C#

//FormLogIn.cs
using System;
using System.Windows.Forms;
public partial class FormLogIn : Form
{
    public event EventHandler LogInVerified;
    public FormLogIn()
    {
        InitializeComponent();
        btnOK.Click += new EventHandler(btnOK_Click);
    }

    void btnOK_Click(object sender, EventArgs e)
    {
        // Validate first
        OnLogInOK(EventArgs.Empty);
        Close();
    }
    protected virtual void OnLogInOK(EventArgs e)
    {
        EventHandler eh = LogInVerified;
        if (eh != null)
            eh(this, e);
    }
}

// FormMDI.cs
using System;
using System.Windows.Forms;
public partial class FormMDI : Form
{
    public FormMDI()
    {
        InitializeComponent();
        mnuLogIn.Click += new EventHandler(mnuLogIn_Click);
    }
    private void mnuLogIn_Click(object sender, EventArgs e)
    {
        FormLogIn formLogIn = new FormLogIn();
        formLogIn.LogInVerified += new EventHandler(formLogIn_LogInVerified);
        formLogIn.ShowDialog();
        formLogIn.LogInVerified -= formLogIn_LogInVerified;
        formLogIn.Dispose();
    }
    void formLogIn_LogInVerified(object sender, EventArgs e)
    {
        // Enable menus etc here
    }
}

DataGridView grid = new DataGridView();

foreach(string colName in ColumnNames)
{
    grid.Columns.Add(
            ([condition]) ?
                new DataGridViewColumn() :
                new MyColumn());
}