Have fun with the MDI client area

Introduction

When you designate a form as an MDI container, the .NET framework docks an MdiClient control on your form. Unfortunately, the framework does not expose any of the properties of this control, which makes it difficult to change things like the client area background color or to center controls. Difficult at first glance, that is.

How it is done

The MdiClient control is a control just like any other, even though it is managed implicitly by the framework. As a control, it can be found in the Form's Controls collection. This is how you can get it using VB:

Public Class Form1

    Private ClientControl As MdiClient

    Public Sub New()
        InitializeComponent()

        ClientControl = Nothing
        For Each Ctl As Control In Me.Controls
            ClientControl = TryCast(Ctl, MdiClient)
            If ClientControl IsNot Nothing Then Exit For
        Next
    End Sub

End Class

Here is the C# version:

public partial class Form1 : Form
{
    private MdiClient ClientControl;

    public Form1()
    {
        InitializeComponent();
        ClientControl = null;
        foreach (Control Ctl in this.Controls)
        {
            ClientControl = Ctl as MdiClient;
            if (ClientControl != null) break;
        }
    }
}

Once you have verified that ClientControl is not Nothing (or null), you can treat it just like any other control. Perhaps, your application can point to a production database and one used just for testing? Change the BackColor property to show this. Do you want a logo to remain centered when the MDI form is resized? Drop a PictureBox into the client area and then use this code in the Form's Resize event:

PictureBox1.Left = (ClientControl.Width \ 2) - (PictureBox1.Width \ 2)
PictureBox1.Top = (ClientControl.Height \ 2) - (PictureBox1.Height \ 2)

C#:

PictureBox1.Left = (int)((ClientControl.Width / 2) - (PictureBox1.Width / 2));
PictureBox1.Top= (int)((ClientControl.Height/ 2) - (PictureBox1.Height/ 2));

Avenues of exploration

When you set IsMdiContainer to true, the framework does more than just add a MdiControl onto the form. You can see this clearly if you try something like this:

If ClientControl IsNot Nothing Then
    ClientControl.Dock = DockStyle.Right
    ClientControl.Width = Me.ClientRectangle.Width \ 2
End If

C#:

if (ClientControl != null)
{
    ClientControl.Dock = DockStyle.Right;
    ClientControl.Width = (int) (this.ClientRectangle.Width / 2)
}

The part of the form that is exposed is set to SystemColors.AppWorkspace, regardless of what color you give to the BackColor of ClientControl and the form. I have not yet figured out how to change this to match the form's background, but when I do, the ability to dynamically resize the MdiClient would open up some interesting possibilities.