Using custom event to draw shapes in another form c#

Question

I have 2 forms, Main Form & ModalBox.

In Main Form I have a button that when clicked draws a shape depending on the selected index of the comboBox.

// Create Rectangle or Ellipse 
  public void buttonAdd_Click(object sender, EventArgs e)
    {
        SolidBrush sb = new SolidBrush(Color.Red);

        Graphics g = panel1.CreateGraphics();

        if (shapeSizeControl1.comboBoxShapeSelection.SelectedIndex == 0)
        {
            g.FillRectangle(sb, Convert.ToSingle(shape.X), Convert.ToSingle(shape.Y), Convert.ToSingle(shape.Width), Convert.ToSingle(shape.Height));
        }
        else if (shapeSizeControl1.comboBoxShapeSelection.SelectedIndex == 1)
        {
            g.FillEllipse(sb, Convert.ToSingle(shape.X), Convert.ToSingle(shape.Y), Convert.ToSingle(shape.Width), Convert.ToSingle(shape.Height));
        }
    }

In the ModalBox form I have an Ok button which should do the same thing as the button in Main Form but it doesn't because I have no idea how to program it to do so.

What i've tried..

1. Copying the same code from Main Form buttonAdd_Click into ModalBox buttonOk_Click. Bad idea because I have to instantiate a new Main form to get the panel1 variable. If I do that nothing happens. Why? I'm not sure an explanation would be great.

2. Creating a custom event so when the ModalBox Form opens, once I press the ok button since its subscribed It will draw the shape. 1 problem I have no idea where to call the event and check for null because the button is on the second form so If I call the custom event in the first form I have no where to call the event and do null check.

Goal

My goal is to figure out how to add shapes in the Main Form from the ModalBox Form using the Ok button in the ModalBox Form.

Answer 1

Just create a method DrawShape() in the main form that draws your shapes and call it from the button click.

// Main Form
private void button1_Click(object sender, EventArgs e)
{
    DrawShape();
}

Now create the modal form and set the owner

// Main form
private void button2_Click(object sender, EventArgs e)
{
    var dlg = new ModalBox();

    if (dlg.ShowDialog(this)==DialogResult.OK)
    {
        // do things
    }
}

Finally in the modal form call the DrawShape() function

// Modal form
private void button1_Click(object sender, EventArgs e)
{
    var parent = this.Owner as MainForm;
    parent.DrawShape();
}