Finding featureName in given XY mappoint in ArcMap using ArcObjects?

Question

I have new in ArcGis Dev. I am trying to create a tool. In the tool when cliked on the feature it will tell you about the XY point of the feature and the name of the feature. I am getting the XY. When I am trying to get the feature Name like if I click on Structure it will show the message "NE.Structure".

Apart structure, all the features I am getting null exception("System.NUllReferenceException occured in the dll but not handled by user code") and 2ndly what I tried is selecting the feature which I think is changing the map state. Can anyone please help. Here is what I tried

public override void OnMouseDown(int Button, int Shift, int X, int Y)
        {
            // TODO:  Add MapControl.OnMouseDown implementation
            screenPoint = new ESRI.ArcGIS.Geometry.Point();
            screenPoint.X = X;
            screenPoint.Y = Y;

            IScreenDisplay screenDisplay = (m_application.Document as IMxDocument).ActiveView.ScreenDisplay;

            mapPoint = screenDisplay.DisplayTransformation.ToMapPoint(X,Y);

            IMxDocument pMxDoc = (IMxDocument)m_application.Document;
            IMap pMap = (IMap)pMxDoc.FocusMap;
            mapPoint.SpatialReference = pMap.SpatialReference;

            IEnvelope env = new EnvelopeClass() as IEnvelope;
            // env.PutCoords(mapPoint.X, mapPoint.Y, mapPoint.X, mapPoint.Y);

            ITopologicalOperator pTopOp = mapPoint as ITopologicalOperator;

            ISpatialFilter pSpatFlt = new SpatialFilterClass();
            pSpatFlt.SpatialRel = esriSpatialRelEnum.esriSpatialRelIntersects;
            pSpatFlt.Geometry = pTopOp.Buffer(10);

            ESRI.ArcGIS.esriSystem.UID pFeatLayerUID = new ESRI.ArcGIS.esriSystem.UIDClass();
            pFeatLayerUID.Value = "{40A9E885-5533-11d0-98BE-00805F7CED21}"; /* refer http:// help.arcgis.com/EN/sdk/10.0/ArcObjects_NET/componenthelp/index.html#/Layers_Property/001200000m9t000000/ */
            IEnumLayer pEnumLayer = pMap.get_Layers(pFeatLayerUID, true);
            ILayer pThisLayer = pEnumLayer.Next();

            //IGeometry selectionGeometry = (mapPoint as ITopologicalOperator).Buffer(100); // make a buffer
            pMap.SelectByShape(mapPoint, (m_application as IMxApplication).SelectionEnvironment, false);

            IFeatureLayer pThisFeatLayer = pThisLayer as IFeatureLayer;

            IEnumFeature enumFeatures = (IEnumFeature)pMap.FeatureSelection;

            IFeature thisFeature = enumFeatures.Next();

            do
            {

                IGeometry thisGeom = thisFeature.ShapeCopy;

                   IFeatureCursor pFtCur = pThisFeatLayer.Search(pSpatFlt,true); 
                    IFeature pFt = pFtCur.NextFeature();

                    IFeatureClass fC = (IFeatureClass)pFt.Class;

                    MessageBox.Show(fC.AliasName.ToString());

                thisFeature = enumFeatures.Next();
            } while (thisFeature != null);  


            MessageBox.Show("X position is " + mapPoint.X.ToString() + "Y position is :" + mapPoint.Y.ToString());
        }
}

The exception I am getting is like :

This above error is coming in this line # IFeatureClass fC = (IFeatureClass)pFt.Class;

You asked me what I mean by changing the map state. In case user already selected any feature or an area, in that if my tool is trying to select the clicked feature, I am afraid it would deselect the user selection.

Answer 1

The issue is that you are not getting any features back from this line:

IFeature pFt = pFtCur.NextFeature();

The biggest issue is that you have a few things going on here and they are used together in a way that doesn't work. On one hand you are selecting features on the map and then looping through those features. On the other hand you are executing a spatial query on existing layers.

So I would pick one of the following methods depending on your needs.

The SelectByShape method:

public override void OnMouseDown(int Button, int Shift, int X, int Y)
{
    screenPoint = new ESRI.ArcGIS.Geometry.Point();
    screenPoint.X = X;
    screenPoint.Y = Y;

    IScreenDisplay screenDisplay = (m_application.Document as IMxDocument).ActiveView.ScreenDisplay;

    mapPoint = screenDisplay.DisplayTransformation.ToMapPoint(X,Y);

    IMxDocument pMxDoc = (IMxDocument)m_application.Document;
    IMap pMap = (IMap)pMxDoc.FocusMap;
    mapPoint.SpatialReference = pMap.SpatialReference;

    //IGeometry selectionGeometry = (mapPoint as ITopologicalOperator).Buffer(100); // make a buffer
    pMap.SelectByShape(mapPoint, (m_application as IMxApplication).SelectionEnvironment, false);

    IEnumFeature enumFeatures = (IEnumFeature)pMap.FeatureSelection;
    IFeature thisFeature;
    while((thisFeature = enumFeatures.Next()) != null)
    {
        IFeatureClass fC = (IFeatureClass)thisFeature.Class;

        MessageBox.Show(fC.AliasName.ToString());

        thisFeature = enumFeatures.Next();
    }   


    MessageBox.Show("X position is " + mapPoint.X.ToString() + "Y position is :" + mapPoint.Y.ToString());
}

The layer loop method:

public override void OnMouseDown(int Button, int Shift, int X, int Y)
{
    // TODO:  Add MapControl.OnMouseDown implementation
    screenPoint = new ESRI.ArcGIS.Geometry.Point();
    screenPoint.X = X;
    screenPoint.Y = Y;

    IScreenDisplay screenDisplay = (m_application.Document as IMxDocument).ActiveView.ScreenDisplay;

    mapPoint = screenDisplay.DisplayTransformation.ToMapPoint(X,Y);

    IMxDocument pMxDoc = (IMxDocument)m_application.Document;
    IMap pMap = (IMap)pMxDoc.FocusMap;
    mapPoint.SpatialReference = pMap.SpatialReference;

    ITopologicalOperator pTopOp = mapPoint as ITopologicalOperator;

    ISpatialFilter pSpatFlt = new SpatialFilterClass();
    pSpatFlt.SpatialRel = esriSpatialRelEnum.esriSpatialRelIntersects;
    pSpatFlt.Geometry = pTopOp.Buffer(10);

    ESRI.ArcGIS.esriSystem.UID pFeatLayerUID = new ESRI.ArcGIS.esriSystem.UIDClass();
    pFeatLayerUID.Value = "{40A9E885-5533-11d0-98BE-00805F7CED21}"; /* refer http:// help.arcgis.com/EN/sdk/10.0/ArcObjects_NET/componenthelp/index.html#/Layers_Property/001200000m9t000000/ */
    IEnumLayer pEnumLayer = pMap.get_Layers(pFeatLayerUID, true);

    ILayer pThisLayer;
    while((pThisLayer = pEnumLayer.Next()) != null)
    {
        IFeatureCursor pFtCur = pThisFeatLayer.Search(pSpatFlt,true); 
        IFeature pFt = pFtCur.NextFeature();

        if(pFt != null)
        {
            IFeatureClass fC = (IFeatureClass)pFt.Class;
            MessageBox.Show(fC.AliasName.ToString());
            break;
        }
    }   

    MessageBox.Show("X position is " + mapPoint.X.ToString() + "Y position is :" + mapPoint.Y.ToString());
}

I'm not able to test these at the moment, but it should get you started.