MDI Form detecting with a child form is added or removed

Question

Is there an event I can use to tell if a child form has been added or removed from the MDI parent?

Answer 1

Yes. On your main MDI form, wire up to the MdiChildActivated Event.

Like so:

public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            this.MdiChildActivate += new EventHandler(Form1_MdiChildActivate);
        }

        void Form1_MdiChildActivate(object sender, EventArgs e)
        {
            MessageBox.Show("Activated");
        }

        private void addToolStripMenuItem_Click(object sender, EventArgs e)
        {
            Form form2 = new Form2();
            form2.MdiParent = this;
            form2.Show();
        }
    }

And that event will fire when the child form is both activated or deactivated.

Answer 2

No, there is not. You would have to subclass Form and expose specific events that would indicate when the child is added and then route all attachments of child forms through a method that would wire up the child form, as well as raise the event.

Answer 3

Wire up the MdiChildActivate event and keep a list of recognized children. When a new form is activated, also wire up the FormClosed event.

private List<Form> ChildFormList = new List<Form>();

private void MyForm_MdiChildActivate(object sender, EventArgs e)
{
    Form f = this.ActiveMdiChild;

    if (f == null)
    {
        //the last child form was just closed
        return;
    }

    if (!ChildFormList.Contains(f))
    {
        //a new child form was created
        ChildFormList.Add(f);
        f.FormClosed += new FormClosedEventHandler(ChildFormClosed);
    }
    else
    {
        //activated existing form
    }
}

private void ChildFormClosed(object sender, FormClosedEventArgs e)
{
    //a child form was closed
    Form f = (Form)sender;
    ChildFormList.Remove(f);
}