Top-level control cannot be added to a control

Question

How to Load other Form inside panel in a primary form.

i was trying something like

private void frmInitialEntryBooks_Load(object sender, EventArgs e)
{
    frmSujbect objForm = new frmSujbect();
    pnl.Controls.Add(objForm);
    objForm.FormBorderStyle = System.Windows.Forms.FormBorderStyle.None;
    objForm.Dock = DockStyle.Fill;
    objForm.Show();
}

but it throw exception Top-level control cannot be added to a control at line pnl.Controls.Add(objForm);

You must use MDI. http://msdn.microsoft.com/en-us/library/xyhh2e7e(v=vs.110).aspx — Rotem, Jul 18 '14 at 09:26
http://msdn.microsoft.com/en-us/library/system.windows.forms.form.toplevel%28v=vs.110%29.aspx Just set toplevel to false? — sdf, Jul 18 '14 at 09:28
NO this is not MDI.... i want to display form inside a panel control — Nisar, Jul 18 '14 at 09:33

score 46 · Accepted Answer · edited Feb 21 '21 at 16:16

46

Use this:

private void frmInitialEntryBooks_Load(object sender, EventArgs e)
{
    frmSujbect objForm = new frmSujbect();
    objForm.TopLevel = false;
    pnl.Controls.Add(objForm);
    objForm.FormBorderStyle = System.Windows.Forms.FormBorderStyle.None;
    objForm.Dock = DockStyle.Fill;
    objForm.Show();
}

You are missing objForm.TopLevel = false;

edited Feb 21 '21 at 16:16

wonea

4,783
17
86
139

answered Jul 18 '14 at 09:35

Is there a way to set the opacity of the form that is inside the panel – F0r3v3r-A-N00b Jan 18 '17 at 05:46

score 4 · Answer 2 · edited Feb 21 '21 at 16:16

4

Set TopLevel = False in frmsubject then try

frmSujbect objForm = new frmSujbect();
pnl.Controls.Add(objForm);
objForm.Show();

edited Feb 21 '21 at 16:16

wonea

4,783
17
86
139

answered Jul 18 '14 at 09:33

Sathish

4,419
4
30
59

score 1 · Answer 3 · answered Mar 18 '20 at 08:05

I did the following:

Method:

private void PopulateFormIntoTab(Form form)
{
    TabPage page = tabControl1.SelectedTab;
    form.TopLevel = false;
    form.Parent = page;
    form.FormBorderStyle = FormBorderStyle.None;
    form.Dock = DockStyle.Fill;
    form.Show();

    tabControl1.TabPages[tabControl1.SelectedIndex].Controls.Clear();
    tabControl1.TabPages[tabControl1.SelectedIndex].Controls.Add(form);
}

Initialize the form:

public Form1()
{
    InitializeComponent();

    tabControl1.TabPages.Clear();
    tabControl1.Dock = DockStyle.Fill;
    tabControl1.TabPages.Add(new TabPage("Form2"));
    tabControl1.TabPages.Add(new TabPage("Form3"));
    tabControl1.TabPages.Add(new TabPage("Form4"));

    PopulateFormIntoTab(new Form2());
}

Finally, on selected tab index change:

private void TabControl1_SelectedIndexChanged(object sender, EventArgs e)
{
    Form form = null;

    switch (tabControl1.SelectedIndex)
    {
        case 1:
            form = new Form3();
            break;
        case 2:
            form = new Form4();
            break;
        default:
            form = new Form2();
            break;
    }

    PopulateFormIntoTab(form);
}

Top-level control cannot be added to a control

3 Answers3

Linked