Cannot re-open a form after it was closed

Henry Vuong

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();
            }
        }
    }

2 Replies

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Henry Vuong18y ago
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 Alford18y ago
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();
}