mdichild form does not show

Question

I have a bunch of mdichild forms already designed and would Like to show the forms as a mdichild. I set the main form to mdi and I am able to show one of the forms as a mdichild correctly. The code that is giving me a hassle is:

    public partial class KeyboardSettingsForm : Form
    {
        private mainForm _mForm;

        public KeyboardSettingsForm()
        {
            InitializeComponent();
            _mForm = new mainForm(); //<---mdiparent
            this.MdiParent = _mForm; //<---Commenting out this line shows the form

            this.Shown += new System.EventHandler(this.KeyboardSettingsForm_Shown);

        }
    }

I am not sure why if I comment out: this.MdiParent = _mForm; the form will show(but not as a mdichild). Leaving that code intact, the form refuses to show. How do I get that form to show as a mdichild?

Updated Working Code

public partial class mainForm : Form
{
    private NavigationForm _navForm;
    public mainForm()
    {
        InitializeComponent();


        this.Shown += new System.EventHandler(this.mainForm_Shown);

    }

    private void mainForm_Shown(object sender, EventArgs e)
    {
        _navForm = new NavigationForm(this);
        _navForm.MdiParent = this;
        _navForm.Show();
    }

    private void mainForm_Load(object sender, EventArgs e)
    {

    }

}

public partial class NavigationForm : Form
{

    private KeyboardSettingsForm _wKeyboard;

    public NavigationForm(Form frm)
    {
        InitializeComponent();

        _wKeyboard = new KeyboardSettingsForm(frm);


    }

    private void NavigationForm_Load(object sender, EventArgs e)
    {

    }

    private void keyboardPictureBox_Click(object sender, EventArgs e)
    {
        _wKeyboard.Show();

    }

}

public partial class KeyboardSettingsForm : Form
{
    private Form _mdiParent;

    public KeyboardSettingsForm(Form frm)
    {
        InitializeComponent();
        _mdiParent = frm;
        this.MdiParent = frm;

        this.Shown += new System.EventHandler(this.KeyboardSettingsForm_Shown);

    }

    private void KeyboardSettingsForm_Load(object sender, EventArgs e)
    {
        MessageBox.Show(_mdiParent.Name);
    }

    private void KeyboardSettingsForm_Shown(object sender, EventArgs e)
    {

    }
}

Answer 1

you need to make mForm an mdi container:

mForm.IsMdiContainer = true;

Answer 2

You need to show Main Form explicitly as follows:

_mForm = new mainForm();
this.MdiParent = _mForm;

this.Shown += this.KeyboardSettingsForm_Shown;

_mForm.Show(); // show mdi-parent explicitly because only the application's start-up form shows automatically.

Answer 3

You're saying who is KeyboardSettingsForm's parent but where you're showing the parent?

_mForm = new mainForm(); //<---mdiparent not shown :(
this.MdiParent = _mForm;

Try this

_mForm = new mainForm();
_mForm.Show();//show your parent first
this.MdiParent = _mForm;

But even above code too makes only less sense. Did you mean to do something like this?

public partial class KeyboardSettingsForm : Form
{
    private mainForm _mForm;

    public KeyboardSettingsForm(mainForm mForm)
    {
        InitializeComponent();
        this._mForm = mForm;//Did you mean this?
        this.MdiParent = _mForm;

        this.Shown += new System.EventHandler(this.KeyboardSettingsForm_Shown);

    }
}