Custom UI elements using add-ins
AddGraphicsTool.cs
// Copyright 2012 ESRI
// 
// All rights reserved under the copyright laws of the United States
// and applicable international laws, treaties, and conventions.
// 
// You may freely redistribute and use this sample code, with or
// without modification, provided you include the original copyright
// notice and use restrictions.
// 
// See the use restrictions.
// 

using System;
using System.Collections.Generic;
using System.Text;
using System.IO;
using ESRI.ArcGIS.ArcMapUI;
using ESRI.ArcGIS.Framework;
using ESRI.ArcGIS.Geodatabase;
using ESRI.ArcGIS.SystemUI;
using ESRI.ArcGIS.Display;
using ESRI.ArcGIS.Carto;
using ESRI.ArcGIS.Geometry;

namespace CustomUIElements
{
  public class AddGraphicsTool : ESRI.ArcGIS.Desktop.AddIns.Tool
  {
    public AddGraphicsTool()
    {
    }

    protected override void OnUpdate()
    {
      Enabled = ArcMap.Application != null;
    }

    protected override void OnMouseDown(MouseEventArgs arg)
    {
      //Get the active view from the AecMap static class
      IActiveView activeView = ArcMap.Document.ActiveView;

      //if polyline object then get from the user's mouse clicks.
      IPolyline polyline = GetPolylineFromMouseClicks(activeView);

      //Make a color to draw the polyline. 
      IRgbColor rgbColor = new RgbColorClass();
      rgbColor.Red = 255;     

      //Add the user's drawn graphics as persistent on the map.
      AddGraphicToMap(activeView.FocusMap, polyline, rgbColor, rgbColor);

      //Best practice: Only redraw the portion of the active view that contains graphics. 
      activeView.PartialRefresh(esriViewDrawPhase.esriViewGraphics, null, null);
    }

    #region "Add Graphic to Map"

    ///<summary>Draw a specified graphic on the map using the supplied colors.</summary>
    ///      
    ///<param name="map">An IMap interface.</param>
    ///<param name="geometry">An IGeometry interface. It can be of the geometry type: esriGeometryPoint, esriGeometryPolyline, or esriGeometryPolygon.</param>
    ///<param name="rgbColor">An IRgbColor interface. The color to draw the geometry.</param>
    ///<param name="outlineRgbColor">An IRgbColor interface. For those geometry's with an outline it will be this color.</param>
    ///      
    ///<remarks>Calling this function will not automatically make the graphics appear in the map area. Refresh the map area after calling this function with Methods like IActiveView.Refresh or IActiveView.PartialRefresh.</remarks>
    public void AddGraphicToMap(IMap map, IGeometry geometry, IRgbColor rgbColor, IRgbColor outlineRgbColor)
    {
      IGraphicsContainer graphicsContainer = (IGraphicsContainer)map; // Explicit Cast
      IElement element = null;
      if ((geometry.GeometryType) == esriGeometryType.esriGeometryPoint)
      {
        // Marker symbols
        ISimpleMarkerSymbol simpleMarkerSymbol = new SimpleMarkerSymbolClass();
        simpleMarkerSymbol.Color = rgbColor;
        simpleMarkerSymbol.Outline = true;
        simpleMarkerSymbol.OutlineColor = outlineRgbColor;
        simpleMarkerSymbol.Size = 15;
        simpleMarkerSymbol.Style = esriSimpleMarkerStyle.esriSMSCircle;

        IMarkerElement markerElement = new MarkerElementClass();
        markerElement.Symbol = simpleMarkerSymbol;
        element = (IElement)markerElement; // Explicit Cast
      }
      else if ((geometry.GeometryType) == esriGeometryType.esriGeometryPolyline)
      {
        //  Line elements
        ISimpleLineSymbol simpleLineSymbol = new SimpleLineSymbolClass();
        simpleLineSymbol.Color = rgbColor;
        simpleLineSymbol.Style = esriSimpleLineStyle.esriSLSSolid;
        simpleLineSymbol.Width = 5;

        ILineElement lineElement = new LineElementClass();
        lineElement.Symbol = simpleLineSymbol;
        element = (IElement)lineElement; // Explicit Cast
      }
      else if ((geometry.GeometryType) == esriGeometryType.esriGeometryPolygon)
      {
        // Polygon elements
        ISimpleFillSymbol simpleFillSymbol = new SimpleFillSymbolClass();
        simpleFillSymbol.Color = rgbColor;
        simpleFillSymbol.Style = esriSimpleFillStyle.esriSFSForwardDiagonal;
        IFillShapeElement fillShapeElement = new PolygonElementClass();
        fillShapeElement.Symbol = simpleFillSymbol;
        element = (IElement)fillShapeElement; // Explicit Cast
      }
      if (!(element == null))
      {
        element.Geometry = geometry;
        graphicsContainer.AddElement(element, 0);
      }
    }
    #endregion



    #region "Get Polyline From Mouse Clicks"

    ///<summary>
    ///Create a polyline geometry object using the RubberBand.TrackNew method when a user click the mouse on the map control. 
    ///</summary>
    ///<param name="activeView">An ESRI.ArcGIS.Carto.IActiveView interface that will user will interact with to draw a polyline.</param>
    ///<returns>An ESRI.ArcGIS.Geometry.IPolyline interface that is the polyline the user drew</returns>
    ///<remarks>Double click the left mouse button to end tracking the polyline.</remarks>
    public IPolyline GetPolylineFromMouseClicks(IActiveView activeView)
    {

      IScreenDisplay screenDisplay = activeView.ScreenDisplay;

      IRubberBand rubberBand = new RubberLineClass();
      IGeometry geometry = rubberBand.TrackNew(screenDisplay, null);
      IPolyline polyline = (IPolyline)geometry;
      return polyline;

    }
    #endregion
  }

}