GetWindowTextA, GetWindowText returns empty value

问题:

I'm trying to list and get the content of Edit Controls from an external Window in C++ / Java, unfortunately with no success.

When I call GetWindowText or GetWindowTextA it returns an empty value on Edit Controls, I know there are some differences between GetWindowText / GetWindowTextW and GetWindowTextA but I don't know What I'm doing wrong since it works on all other controls.

Here the C++ Code:

BOOL CALLBACK EnumChildProc(HWND hwnd, LPARAM lParam)
{
    cout <<"----------CHILD------------"<<endl;
    char class_name[80];
    char title[80];
    GetClassName(hwnd,class_name, sizeof(class_name));
    GetWindowText(hwnd,title,sizeof(title));
    cout <<"\tWindow title: "<<title<<endl;
    cout <<"\tClass name: "<<class_name<<endl<<endl;
     return TRUE;
}

Java Code:

User32.INSTANCE.EnumChildWindows(hWnd, new User32.WNDENUMPROC() {
    @Override
    public boolean callback(Pointer   hWnd, Pointer   arg) {
        byte[] windowClassx = new byte[512];
        User32.INSTANCE.GetClassNameA(hWnd, windowClassx, 512);
        String wClass = Native.toString(windowClassx);
        System.out.println(" - Found sub window / control class: " + new String(windowClassx).trim());
        if (wClass.toLowerCase().equals("edit")){
            byte[] windowTextx = new byte[128];
            user32.GetWindowText(hWnd, windowTextx, 128);
            String wText = Native.toString(windowTextx);
            System.out.println(wText);
        }

        return true;
    }
}, null);  

回答1:

I'm not sure what is causing your problem, but this has worked just fine for me:

byte[] windowText = new byte[512];
User32.INSTANCE.GetWindowTextA(hWnd, windowText, 512);
String wText = Native.toString(windowText).trim();

---

Edit
You should get the edit text a different way, via

User32.SendMessageA(editHwnd, User32.WM_GETTEXT, paramWPARAM, lParamStr);

e.g.,

import com.sun.jna.Native;
import com.sun.jna.platform.win32.WinDef.HWND;
import com.sun.jna.platform.win32.WinDef.LPARAM;
import com.sun.jna.platform.win32.WinDef.LRESULT;
import com.sun.jna.platform.win32.WinDef.WPARAM;
import com.sun.jna.win32.StdCallLibrary;

public class GetTextInNotePad {
   public static final String NOTEPAD_CLASS = "Notepad";
   public static final String EDIT_CLASS = "Edit";

   interface User32 extends StdCallLibrary {
      User32 INSTANCE = (User32) Native.loadLibrary("user32", User32.class);
      int WM_SETTEXT = 0x000c;
      int WM_GETTEXT = 0x000D;

      HWND FindWindowA(String lpClassName, String lpWindowName);
      HWND FindWindowExA(HWND hwndParent, HWND hwndChildAfter, String lpClassName,
            String lpWindowName);
      LRESULT SendMessageA(HWND paramHWND, int paramInt, WPARAM paramWPARAM, LPARAM paramLPARAM);
      LRESULT SendMessageA(HWND editHwnd, int wmGettext, long l, byte[] lParamStr);
      int GetClassNameA(HWND hWnd, byte[] lpString, int maxCount);
   }

   public static void main(String[] args) {
      User32 user32 = User32.INSTANCE;
      String lpClassName = "Notepad";
      HWND notePadHwnd = user32.FindWindowA(lpClassName , null);
      HWND editHwnd = user32.FindWindowExA(notePadHwnd, null, EDIT_CLASS, null); 
      byte[] lParamStr = new byte[512];
      LRESULT resultBool = user32.SendMessageA(editHwnd, User32.WM_GETTEXT, 512, lParamStr);

      System.out.println("lParamStr: " + Native.toString(lParamStr));
   }
}