title: (c# + windows forms) Adding items to listBox in different class
body: <p>I have two classes(forms), and I would like an item from <code>class2</code> to be added to <code>listBox</code> in <code>class1</code> when I click "Accept" button.</p>
  
  <p>I tried with the following code, but nothing changes in the listBox:</p>
  
  <pre><code>private void button1_Click(object sender, EventArgs e)
  {
      CarRental i = new CarRental();
      string id = idRental.Text.ToString();
  
      i.listBox1.Items.Add(id);
      i.listBox1.Update();
      this.Close();
  }
  </code></pre>
  
  <p>Where did I make the mistake?</p>