.com/t/worldmapkitwmswpfoverlay-throws-null-exception-when-setting-isvisible/2763 "2010-08-02T22:58:01Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![Klaus3](https://community.thinkgeo.com/letter_avatar_proxy/v4/letter/k/e5b9ba/32.png) [@Klaus3](https://community.thinkgeo.com/u/Klaus3)\ **Post date:** [August 2, 2010, 10:58pm UTC](https://community.thinkgeo.com/t/worldmapkitwmswpfoverlay-throws-null-exception-when-setting-isvisible/2763/1 "2010-08-02T22:58:01Z")
 Guys,  Just some minor issues I have run into. You may have fixed them or there is a reason behind these behaviors.  No worries as I have ways around them. 1. If you try setting the IsVisible property of a WorldMapKitWmsWpfOverlay it throws a null argument exception.    2. Calling WpfMap.ZoomToPreviousExtent fires OnMapExtentChanging event twice. Thanks, K   ---
**Author:** ![Howard](https://community.thinkgeo.com/letter_avatar_proxy/v4/letter/h/90ced4/32.png) [@Howard](https://community.thinkgeo.com/u/Howard)\ **Post date:** [August 3, 2010, 12:23am UTC](https://community.thinkgeo.com/t/worldmapkitwmswpfoverlay-throws-null-exception-when-setting-isvisible/2763/2 "2010-08-03T00:23:12Z")
Hi Klaus,      As I tested, when I set WorldMapKitWmsWpfOverlay to invisible, it doesn’t throw exception; I just did a simple test; could you show me the code you are using? For your second issue, I think you might mean CurrentExtentChanging event. I cannot recreate this issue neither with our latest Dll. Please try the latest Dll and try or show us you code so that I can recreate it.      Thanks for reporting this.   Howard ---
**Author:** ![Klaus3](https://community.thinkgeo.com/letter_avatar_proxy/v4/letter/k/e5b9ba/32.png) [@Klaus3](https://community.thinkgeo.com/u/Klaus3)\ **Post date:** [August 3, 2010, 4:21pm UTC](https://community.thinkgeo.com/t/worldmapkitwmswpfoverlay-throws-null-exception-when-setting-isvisible/2763/3 "2010-08-03T16:21:40Z")
 Howard,  I was just trying something simple like this: `var worldOverlay = new WorldMapKitWmsWpfOverlay();                worldOverlay.IsVisible = true;                worldOverlay.DrawTilesProgressChanged += OnMapProgressChanged;                map.Overlays.Add("WMK", worldOverlay);`   If I step through the line where I set IsVisible, an exception is thrown.  Maybe I need DII. How do I get this?  I am still in eval mode till our purchase comes through. ---
**Author:** ![Raquibur](https://community.thinkgeo.com/letter_avatar_proxy/v4/letter/r/a9adbd/32.png) [@Raquibur](https://community.thinkgeo.com/u/Raquibur)\ **Post date:** [August 3, 2010, 4:28pm UTC](https://community.thinkgeo.com/t/worldmapkitwmswpfoverlay-throws-null-exception-when-setting-isvisible/2763/4 "2010-08-03T16:28:55Z")
Dear Klaus,      I tested your code. It worked fine for me. I have been working with Map suite for a while. One think i noticed that, the exceptions are misleading.So, my suggestion is that you should check other part of the code and see if your application is generating exception else where.      Thanks      Raquib ---
**Author:** ![Raquibur](https://community.thinkgeo.com/letter_avatar_proxy/v4/letter/r/a9adbd/32.png) [@Raquibur](https://community.thinkgeo.com/u/Raquibur)\ **Post date:** [August 3, 2010, 4:29pm UTC](https://community.thinkgeo.com/t/worldmapkitwmswpfoverlay-throws-null-exception-when-setting-isvisible/2763/5 "2010-08-03T16:29:00Z")
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**Author:** ![Klaus3](https://community.thinkgeo.com/letter_avatar_proxy/v4/letter/k/e5b9ba/32.png) [@Klaus3](https://community.thinkgeo.com/u/Klaus3)\ **Post date:** [August 3, 2010, 9:14pm UTC](https://community.thinkgeo.com/t/worldmapkitwmswpfoverlay-throws-null-exception-when-setting-isvisible/2763/6 "2010-08-03T21:14:32Z")
Raquibur, no, it is definitely not my code.        i just modified the DisplayASimpleMap sample as follows:   `  private void WpfMap_Loaded(object sender, RoutedEventArgs e)        {            Map1.MapUnit = GeographyUnit.DecimalDegree;            Map1.CurrentExtent = new RectangleShape(-155.733, 95.60, 104.42, -81.9);             WorldMapKitWmsWpfOverlay worldOverlay = new WorldMapKitWmsWpfOverlay();            // Step over this line and a null reference exception is thrown.            // If i set IsVisible to false, however,exception is not thrown.            worldOverlay.IsVisible = true;            Map1.Overlays.Add("WMK", worldOverlay);            Map1.Refresh();        } `      That line throw an exception when IsVisible== true.   It could be my DLL versions. I am using 4.0.40. ---
**Author:** ![Raquibur1](https://community.thinkgeo.com/letter_avatar_proxy/v4/letter/r/a6a055/32.png) [@Raquibur1](https://community.thinkgeo.com/u/Raquibur1)\ **Post date:** [August 4, 2010, 12:05am UTC](https://community.thinkgeo.com/t/worldmapkitwmswpfoverlay-throws-null-exception-when-setting-isvisible/2763/7 "2010-08-04T00:05:56Z")
Dear Klaus,      I think you are right. I tried with DLL version 4.0.40 and i get the same issue.     ---
**Author:** ![Howard](https://community.thinkgeo.com/letter_avatar_proxy/v4/letter/h/90ced4/32.png) [@Howard](https://community.thinkgeo.com/u/Howard)\ **Post date:** [August 4, 2010, 1:24am UTC](https://community.thinkgeo.com/t/worldmapkitwmswpfoverlay-throws-null-exception-when-setting-isvisible/2763/8 "2010-08-04T01:24:53Z")
Hi Klaus, I think this is a bug in 4.0.40 which is fixed in the latest version. Now the latest build is 4.0.91.0, you can download the latest package everyday at: [helpdesk.thinkgeo.com](http://helpdesk.thinkgeo.com) Just let me know if you have more queries. Thanks, Howard ---
**Author:** ![Klaus3](https://community.thinkgeo.com/letter_avatar_proxy/v4/letter/k/e5b9ba/32.png) [@Klaus3](https://community.thinkgeo.com/u/Klaus3)\ **Post date:** [August 4, 2010, 10:03pm UTC](https://community.thinkgeo.com/t/worldmapkitwmswpfoverlay-throws-null-exception-when-setting-isvisible/2763/9 "2010-08-04T22:03:25Z")
That was it, thanks Howard. ---
**Author:** ![Howard](https://community.thinkgeo.com/letter_avatar_proxy/v4/letter/h/90ced4/32.png) [@Howard](https://community.thinkgeo.com/u/Howard)\ **Post date:** [August 6, 2010, 12:11am UTC](https://community.thinkgeo.com/t/worldmapkitwmswpfoverlay-throws-null-exception-when-setting-isvisible/2763/10 "2010-08-06T00:11:32Z")
Klaus,      You are welcome, just feel free to let us know if you have more queries.      Thanks,   Howard