Question

I’m trying to come up with a solution for setting up a notification when focus enters a text field. The end goal in mind is to recreate the type of functionality you see on mobile devices with on screen keyboards.

So far I’ve been exploring SetWinEventHook with EVENT_OBJECT_FOCUS and GetGUIThreadInfo with GUI_CARETBLINKING.

From the docs:

EVENT_OBJECT_FOCUS

An object has received the keyboard focus. The system sends this event
for the following user interface elements: list-view control, menu
bar, pop-up menu, switch window, tab control, tree view control, and
window object.

GUI_CARETBLINKING The caret’s blink state. This bit is set if the
caret is visible.

Using these methods I’ve come up with this solution:

void TextInputHelper::setupEventHook(FREContext iCtx)
{
    ctx = iCtx;
    CoInitialize(NULL);

    evHook = SetWinEventHook(EVENT_OBJECT_FOCUS, EVENT_OBJECT_END, NULL,
    handleEventObjectFocus, 0, 0,
    WINEVENT_OUTOFCONTEXT | WINEVENT_SKIPOWNPROCESS);

}


void CALLBACK handleEventObjectFocus(HWINEVENTHOOK hook, DWORD evt, HWND hwnd,
                                 LONG idObj, LONG idChild,    DWORD thread, DWORD time)
 {
    GUITHREADINFO threadInfo;
    threadInfo.cbSize = sizeof(GUITHREADINFO);

    BOOL result = GetGUIThreadInfo(thread, &threadInfo);


    if(threadInfo.flags & GUI_CARETBLINKING)
    {

        //text field focus
    }


}

This does seem to work in some cases but its definitely not reliable. Programs like Notepad an IE seem to work fine but others like Firefox do not. This also will not work for things like text fields on websites because it doesn’t look like handleEventObjectFocus will get called.

Does anyone know of another way to approach this problem? I’ve been searching around and it seems like I might be looking for something in the Accessibility APIs but I haven’t been able to dig up to much on it.

Thanks!

edit

To clarify, I’m looking to receive a notification when focus enters any text field. This application is a win32 dll and will never have focus its self.

Answer 1

If you’re using standard Windows controls WM_SETFOCUS should do the trick. No need to get fancy with hooking etc.

EDIT: For system wide behavior you can check out SetWindowsHookEx. To catch events system-wide you need to use it from within a DLL. You can use a combination of hooks including one that catches WM_SETFOCUS.