C#

using System.Windows.Forms;<br />
using System.Collections.Generic;<br />
using System;<br />
<br />
public class Test<br />
{<br />
    static void Main()<br />
    {<br />
        Application.Run(new MainForm());<br />
    }<br />
}<br />
<br />
class MainForm : Form<br />
{<br />
    public MainForm()<br />
    {<br />
        WindowState = FormWindowState.Maximized;<br />
        IsMdiContainer = true;<br />
        Form frm = new Childform();<br />
        frm.MdiParent = this;<br />
        frm.Show();<br />
        Form frm2 = new Childform();<br />
        frm2.MdiParent = this;<br />
        frm2.Show();<br />
        frm2.Left = 2000;<br />
    }<br />
}<br />
<br />
class Childform : Form<br />
{<br />
    DataGridView grid;<br />
    Control LastFocus = null;<br />
<br />
    public Childform()<br />
    {<br />
        ToolStripContainer tc = new ToolStripContainer();<br />
<br />
        grid = new DataGridView();<br />
        grid.Columns.Add(new DataGridViewTextBoxColumn());<br />
        grid.EditMode = DataGridViewEditMode.EditOnEnter;<br />
        grid.Top = 120;<br />
        grid.Height = 300;<br />
        Controls.Add(tc);<br />
        tc.ContentPanel.Controls.Add(new MyUserControl());<br />
<br />
        tc.ContentPanel.Controls.Add(grid);<br />
        this.Activated += new EventHandler(Childform_Activated);<br />
        this.Deactivate += new EventHandler(Childform_Deactivate);<br />
    }<br />
<br />
    void Childform_Activated(object sender, EventArgs e)<br />
    {<br />
        if (this.LastFocus != null)<br />
            this.LastFocus.Focus();<br />
    }<br />
<br />
    void Childform_Deactivate(object sender, EventArgs e)<br />
    {<br />
        this.LastFocus = this.ActiveControl;<br />
        while (LastFocus is IContainerControl)<br />
            LastFocus = ((IContainerControl)LastFocus).ActiveControl;<br />
    }<br />
}<br />
<br />
class MyUserControl : UserControl<br />
{<br />
    internal MyUserControl()<br />
    {<br />
        Height = 100;<br />
        Controls.Add(new TextBox());<br />
    }<br />
}