Winforms c# Changing background Image of Parent form from popup form

Question

I have two forms a & b. Form a is main form and on one of its button click event form b is shown as a small window. On the popup (form b), I have an option to select image. What I need to do is when I click on save button of popup (form b), form a (main form's) background image should be set to image selected via popup form (b).

I have tried following code but this.Parent, this.Owner all is returning null for popup form (b). I have specified form a as MDI.

this.Owner.BackgroundImage = pictureBoxBackground.Image;
this.Parent.BackgroundImage = pictureBoxBackground.Image;

Answer 1

What I would do is have a public Image property like so inside Form b:

private Image image;
public Image SelectedImage
{
    get
    {
        return image;
    }
}

And then I would add a button_Click event (or whatever you use to confirm selection). This event would close the form and set the return image.

private void Button_Click(object sender, EventArgs e)
{
    image = [Whatever Image variable that you want to return];
    Close();
}

Making FormB look like this.

public class FormB : Form
{
    //[...]Stuff
    private Image image;
    public Image SelectedImage
    {
        get
        {
            return image;
        }
    }
    private void Button_Click(object sender, EventArgs e)
    {
        image = [Whatever Image variable that you want to return];
        Close();
    }
}

And finally, to use this for the background image of FormA. Simply have the following procedure.

public void ChangeBackground()
{
    FormB b = new FormB();
    b.ShowDialog();
    this.BackgroundImage = b.SelectedImage;
}