Question

How can I open a form one time when I double click a dataGridView cell ?

private void dataGridView1_CellMouseDoubleClick(object sender, DataGridViewCellMouseEventArgs e)
{
    //string queryString = "SELECT id, thename, address,fax,mobile,email,website,notes FROM movie";
    int currentRow = int.Parse(e.RowIndex.ToString());
    try
    {
        string movieIDString = dataGridView1[0, currentRow].Value.ToString();
        movieIDInt = int.Parse(movieIDString);
    }
    catch (Exception ex) { }
    // edit button
    if (e.RowIndex != -1)
    {
        string id = dataGridView1[0, currentRow].Value.ToString();
        string thename = dataGridView1[1, currentRow].Value.ToString();
        string address = dataGridView1[2, currentRow].Value.ToString();
        string fax = dataGridView1[3, currentRow].Value.ToString();
        string mobile = dataGridView1[4, currentRow].Value.ToString();
        string email = dataGridView1[5, currentRow].Value.ToString();
        string website = dataGridView1[6, currentRow].Value.ToString();
        string notes = dataGridView1[7, currentRow].Value.ToString();

        Form4 f4 = new Form4();

        f4.id = movieIDInt;
        f4.thename = thename;
        f4.address = address;
        f4.fax = fax;
        f4.mobile = mobile;
        f4.email = email;
        f4.website = website;
        f4.notes = notes;


        f4.Show();
    }
}

this code opens a form each time I click a dataGridView, I want if it is opened, doubleClick will not open it again

Answer 1

Keep the opened form in a class field
e.g. instead of you code, call a method like this one:

    Form4 f4 = null; // class field

    // call this method when cellMouseDoubleClick is triggered
    private void OpenForm4IfNotOpened()
    {
        if (f4 == null || f4.IsDisposed)
        {
            f4 = new Form4();

            f4.id = movieIDInt;
            f4.thename = thename;
            f4.address = address;
            f4.fax = fax;
            f4.mobile = mobile;
            f4.email = email;
            f4.website = website;
            f4.notes = notes;
            f4.Show();
        }
        else
        {
            f4.BringToFront();
        }
    }