c#无法与其他表单中的列表框交互

Form2 form2 = new Form2();
form2.Show();

private void UpdateListBox(string item)
{
    if (listBox1.InvokeRequired)
    {
        listBox1.Invoke(new MethodInvoker(delegate { listBox1.Items.Add(item); }));
    }
    else
    {
        listBox1.Items.Add(item);
    }
}

public partial class Form1 : Form
{
    private Form2 form2;

    public Form1()
    {
        InitializeComponent();
        form2 = new Form2();
    }

    private void button1_Click(object sender, EventArgs e)
    {
        form2.UpdateListBox("New Item");
    }
}

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

    public void UpdateListBox(string item)
    {
        if (listBox1.InvokeRequired)
        {
            listBox1.Invoke(new MethodInvoker(delegate { listBox1.Items.Add(item); }));
        }
        else
        {
            listBox1.Items.Add(item);
        }
    }
}