FindWindowA function does not yield the expected output in dart foreign function interface

Question

The following dart code's expected output is the handle to the file explorer window but the output always comes out to be 0 even though the file explorer window does exist!

import 'package:ffi/ffi.dart';
import 'dart:ffi';

void main() {
  DynamicLibrary dl = DynamicLibrary.open('user32.dll');
  final func = dl.lookupFunction<
      IntPtr Function(Pointer<Utf16>?, Pointer<Utf16>?),
      int Function(Pointer<Utf16>?, Pointer<Utf16>?)
    >('FindWindowA');

  print(func(nullptr, 'File Explorer'.toNativeUtf16()));
}

I have ran the function FindWindowA in a c++ program and it has returned the exptected output with the same input values that are NULL and 'File Explorer'.

In dart using null throws the error Invalid argument(s): argument value for ':ffi_param1' is null; hence the use of nullptr

If you don't want to do the ffi bit yourself, you can get this through the `win32` package: https://pub.dev/documentation/win32/latest/win32/FindWindow.html — Richard Heap, Jul 15 '22 at 22:30

score 0 · Accepted Answer · answered Jul 14 '22 at 06:41

FindWindowA does not take pointers to UTF-16 strings. The A in FindWindowA stands for "ANSI", which is Microsoft's way of indicating that it uses strings with single-byte code units encoded in the system's local encoding. (This is also indicated by its signature, which takes LPCSTR arguments.)

If you want to pass UTF-16 strings (which in Microsoft Windows are considered "wide strings"), then use FindWindowW.

FindWindowA function does not yield the expected output in dart foreign function interface

1 Answers1