Getting feature at point in C#

Question

I want to get the feature at where mouse was clicked in map. So I was wondering how to get features which intersects with that point. Plus I was wondering how can I check what type of object it is (point, poly-line, polygon) ?

Answer 1

To select from the map using the current selection environment (you can turn off selectability and visibility of layers then this wont pick them up.

Firstly you need to be creating a tool:

using ESRI.ArcGIS.Carto;
using ESRI.ArcGIS.ArcMapUI;
using ESRI.ArcGIS.Geometry;
using ESRI.ArcGIS.Framework;
using ESRI.ArcGIS.esriSystem;
using ESRI.ArcGIS.Display;
using ESRI.ArcGIS.Geodatabase;

namespace RED
{
    public class REd : ESRI.ArcGIS.Desktop.AddIns.Tool

Then in the OnMouseDown event of the tool:

protected override void OnMouseDown(MouseEventArgs arg)
{
    //if (arg.Button == System.Windows.Forms.MouseButtons.Left) // check for left mouse button if you like
    // convert point from 'screen' to 'map' coordinates
    IPoint MouseMapPoint = (ArcMap.Document.FocusMap as IActiveView).ScreenDisplay.DisplayTransformation.ToMapPoint(arg.X, arg.Y);
    // clear selection first
    ArcMap.Document.FocusMap.ClearSelection();
    // Select using the shape (point) to
    // select the feature(s) - false to select any intersecting, true to select just the first
    ArcMap.Document.FocusMap.SelectByShape(MouseMapPoint,(ArcMap.Application as IMxApplication).SelectionEnvironment,false);
    // get the (now) selected features
    IEnumFeature EnumFeatures = (IEnumFeature)ArcMap.Document.FocusMap.FeatureSelection;
    IFeature ThisFeature = EnumFeatures.Next();
    do
    {
        // get the geometry
        IGeometry ThisGeom = ThisFeature.ShapeCopy; // IMPORTANT! USE SHAPECOPY not SHAPE
        // do something different for each geometry type
        if (ThisGeom.GeometryType == esriGeometryType.esriGeometryPoint)
        { 
            // something for points (note: does not include multipoint)
        }
        else if (ThisGeom.GeometryType == esriGeometryType.esriGeometryPolygon)
        { 
            // something for polygons
        }
        else if (ThisGeom.GeometryType == esriGeometryType.esriGeometryPolyline)
        { 
            // something for polylines (note: polylines are different to lines)
        }
        else
        { 
            // unrecognized geometry type
        }
        ThisFeature = EnumFeatures.Next();
    } while (ThisFeature != null);  
}

Which works fine for selecting using a point... this will have problems when trying to select a point or line so to counter that use an increased search buffer (polygon) to make the selection:

// to increase the search

    IGeometry selectionGeometry = (MouseMapPoint as ITopologicalOperator).Buffer(SmallDistance); // make a buffer
    ArcMap.Document.FocusMap.SelectByShape(selectionGeometry, (ArcMap.Application as IMxApplication).SelectionEnvironment, false);

Read about IMap.SelectByShape, IEnumFeature, ITopologicalOperator and Esri Geometry Type Constants

Normally I don't do it that way - the selection environment gets in the way so I use IMap.Layers to iterate through each layer then with an ISpatialFilter make a selection against each layer... that works even if the layer is invisible and/or not selectable.