C++ MFC Refresh Window - c++

Question

I am using Visual Studio 2010 with MFC and I am trying to make a rectangle that is red when a device is disconnected and green when it is. I have made the rectangle with the following code:
CRect lConnectStatus;
GetDlgItem( IDC_CONNECT_STATUS ) -> GetClientRect( &lConnectStatus );
GetDlgItem( IDC_CONNECT_STATUS ) -> ClientToScreen( &lConnectStatus );
ScreenToClient( &lConnectStatus );
mConnected.Create( GetSafeHwnd(), 10000 );
mConnected.SetPosition( lConnectStatus.left, lConnectStatus.top, lConnectStatus.Width(), lConnectStatus.Height() );
if( mDevice.IsConnected() ){
mConnected.SetBackgroundColor(0, 255, 0);
}
else{mConnected.SetBackgroundColor(0, 0, 255);}
I inserted this snippet into the OnInitDlg method and the rectangle does appear, but it doesn't change to green when the device gets connected. Is there anyway I can refresh the window so that the code is executed again and the colour changes to green?

Answer 1

What type of control is IDC_CONNECT_STATUS? If it is a static control you can eliminate all this code and handle WM_CTLCOLOR_STATIC in the parent dialog. Your message handler for that message will control the color of the static control. To refresh the static control call Invalidate on that control. That will cause it to call your WM_CTLCOLOR_STATIC message handler.

Answer 2

Solved It, As I am new to C++ I didn't know that putting the code snippet into the OnInitDlg() method wouldn't work. So I put the code into the OnPaint()method and used the functions Invalidate() and UpdateWindow() to force the window to refresh when the device was connected/disconnected. Thanks for your help.
Edit Thanks to Barmak for suggesting not to create the control in the OnPaint() method. I have updated the code below.
program::OnInitDlg(){
CRect lConnectStatus;
GetDlgItem( IDC_CONNECT_STATUS ) -> GetClientRect( &lConnectStatus );
GetDlgItem( IDC_CONNECT_STATUS ) -> ClientToScreen( &lConnectStatus );
ScreenToClient( &lConnectStatus );
mConnected.Create( GetSafeHwnd(), 10000 );
mConnected.SetPosition( lConnectStatus.left, lConnectStatus.top, lConnectStatus.Width(), lConnectStatus.Height() );
}
program::OnPaint(){
if( mDevice.IsConnected() ){
mConnected.SetBackgroundColor(0, 255, 0);
}
else{mConnected.SetBackgroundColor(0, 0, 255);}
}
program::Connect(){
Invalidate();
UpdateWindow();
}
program::disconnect(){
Invalidate();
UpdateWindow();
}