Cannot re-open a form after it was closed

Question

I have a parent form (Main) and a child form (form1). The parent form's IsMdiContainer is set to true. When I click on a menu item, the child form is opened within the parent form, no problem. But when I close the child form and try to re-open it by clicking on the menu item again, it does not show, and there's an error: "Invisible or disabled control cannot be activated."

It appears that form1 is not really closed, it's just hidden somewhere but somehow I cannot re-display it. I tried both form1.Show() and form1.Visible = true but nothing works. Here's my code:

public partial class Main : Form
    {
        Form1 form1;
        public Main()
        {
            InitializeComponent();
        }

        private void form1ToolStripMenuItem_Click(object sender, EventArgs e)
        {

            if (form1 != null)
            {
                form1.Show();
                this.ActiveControl = form1;
                form1.WindowState = FormWindowState.Normal;
                form1.BringToFront();
                return;
            }
            else if (form1 == null || form1.IsDisposed)
            {
                form1 = new Form1();
                form1.MdiParent = this;
                form1.TopLevel = false;
                form1.Dock = DockStyle.Fill;
                form1.Show();
                this.ActiveControl = form1;
                form1.BringToFront();
            }
        }
    }

Henry Vuong · Answer

I found a workaround. I put this in form1: private void Form1_Load(object sender EventArgs e) { this.FormClosing += new FormClosingEventHandler(Form1_FormClosing); } private void Form1_FormClosing(object sender FormClosingEventArgs e) { this.Hide(); // hide the form instead of closing e.Cancel = true; // this cancels the close event. } This will hide form1 instead of closing it when user clicks the x icon at the top right corner of the form. I figure out the Show() method can only re-display a hidden form not a closed or disposed form.

Ryan Alford · Answer

personally I would have the code like this... public partial class Main : Form { public Main() { InitializeComponent(); } private void form1ToolStripMenuItem_Click(object sender EventArgs e) { Form1 form1 = new Form1(); form1.MdiParent = this; form1.TopLevel = false; form1.Dock = DockStyle.Fill; form1.Show(); this.ActiveControl = form1; form1.BringToFront(); } } then on your child form add the FormClosed Event private void Form1_FormClosed(object sender FormClosedEventArgs e) { this.Dispose(); }