C#

public override void Test(int arg) {
    using (Form f=new Form()) {
        f.Text="my latest form";
        f.Show();
        listForms("Form shown");
        f.Hide();
        listForms("Form hidden");
        // f.Close();                     // optional
        // listForms("Form closed");      //
    }
    GC.Collect();
    listForms("Collected");
}

private void listForms(string title) {
    log("List of forms: "+title);
    int i=0;
    foreach (Form f in Application.OpenForms) {
        log("    Form "+i+" text="+f.Text);
        i++;
    }
    log("Found "+i+" forms");
}

Roger Wright wrote:

an article that explained that if Close() is called on a hidden Form, it doesn't work, nor does it emit an error. At least, not reliably

DateTime t1;//to store the first time click
private void button1_Click(object sender, EventArgs e)
{
    if (t1.ToBinary() == 0)//first click
    {
        t1 = DateTime.Now;//set first click time
        label1.Text = "Hi";//what you do in click
    }
    else if (t1.AddMilliseconds(1000).CompareTo(DateTime.Now) > 0)//you can set the timespan in the number "1000"
    {

        label1.Text = "Hello";//what you do in DoubleClick
        t1 = DateTime.MinValue;//initial time variable
    }
    else//the second click time is out of the range
    {
        t1 = DateTime.MinValue;//initial time variable

    }
}