C#

private void Form1_Load(object sender, EventArgs e)
{
    MdiClient ctlMDI;
    //' Loop through all of the form's controls looking
    //' for the control of type MdiClient.
    foreach (Control ctl in this.Controls)
    {
        try
        {
            // Attempt to cast the control to type MdiClient.
            ctlMDI = (MdiClient)ctl;

            // Set the BackColor of the MdiClient control.
            ctlMDI.BackColor = Color.White;
        }
        catch (InvalidCastException exc)
        {
            // Catch and ignore the error if casting failed.
        }
    }
}

Alisaunder wrote:

try
{
// Attempt to cast the control to type MdiClient.
ctlMDI = (MdiClient)ctl;

private void MdiClientExample()
{
    foreach (Control c in this.Controls)
    {
        if (c is MdiClient)
        {
            MdiClient mc = (MdiClient)c;
            ...
        }
    }
}

Alisaunder wrote:

Funny, I have a feeling you weren't taught with original code either.

Alisaunder wrote:

This is another example of someone thinking the op should be equally as skilled
as the person responding.

foreach(Control c in Controls) {
 MdiClient mdi = c as MdiClient;
 if(mdi != null) { ... }
}

Alisaunder wrote:

And yet neither of you are displaying an alternative that is better?

//
// assume you have loaded a valid image from an embedded resource
// into the variable of Type Bitmap named 'mdiBackGround'
//
private MdiClient theMDIClientControl;
//
foreach (Control theControl in this.Controls) [2]
{
    if (theControl is MdiClient)
    {
        theMDIClientControl = theControl as MdiClient;
        break;
    }
}

if (theMDIClientControl != null) theMDIClientControl.BackgroundImage = mdiBackGround;

Alisaunder wrote:

Also adding Try and catch is error controlling which I don't care who you are
is still considered good practice