WinAPI - Problem to append text to an editbox

Question

Hi, I created a simple window with a multiline Edit Control:

Edit = CreateWindowEx(WS_EX_CLIENTEDGE, TEXT("EDIT"), NULL,
                    WS_CHILD | WS_VISIBLE | ES_MULTILINE,
                    20, 200, 200, 200,
                    hWnd, (HMENU)EDIT, GetModuleHandle(NULL), NULL);

If I set text using a WM_SETTEXT message, I don't get errorrs, but if I use EM_REPLACESEL I get Error 5 (ERROR_ACCESS_DENIED):

SendMessage(GetDlgItem(hWnd, EDIT), EM_REPLACESEL, 0, (LPARAM)TEXT("\r\nSome text"));
if (GetLastError()) {
    /* Error 5 ERROR_ACCESS_DENIED */
}

Same problem with EM_SETSEL:

SendMessage(GetDlgItem(hWnd, EDIT), EM_SETSEL, (WPARAM)(0),(LPARAM)(-1));
SendMessage(GetDlgItem(hWnd, EDIT), EM_REPLACESEL, 0, (LPARAM)TEXT("\r\nSome text"));
if (GetLastError()) {
    /* Error 5 ERROR_ACCESS_DENIED */
}

I noticed that if I send a WM_SETFOCUS message before the EM_REPLACESEL there are no error:

SendMessage(GetDlgItem(hWnd, EDIT), WM_SETFOCUS, (WPARAM)GetDlgItem(hWnd, EDIT), 0);
SendMessage(GetDlgItem(hWnd, EDIT), EM_REPLACESEL, 0, (LPARAM)TEXT("\r\nSome text"));
if (GetLastError()) {
    /* NO ERRORS */
}

How can I resolve this problem? Do I have to send a WM_SETFOCUS message before the EM_REPLACESEL one every time I want to append some text to my Editbox?

Thanks for help!

Answer 1

You can simply use a EM_SETSEL first and then do your EM_REPLACESEL.

Example:

SendMessage(hwnd, EM_SETSEL, WPARAM(0), LPARAM(-1) );
SendMessage(hwnd, EM_REPLACESEL, WPARAM(TRUE), LPARAM(str) );

Answer 2

You're most likely getting access denied because of UIPI.

Is the Edit box created by the same application that's attempting to send messages? If not, the application doing the SendMessage probably has a lower UIPI level than the application that owns the Edit.

If you do, in fact, own both the application that created the Edit control and the application sending the messages, you can allow specific messages in by using ChangeWindowMessageFilterEx.

ChangeWindowMessageFilterEx(hwndOfWindowReceivingMessage, EM_REPLACESEL, 
    MSGFLT_ALLOW, NULL);