[c#] eraser command, reverible frame only showing but not to draw it

  public void MyMouseDown(Object sender, MouseEventArgs e)
        {
Graphics graphics = CreateGraphics();
int linh = System.Int32.Parse(textBox3.Text);

graphics.FillRectangle(new SolidBrush(Color.White), e.X, e.Y, linh, linh);

SelectRect.Width = 0;
SelectRect.Height = 0;
SelectRect.X = e.X;
SelectRect.Y = e.Y;

SelectRect.Width = linh;
SelectRect.Height = linh;
}


public void MyMouseMove(Object sender, MouseEventArgs e)
        {
Graphics graphics = CreateGraphics();
int linh = System.Int32.Parse(textBox3.Text);

graphics.FillRectangle(new SolidBrush(Color.White), e.X, e.Y,linh,linh);

SelectRect.Width = 0;
SelectRect.Height = 0;
SelectRect.X = e.X;
SelectRect.Y = e.Y;

SelectRect.Width = linh;
SelectRect.Height = linh;

Form thisform = (Form)sender;
ControlPaint.DrawReversibleFrame(thisform.RectangleToScreen(SelectRect), Color.Black, FrameStyle.Dashed);
}