private void button1_Click(object sender, EventArgs e)
{
var form = Application.OpenForms.OfType <AddForm>().FirstOrDefault();
if (form != null)
{
form.Activate();
}
else
{
form = new AddForm();
form.Show();
}
}
private void addButton_Click(object sender, EventArgs e)
{
AddForm addForm = new AddForm();
addForm.Show();
}