java - Using JNA to get GetForegroundWindow();

Question

I asked a similar question on a previous thread (https://stackoverflow.com/questions/5206633/java-find-out-what-application-window-is-in-focus) but I was guided to use JNI, and I'm not having much success with it... I've read some tutorials and while some work fine, others don't I still can't get the information I need, which is the title of the window on the foreground.

Now I'm looking into JNA but I can't figure out how to access GetForegroundWindow() ... I think I can print the text once I get the handle to the window using this code (found on another thread):

import com.sun.jna.*;
import com.sun.jna.win32.*;

public class jnatest {
    public interface User32 extends StdCallLibrary {
        User32 INSTANCE = (User32) Native.loadLibrary("user32", User32.class);

        int GetWindowTextA(PointerType hWnd, byte[] lpString, int nMaxCount);
    }

    public static void main(){
        byte[] windowText = new byte[512];

        PointerType hwnd = //GetForegroundWindow() (?)...
        User32.INSTANCE.GetWindowTextA(hwnd, windowText, 512);
        System.out.println(Native.toString(windowText));

    }
}

Any suggestions? Thanks!

Answer 1

How about simply adding a method call to match the native GetForegroundWindow to your interface, something like so:

import com.sun.jna.*;
import com.sun.jna.platform.win32.WinDef.HWND;
import com.sun.jna.win32.*;

public class JnaTest {
   public interface User32 extends StdCallLibrary {
      User32 INSTANCE = (User32) Native.loadLibrary("user32", User32.class);
      HWND GetForegroundWindow();  // add this
      int GetWindowTextA(PointerType hWnd, byte[] lpString, int nMaxCount);
   }

   public static void main(String[] args) throws InterruptedException {
      byte[] windowText = new byte[512];

      PointerType hwnd = User32.INSTANCE.GetForegroundWindow(); // then you can call it!
      User32.INSTANCE.GetWindowTextA(hwnd, windowText, 512);
      System.out.println(Native.toString(windowText));
   }
}