Рисование в paintBox

public class DrawApp : System.Windows.Forms.Form
{
private PictureBox pictureBox1;
private bool flagDraw = false;
public DrawApp()
{
InitializeComponent();

}
private void InitializeComponent()
{
...
pictureBox1 = new PictureBox();
...
}

private void pictureBox1_MouseUp(...)
{
flagDraw = false;
}

private void pictureBox1_MouseDown(...)
{
flagDraw = true;
}


private void pictureBox1_MouseMove(..., MouseEventArgs e)
{
if(flagDraw == true)
{
Graphics g = Graphics.FromHwnd( pictureBox1.Handle);
SolidBrush brush = new SolidBrush(Color.Red);
g.FillEllipse(brush, e.X, e.Y, 10, 10);
}
}
                       
}