C#

protected override void OnMouseDown(MouseEventArgs e)<br />
{<br />
try<br />
{<br />
	Point downPoint = new Point(e.X,e.Y);<br />
	DataGrid.HitTestInfo hitInfo = this.HitTest(downPoint);<br />
	switch(hitInfo.Type)<br />
	{<br />
	case DataGrid.HitTestType.ColumnResize:<br />
            break;<br />
	default:<br />
	     base.OnMouseDown(e);<br />
	     break;<br />
	}<br />
}<br />
catch(Exception ex)<br />
{<br />
        Console.WriteLine(ex);<br />
}<br />
}

public class MicrosocDataGrid : DataGrid
{
    public MicrosocDataGrid ()
    {
    }

    public new event MouseEventHandler MouseDown; // shadowed, to trigger the events
         public new event MouseEventHandler MouseMove;

    protected override void OnMouseMove(MouseEventArgs e)
    {
        if (IsColumnResize(e.X, e.Y))
        {
            if (MouseMove != null)//the purpose of the shadowing, to trigger this event
            {
                 MouseMove(this, e);
            }
        }
        else
        {
            base.OnMouseMove(e);
        }
    }

    protected override void OnMouseDown(MouseEventArgs e)
    {
        if (IsColumnResize(e.X, e.Y))
        {
            if (MouseDown != null) //the purpose of the shadowing, to trigger this event
            {
                MouseDown(this, e);
            }
        }
        else
        {
            base.OnMouseDown(e);
        }
    }

    private bool IsColumnResize (int nX, int nY)
    {
        DataGrid.HitTestInfo hti = HitTest(nX, nY);
        return (hti.Type == DataGrid.HitTestType.ColumnResize);
    }
}

public class Form2 : Form
{
    public TextBox textBox1;
}

public class Form1 : Form
{
    public TextBox textBox1;
    // ...
    {
        ///...
        Form2 f = new Form2(); //this is just a sample. You may need to get the instance of Form2 that is active here.
        f.textBox1.Text=this.textBox1.Text;
    }
}