Add-in stops working with no apparent error

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06-09-2015 11:59 AM
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New Contributor III

I am developing a simple add-in that will trigger an action after user selects features on the map. The action will essentially make sure a dockable window is open and in that window display information about the selected features.

I have implemented a simple function that loops over selected features using IEnumFeature and collects their OIDs. To make sure the OIDs are present for all features in the selection, I set the IEnumFeatureSetup.AllFields = true.

Now to the problem. After I've selected a number features several times (regardless of what features or how many I select), the SelectionChanged event stops from being fired. It appears as if the add-in has crashed, but no error message is displayed. This happens both in debug and production. If I try to restart the add-in by de-selecting it in the Customise->Extensions menu, I can no longer select it back. However, ArcMap works fine otherwise. To make the add-in work again I must restart ArcMap.

I have done some naive memory usage inspection using Task Manager. Memory usage raises as I keep re-selecting features. Is this a memory leak? I am releasing the IEnum reference so this should, at least in theory, not be a problem.

The features are pulled from a file geodatabase. They have 5 short text fields each and there is around 1300 of them. The more features I select at once, the sooner the add-in stops working (e.g. if I select all of the features in the map at once, the SelectionChanged event won't be fired again).

I am developing in Arcobjects 10.1 SDK with Visual Studio 10 for C# Express using .NET 3.5. I cannot upgrade nor can I use .NET 4.0 due to client constraints. The add-in is being tested in ArcMap 10.1.

using System;

using System.Collections.Generic;

using System.Diagnostics;

using System.Text;

using System.IO;

using System.Collections;

using ESRI.ArcGIS.Framework;

using ESRI.ArcGIS.esriSystem;

using ESRI.ArcGIS.Carto;

using ESRI.ArcGIS.Desktop.AddIns;

using ESRI.ArcGIS.Geodatabase;

using ESRI.ArcGIS.Geometry;

using System.Runtime.InteropServices;

namespace DfT.Maritime.DeepPort {

    public class DeepPortExtension: ESRI.ArcGIS.Desktop.AddIns.Extension {

        private static IActiveViewEvents_Event ViewEvents {

            get { return ArcMap.Document.ActiveView as IActiveViewEvents_Event; }

        }

        public DeepPortExtension() {

        }

        protected override void OnStartup() {

        }

        protected override bool OnSetState(ExtensionState state) {

            Init();

            return base.OnSetState(state);

        }

        private void Init() {

            if (ArcMap.Document.ActiveView.IsActive()) {

                InitAddin();

            } else {

                ArcMap.Events.OpenDocument += delegate() {

                    InitAddin();

                };

                ArcMap.Events.NewDocument += delegate() {

                    InitAddin();

                };

            }

        }

        private void InitAddin() {

            // Bind selection changed handler

            ViewEvents.SelectionChanged += SelectionChanged_Handler;

        }

        private void SelectionChanged_Handler() {

            ISelection selection = ArcMap.Document.FocusMap.FeatureSelection;

            IEnumFeature featuresEnum = (IEnumFeature)selection;

            IEnumFeatureSetup featureSetup = (IEnumFeatureSetup)selection;

            featureSetup.AllFields = true;

            string message = "";

            IFeature feature;

            while ((feature = featuresEnum.Next()) != null) {

                int fldID = feature.Fields.FindField("locode");

                message += feature.get_Value(fldID).ToString() + ",";

            }

            System.Windows.Forms.MessageBox.Show(message);

            Marshal.ReleaseComObject(featuresEnum);

            Marshal.ReleaseComObject(featureSetup);

            Marshal.ReleaseComObject(selection);

        }

    }

}


Please help, this has been bugging me for the good part of the last week!

