Createwindowex invalid handle error

Question

I am using jna functions to call winapi

public muFunction(){
  Magnification.INSTANCE.MagInitialize();
  RECT desktopRect= new RECT();
  HWND desktop = User32.INSTANCE.GetDesktopWindow();
  User32Extra.INSTANCE.GetWindowRect(desktop, desktopRect);
  HINSTANCE hInstance =Kernel32.INSTANCE.GetModuleHandle(null);

  HWND lsm = User32Extra.INSTANCE.FindWindow(null, "MyWindow");
  HWND hwndMag = User32Extra.INSTANCE.CreateWindowEx(new DWORD(0x00000000L), "Magnifier", "MagnifierWindow", new DWORD(0x40000000L|0x0001L|0x10000000L), desktopRect.left, desktopRect.top, desktopRect.right-desktopRect.left, desktopRect.bottom-desktopRect.top, desktop, null, hInstance, null);
  System.out.println(Native.getLastError()); // return 6 as error
}

Magnification Api code

public interface Magnification extends StdCallLibrary {

    Magnification INSTANCE = (Magnification) Native.loadLibrary("magnification", Magnification.class,
                                                W32APIOptions.DEFAULT_OPTIONS);

    public Boolean MagInitialize();

    public boolean MagSetWindowFilterList(HWND hwndMag, DWORD dword, int i,
            HWND[] excludeHWNDs);

    public boolean MagSetWindowSource(HWND hwndMag, RECT sourceRect);

}

I am getting ERROR_INVALID_HANDLE error. What is wrong with my code.

Thanks

Answer 1

There are a lot of problems with your code. You don't perform error checking, as has been exhaustively covered in the comments. You really need to sort that out.

You also use magic constants for window style. Please declare named constants so that future readers (i.e. you) can make sense of the code. The key one is your use of WS_CHILD. You can't make the desktop window be the parent of your child window. You'll need to provide another window to be the parent.