Question

I have a multiple forms in my project. Form1 contains a pictureBox that displays a jpeg. In Form2 I have a trackBar that I would like to control the zoom level of the image in Form1. To keep it simple I only need 2 or 3 zoom levels. I’ve set the pictureBox to public in the Designer view. However, when I try to reference the pictureBox in Form2 it says it doesn’t exist. Below is the code I’m using to call Form2 in Form1

Form2 dataWindow = new Form2();
dataWindow.ShowDialog();

So in short the two things I need help with is:

1) Changing the properties of pictureBox1 from a separate form.
2) Creating a simple Zoom Formula.

Answer 1

1) Pass a form1 reference into form2’s constructor:

Form2 dataWindow = new Form2(this);
dataWindow.Show();

…

private form1 as Form1;
public Form2(Form1 frm1)
{
  form1 = frm1;
}

Then in Form2s TrackBar_Scroll event reference the PictureBox via the private member variable form1: form1.PictureBox1.Property

2) Magnify your pictures using a PictureBox so that you can zoom with the Mouse Wheel

---

The better way is events:

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }

    private void button1_Click(object sender, EventArgs e)
    {
        var form2 = new Form2();
        form2.TrackBarMoved += new Action<int>(ZoomPictureBox);
        form2.ShowDialog();
        form2.TrackBarMoved -= new Action<int>(ZoomPictureBox);

    }

    private void ZoomPictureBox(int zoomFactor)
    {
        pictureBox1.Width = 100 * zoomFactor;
        pictureBox1.Height = 100 * zoomFactor;
    }
}


public partial class Form2 : Form
{
    public Form2()
    {
        InitializeComponent();
    }

    public event Action<int> TrackBarMoved;

    private void trackBar1_Scroll(object sender, EventArgs e)
    {
        TrackBarMoved(trackBar1.Value);
    }
}