The OpenEdge Hive

Sometimes you may need to force focus to a certain widget.
There must be several solutions but I found this one to be fairly reliable: make Windows think the user clicked on the widget using his left mouse button. 'Click' is a combination of 'buttondown' and 'buttonup' so it involves two messages, but I assume you might be allowed to skip one of them.
So if you want to apply focus to FILL-IN-1 you might say:

  run MouseClick(FILL-IN-1:HANDLE).

{windows.i}
  
PROCEDURE MouseClick :
 DEFINE INPUT PARAMETER hWidget AS HANDLE NO-UNDO.
 
 DEFINE VARIABLE ReturnValue AS INTEGER NO-UNDO.
 RUN PostMessage{&A} IN hpApi(hWidget:HWND,
                              {&WM_LBUTTONDOWN},
                              {&MK_LBUTTON},
                              0,
                              OUTPUT ReturnValue).
 RUN PostMessage{&A} IN hpApi(hWidget:HWND,
                              {&WM_LBUTTONUP},
                              0,
                              0,
                              OUTPUT ReturnValue).
END PROCEDURE.

Notes

You might have noticed the use of PostMessage instead of SendMessage like in apply the right mouse button. I have no idea why SendMessage doesn't work for the left mouse button.