using ESRI.ArcGIS.Display;

using ESRI.ArcGIS.DisplayUI

private esriTOCControlItem toccItem = esriTOCControlItem.esriTOCControlItemNone;

        private ILayer iLayer = null;

        private IBasicMap iBasicMap = null;

        private void axTOCControl1_OnDoubleClick(object sender, ITOCControlEvents_OnDoubleClickEvent e)

        {

            object unk = null;

            object data = null;

            if (e.button == )

            {

                axTOCControl1.HitTest(e.x, e.y, ref toccItem, ref iBasicMap, ref iLayer, ref unk, ref data);

                System.Drawing.Point pos = new System.Drawing.Point(e.x, e.y);

                if (this.toccItem == esriTOCControlItem.esriTOCControlItemLegendClass)

                {

                    ESRI.ArcGIS.Carto.ILegendClass pLC = new LegendClassClass();

                    ESRI.ArcGIS.Carto.ILegendGroup pLG = new LegendGroupClass();

                    if (unk is ILegendGroup)

                    {

                        pLG = (ILegendGroup) unk;

                    }

                    pLC = pLG.get_Class((int) data);

                    ISymbol pSym;

                    pSym = pLC.Symbol;

                    ESRI.ArcGIS.DisplayUI.ISymbolSelector pSS = new ESRI.ArcGIS.DisplayUI.SymbolSelectorClass();

                    bool bOK = false;

                    pSS.AddSymbol(pSym);

                    bOK = pSS.SelectSymbol();

                    if (bOK)

                    {

                        pLC.Symbol = pSS.GetSymbolAt();

                    }

                    this.axMapControl1.ActiveView.Refresh();

                    this.axTOCControl1.Refresh();

                }

            }

        }