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New Contributor III

For what it's worth, here's how I solved the problem. Is seems it was the repeated call to ArcMap.Document.FocusMap.FeatureSelection that was breaking my add-in. If I instead store the focus map in a member variable IMap map and retrieve the feature selection by calling map.FeatureSelection is works just fine.

using System; 

using System.Collections.Generic; 

using System.Diagnostics; 

using System.Text; 

using System.IO; 

using System.Collections; 

using ESRI.ArcGIS.Framework; 

using ESRI.ArcGIS.esriSystem; 

using ESRI.ArcGIS.Carto; 

using ESRI.ArcGIS.Desktop.AddIns; 

using ESRI.ArcGIS.Geodatabase; 

using ESRI.ArcGIS.Geometry; 

using System.Runtime.InteropServices; 

 

namespace DfT.Maritime.DeepPort { 

 

    public class DeepPortExtension: ESRI.ArcGIS.Desktop.AddIns.Extension { 

 

        IMap map;

        private static IActiveViewEvents_Event ViewEvents { 

            get { return ArcMap.Document.ActiveView as IActiveViewEvents_Event; } 

        } 

 

        public DeepPortExtension() { 

        } 

 

        protected override void OnStartup() { 

        } 

 

        protected override bool OnSetState(ExtensionState state) { 

            Init(); 

            return base.OnSetState(state); 

        } 

 

        private void Init() { 

            if (ArcMap.Document.ActiveView.IsActive()) { 

                InitAddin(); 

            } else { 

                ArcMap.Events.OpenDocument += delegate() { 

                    InitAddin(); 

                }; 

                ArcMap.Events.NewDocument += delegate() { 

                    InitAddin(); 

                }; 

            } 

        } 

 

        private void InitAddin() { 

            // Bind selection changed handler 

            ViewEvents.SelectionChanged += SelectionChanged_Handler;

            //

            // Store focus map in a member variable!!!

            // 

            map = ArcMap.Document.FocusMap;

        } 

 

        private void SelectionChanged_Handler() { 

 

            //

            // Retrieve selected features from member variable!!!

            //

            ISelection selection = map.FeatureSelection; 

            IEnumFeature featuresEnum = (IEnumFeature)selection; 

            IEnumFeatureSetup featureSetup = (IEnumFeatureSetup)selection; 

 

            featureSetup.AllFields = true; 

 

            string message = ""; 

            IFeature feature; 

 

            while ((feature = featuresEnum.Next()) != null) { 

                int fldID = feature.Fields.FindField("locode"); 

                message += feature.get_Value(fldID).ToString() + ","; 

            } 

 

            System.Windows.Forms.MessageBox.Show(message); 

 

            Marshal.ReleaseComObject(featuresEnum); 

            Marshal.ReleaseComObject(featureSetup); 

            Marshal.ReleaseComObject(selection); 

        } 

    } 

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MVP Honored Contributor

Have you tried using Try..Catch in the SelectionChanged_Handler function to see if there is anything unusual happening?

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New Contributor III

Yes. I have tried to wrap the whole block of code in a try..catch to no avail. Catching Exception doesn't seem to help, unfortunately, as none seems to be thrown...

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MVP Honored Contributor

How about using FinalReleaseComObject or the Garbage Collector, as shown in this discussion?

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New Contributor III

All right, this bug is very odd. I have tried to force garbage collection but the only effect was that the SelectionChanged_Handler would get called only once upon selecting features. After that, the add-in would stop working as it does without the forced collection. I am no expert in using forced garbage collection, but this approach doesn't seem to be the answer to my problem and appears to be frowned upon by many C# programmes (that doesn't mean it's wrong, I know).

I have altered the code to localize the problem. It seems that the issue is caused by the growing message string, i.e. the step message += feature.HasOID.ToString() + "\n"; (line 15.)

The following code breaks as described previously:

private void SelectionChanged_Handler() {

    string message = "";

    try {

        ISelection selection = ArcMap.Document.FocusMap.FeatureSelection;

        IEnumFeature featuresEnum = (IEnumFeature)selection;

        IEnumFeatureSetup featureSetup = (IEnumFeatureSetup)selection;

        featureSetup.AllFields = true;

        IFeature feature;

        while ((feature = featuresEnum.Next()) != null) {

            message += feature.HasOID + ",";

            Marshal.FinalReleaseComObject(feature);

        }

        Marshal.FinalReleaseComObject(featuresEnum);

        Marshal.FinalReleaseComObject(featureSetup);

    } catch (Exception e) {

        System.Windows.Forms.MessageBox.Show(e.Message);

    }

    System.Windows.Forms.MessageBox.Show(message);

}

No exception is caught, no error displayed, the add-in simply stops showing the message as expected and cannot be re-initialized in the Customize menu.

