How to keep the form instance for further re-open?

I am using C# 2010. From my MdiParent toolstrip I am using the following codes to open the mdichild.

public partial class Form1 : Form
{
    Form3 MyNewName = New Form3();

    private void toolStripButton2_Click(object sender, EventArgs e)
    {
        //Form3 MyNewName = New Form3();
        MyNewName.MdiParent = this;
        MyNewName.FormBorderStyle = FormBorderStyle.No开发者_运维问答ne;
        MyNewName.Dock = DockStyle.Fill;
        MyNewName.Show();
    }
}

And for once the close button is clicked all of mdichildren use to close by its MDI_form closing event. But the problem is I cannot reopen the form it says "cannot access a disposed object". And if I use

Form3 MyNewName = New Form3();

then the other subs are not running...

So how to keep the instances permanently even if the form is closed?

Use Form.Hide instead of Form.Close.