//----------this is msinform code.When i click on symbology button symbology form get called--------------------------
Here I have used usercontrol themview1 which  stores the added layers with index selectorder.

      
    

 private void symbology_Click(object sender, EventArgs e)
        {
           
            if (symbology_btn.Checked == false)
            {
                if (selectedOrder == -1)
                    MessageBox.Show("First Select appropriate Layer");
                else
                {

                    Symbology symb = new Symbology();
                    symbology_btn.Checked = true;
                    filename = themeview1.Items[selectedOrder].ShapeName;   //storing layername in string filename
                  
                    symb.symblist = filename;
                    symb.MdiParent = this;
                    symb.Parent = winformsMap1;
                    
                    try
                    {
                        symb.Show();
                    }
                    catch (ObjectDisposedException od)
                    {
                        MessageBox.Show("Disposed Error..");

                    }
                }

            }
            else
            {
               symbology_btn.Checked =false;
                

            }
        }

//------------------This is code for symbology form---------------------------------------
//here i am inheriting mainform i.e. mdi form and passing shapefile name to txt_layer.text.
namespace WindowsFormsApplication2
{
    public partial class Symbology : Form
    {
        private string symlayer;
       
        private string layer;
        private string layername; 
        private string filename;
        private Collection<FeatureSourceColumn> file;
        private int index;
       
        private int countfield;
      
       
        ZedGraphStyle zedGraphStyle = new ZedGraphStyle();
        LayerOverlay layerOverlay2 = new LayerOverlay();
      
       
        public string symblist
        {
            get { return symlayer; }
            set { txt_layer.Text = value; }

        }

       
        public Symbology()
        {
            InitializeComponent();
        }

       
       
        private void zedGraphStyle_BarGraphDrawing(object sender, ZedGraphDrawingEventArgs e)
        {
           
            WinformsMap winformsMap1 = (WinformsMap)this.Parent;
            double scale = ExtentHelper.GetScale(winformsMap1.CurrentExtent, winformsMap1.Width, GeographyUnit.DecimalDegree);

            // Change the size of the graph based on the scale.  It will get bigger as you zoom in.
            int graphHeight = Convert.ToInt32(700000000 / scale);

            ZedGraphControl zedGraph = new ZedGraphControl();
            zedGraph.Size = new Size(graphHeight, graphHeight);

            GraphPane myPane = zedGraph.GraphPane;
            
            for (index = 0; index < countfield; index++)
            {
                myPane.XAxis.Title.Text = list_fieldfinal.Items[index].ToString();
                myPane.YAxis.Title.Text = list_fieldfinal.Items[index].ToString();
            }

            PointPairList list = new PointPairList();
            Random rand = new Random();

            for (index = 0; index < countfield; index++)
            {
                try
                {

                    string fields = list_fieldfinal.Items[index].ToString();
                    list.Add(index + 1, double.Parse(e.Feature.ColumnValues[fields]));
                }
                catch (FormatException formatexception)
                {
                    //MessageBox.Show("Please Check the Datatype of attribute.");

                }
                finally
                {
                    
                }
            }

            string name = " Bar";
            BarItem myCurve = myPane.AddBar(name, list, Color.Blue);
           
            zedGraph.AxisChange();
            e.Bitmap = zedGraph.GraphPane.GetImage();
        }

        public void bargraph()
        {

            layer = txt_layer.Text;
            WinformsMap winformsMap1 = (WinformsMap)this.Parent;

            countfield = list_fieldfinal.Items.Count;
           
                if (countfield == 2)
                {
                    layername = new FileInfo(layer).Name;

                    ShapeFileFeatureLayer layerfile = new ShapeFileFeatureLayer(layername);

                    
                    InMemoryFeatureLayer bargraphLayer = (InMemoryFeatureLayer)winformsMap1.FindFeatureLayer(layer);

                   

                    bargraphLayer.ZoomLevelSet.ZoomLevel01.CustomStyles.Add(zedGraphStyle);
                    bargraphLayer.ZoomLevelSet.ZoomLevel01.ApplyUntilZoomLevel = ApplyUntilZoomLevel.Level20;

                    zedGraphStyle.ZedGraphDrawing += new EventHandler<ZedGraphDrawingEventArgs>(zedGraphStyle_BarGraphDrawing);

                    for (int count = 0; count < countfield; count++)
                    {
                        zedGraphStyle.RequiredColumnNames.Add(list_fieldfinal.Items[count].ToString());
                    }

                     layerOverlay2.Layers.Add("BargraphsLayer", bargraphLayer);
                    winformsMap1.Overlays.Add("BargraphOverlay", layerOverlay2);

                  
                    winformsMap1.Refresh();
                }
                else
                    MessageBox.Show("Two Items should be compulsory For Bar graph operation");


        }

        
       
   
       
    }
}