However, the altered code below seems to run OK:

private void SelectionChanged_Handler() {

    List<string> message = new List<string>();

    try {

        ISelection selection = ArcMap.Document.FocusMap.FeatureSelection;

        IEnumFeature featuresEnum = (IEnumFeature)selection;

        IEnumFeatureSetup featureSetup = (IEnumFeatureSetup)selection;

        featureSetup.AllFields = true;

        IFeature feature;

        while ((feature = featuresEnum.Next()) != null) {

            message.Add(feature.HasOID.ToString());

            Marshal.FinalReleaseComObject(feature);

        }

        Marshal.FinalReleaseComObject(featuresEnum);

        Marshal.FinalReleaseComObject(featureSetup);

    } catch (Exception e) {

        System.Windows.Forms.MessageBox.Show(e.Message);

    }

    System.Windows.Forms.MessageBox.Show(String.Join(",", message.ToArray()));

    message.Clear();

}

Can someone explain what's going on behind the scene in these two cases?

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Highlighted
New Contributor III

For what it's worth, here's how I solved the problem. Is seems it was the repeated call to ArcMap.Document.FocusMap.FeatureSelection that was breaking my add-in. If I instead store the focus map in a member variable IMap map and retrieve the feature selection by calling map.FeatureSelection is works just fine.

using System; 

using System.Collections.Generic; 

using System.Diagnostics; 

using System.Text; 

using System.IO; 

using System.Collections; 

using ESRI.ArcGIS.Framework; 

using ESRI.ArcGIS.esriSystem; 

using ESRI.ArcGIS.Carto; 

using ESRI.ArcGIS.Desktop.AddIns; 

using ESRI.ArcGIS.Geodatabase; 

using ESRI.ArcGIS.Geometry; 

using System.Runtime.InteropServices; 

 

namespace DfT.Maritime.DeepPort { 

 

    public class DeepPortExtension: ESRI.ArcGIS.Desktop.AddIns.Extension { 

 

        IMap map;

        private static IActiveViewEvents_Event ViewEvents { 

            get { return ArcMap.Document.ActiveView as IActiveViewEvents_Event; } 

        } 

 

        public DeepPortExtension() { 

        } 

 

        protected override void OnStartup() { 

        } 

 

        protected override bool OnSetState(ExtensionState state) { 

            Init(); 

            return base.OnSetState(state); 

        } 

 

        private void Init() { 

            if (ArcMap.Document.ActiveView.IsActive()) { 

                InitAddin(); 

            } else { 

                ArcMap.Events.OpenDocument += delegate() { 

                    InitAddin(); 

                }; 

                ArcMap.Events.NewDocument += delegate() { 

                    InitAddin(); 

                }; 

            } 

        } 

 

        private void InitAddin() { 

            // Bind selection changed handler 

            ViewEvents.SelectionChanged += SelectionChanged_Handler;

            //

            // Store focus map in a member variable!!!

            // 

            map = ArcMap.Document.FocusMap;

        } 

 

        private void SelectionChanged_Handler() { 

 

            //

            // Retrieve selected features from member variable!!!

            //

            ISelection selection = map.FeatureSelection; 

            IEnumFeature featuresEnum = (IEnumFeature)selection; 

            IEnumFeatureSetup featureSetup = (IEnumFeatureSetup)selection; 

 

            featureSetup.AllFields = true; 

 

            string message = ""; 

            IFeature feature; 

 

            while ((feature = featuresEnum.Next()) != null) { 

                int fldID = feature.Fields.FindField("locode"); 

                message += feature.get_Value(fldID).ToString() + ","; 

            } 

 

            System.Windows.Forms.MessageBox.Show(message); 

 

            Marshal.ReleaseComObject(featuresEnum); 

            Marshal.ReleaseComObject(featureSetup); 

            Marshal.ReleaseComObject(selection); 

        } 

    } 

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