[ArcObjects]How to identify on a map layer

▣ ArcObjects Interface
 - IIdentify

▣ Code Snippet

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

■ Identify on a map

public static void IdentifyMap(IMap focusMap, IPoint mapPoint) {
    if (focusMap.LayerCount == 0) return;

    ESRI.ArcGIS.esriSystem.UID uid = new UIDClass();
    uid.Value = "{6CA416B1-E160-11D2-9F4E-00C04F6BC78E}";

    IEnumLayer enumLayer = focusMap.get_Layers(uid, true);
    enumLayer.Reset();

    ILayer layer = enumLayer.Next();
    while (layer != null) {
        if (layer.Valid && layer.Visible) {
            IdentifyLayer(focusMap, layer, mapPoint);
        }
        layer = enumLayer.Next();
    }
}

■ Identify on a layer

static void IdentifyLayer(IMap focusMap, ILayer layer, IPoint mapPoint) {
    bool isFeatureLayer = layer is IFeatureLayer;

    IIdentify identify = (IIdentify)layer;
    IGeometry searchGeometry = mapPoint;

    if (isFeatureLayer) {
        IFeatureLayer featureLayer = (IFeatureLayer)layer;
        if (featureLayer.FeatureClass.ShapeType != esriGeometryType.esriGeometryPolygon) {
            ITopologicalOperator topoOpt = (ITopologicalOperator)mapPoint;
            double radius = PixelsToMapUnits((IActiveView)focusMap, 6d);

            searchGeometry = topoOpt.Buffer(radius);
        }
    }

    ESRI.ArcGIS.esriSystem.IArray idArray = identify.Identify(searchGeometry);
    if (idArray == null) {
        return;
    }

    IActiveView activeView = (IActiveView)focusMap;

    for (int k = 0; k < idArray.Count; k++) {
        IIdentifyObj identifyObj = (IIdentifyObj)idArray.get_Element(k);

        if (isFeatureLayer) {
            IFeatureIdentifyObj featureObj = (IFeatureIdentifyObj)identifyObj;
            IRowIdentifyObject rowObj = (IRowIdentifyObject)featureObj;
            IFeature feature = (IFeature)rowObj.Row;

            // flash shape
            identifyObj.Flash(activeView.ScreenDisplay);

            // show attributes
            string infoMsg = string.Format("{0}'s OID = {1}", layer.Name, feature.OID);
            System.Windows.Forms.MessageBox.Show(infoMsg);
        } else {
            IRasterIdentifyObj rasterObj = (IRasterIdentifyObj)identifyObj;

            // show attributes
            string infoMsg = string.Format("{0}'s pixel value = {1}", layer.Name, rasterObj.Name);
            System.Windows.Forms.MessageBox.Show(infoMsg);
        }
    }
}

■ Convert screen pixels to map units

static double PixelsToMapUnits(IActiveView activeView, double pixelUnits) {
    IDisplayTransformation displayTrans = activeView.ScreenDisplay.DisplayTransformation;
    tagRECT deviceRECT = displayTrans.get_DeviceFrame();
    int pixelExtent = deviceRECT.right - deviceRECT.left;

    double realWorldDisplayExtent = displayTrans.VisibleBounds.Width;
    double sizeOfOnePixel = realWorldDisplayExtent / pixelExtent;

    return pixelUnits * sizeOfOnePixel;
}