Reading from a text field in another application's window

Question

Is there a way for a Windows application to access another applications data, more specifically a text input field in GUI, and grab the text there for processing in our own

Answer 1

OK, I have somewhat figured this out.

The starting point is now knowing the window handle exactly, we only know partial window title, so first thing to do is find that main window:

...
EnumWindows((WNDENUMPROC)on_enumwindow_cb, 0);
...

which enumerates through all the windows on desktop. It makes a callback with each of these window handles:

BOOL CALLBACK on_enumwindow_cb(HWND hwndWindow, LPARAM lParam) {
    TCHAR wsTitle[2048];
    LRESULT result;
result = SendMessage(hwndWindow, WM_GETTEXT, (WPARAM) 2048, (LPARAM) wsTitle);
    ...

and by using the wsTitle and little regex magic, we can find the window we want.

By using the before mentioned Spy++ I could figure out the text edit field class name and use it to find wanted field in the hwndWindow:

hwndEdit = FindWindowEx(hwndWindow, NULL, L"RichEdit20W", NULL);

and then we can read the text from that field:

result = SendMessage(hwndEdit, WM_GETTEXT, (WPARAM) 4096, (LPARAM) wsText);

I hope this helps anyone fighting with the same problem!

Answer 2

HWND FindWindow(
LPCTSTR lpClassName,
LPCTSTR lpWindowName
);

http://msdn.microsoft.com/en-us/library/ms633499.aspx

Answer 3

You can also get text from a richedit control with EM_GETTEXTRANGE message, but it works only in the same process in which the control was created.

Answer 4

Look at AutoHotkey. If you need an API for your application, look at their sources. To prevent it, use a custom widget instead of WinForms, MFC or Win32 API. That is not foolproof, but helps.

Answer 5

About how to shield the application to prevent it, you could do many things. One way would be to have a own control to handle text input that build up the text from lets say a couple of labels placed where the text would be, or that draws the text graphically.

Answer 6

For reading text content from another application's text box you will need to get that text box control's window handle somehow. Depending on how your application UI is designed (if it has a UI that is) there are a couple of different ways that you can use to get this handle. You might use "FindWindow"/"FindWindowEx" to locate your control or use "WindowFromPoint" if that makes sense. Either way, once you have the handle to the text control you can send a "WM_GETTEXT" message to it to retrieve its contents (assuming it is a standard text box control). Here's a concocted sample (sans error checks):

HWND hwnd = (HWND)0x00310E3A;
char szBuf[2048];
LONG lResult;

lResult = SendMessage( hwnd, WM_GETTEXT, sizeof( szBuf ) / sizeof( szBuf[0] ), (LPARAM)szBuf );
printf( "Copied %d characters.  Contents: %s\n", lResult, szBuf );

I used "Spy++" to get the handle to a text box window that happened to be lying around.

As for protecting your own text boxes from being inspected like this, you could always sub-class your text box (see "SetWindowLong" with "GWL_WNDPROC" for the "nIndex" parameter) and do some special processing of the "WM_GETTEXT" message to ensure that only requests from the same process are serviced.