Visual C++ :: MFC Proper Usage Of Sending Message To Dialog To Activate

I have finally got around to developing C++ & MFC using Visual Studio 2012, to build a full GUI Windows application (not sure if I have made the right choice). Though admittedly in two months time I do have a dialog window at my beck and call.

Now I have discovered a flaw (suspect) partially caused by the design of this program not all following the same principles, nor written by the same people and long predates me. Let describe the situation.

I have a dialog I have created as a class which has a combo box. The list of items are populate during the OnInitDialog() function just fine, except if the file where the detail is not yet read from that combo box would not have any items other than the default. This is to be expected in the use of the program, so fine.

However, if the dialog (modeless) was already open and active, when the user went up to and selected the menu command (main window) to read that file that CPtrList data structure that held that data would not populate that Combo box on my dialog.

So what I would like when I am done reading the files contents is to detect if my dialog is opened and if so send it a message to Activate (force a call to OnActivate()). I have gone to the event list for the dialog and exposed this event handler from the resource editor just fine.

I see the syntax of OnActivate() is

void MyClass::OnActivate(UINT nState, CWnd* pWndOther, BOOL bMinimalized);

So nState is an Unsigned Int of the current state of the thread/window (not sure)?

CWnd* pWndOther is the CWnd of my other Window that wants my dialog to activate I think which is the main application since it was on the a menu that this function was called to read the file.

bMinimalized is whether my dialog is mimalized(?)