C#

namespace DoubleBufferPanelNameSpace
{
    public class DoubleBufferPanel : Panel
    {
        public DoubleBufferPanel()
        {
            this.SetStyle(ControlStyles.AllPaintingInWmPaint |
                          ControlStyles.UserPaint |
                          ControlStyles.DoubleBuffer |
                          ControlStyles.ResizeRedraw,
                          true);
            this.UpdateStyles();
        }
    }
}

private void doubleBufferPanel1_Paint(object sender, PaintEventArgs e)
{
    e.Graphics.DrawLine(new Pen(Brushes.Black), 0, 0, 10, 10);
}

public class DoubleBufferPanel : Panel 
{ 
    public DoubleBufferPanel() 
    { 
        this.SetStyle(
            ControlStyles.AllPaintingInWmPaint |
            ControlStyles.UserPaint |
            ControlStyles.DoubleBuffer |
            ControlStyles.ResizeRedraw, true);
        this.UpdateStyles();
    }

    protected override void OnPaint(PaintEventArgs e)
    {
        base.OnPaint(e);
        using (Pen pen = new Pen(Color.Black))
        {
            e.Graphics.DrawLine(pen, 0, 0, 10, 10);
        }
    }
}

Swetha Srinivasan wrote:

i want to check if the file is already open or not

MessageBox.Show(((Button)sender).Name + " Who raised this event?");

Button b = sender as Button;
if (b != null)
   {
   MessageBox.Show(b.Name + " Who raised this event?");
   }

if (sender is Button)
{
    Button button = sender as Button;
    // ...
}