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Win32 API GUI in Object-Oriented style with some helpers. Uses package `win32` and `dart:ffi`.

win32_gui #

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Win32 API GUI in Object-Oriented style with some helpers. Uses package win32 and dart:ffi.

Screenshot #

Example screenshot:

Example screenshot

Usage #

Here's a simple Hello World window:

import 'dart:io';

import 'package:win32_gui/win32_gui.dart';

Future<void> main() async {
  // Your custom main Window class (declared bellow):
  var mainWindow = MainWindow(
    width: 640,
    height: 480,

  // Create the window:
  await mainWindow.create();
  // Exit when the Window is closed and destroyed:
  // See `MainWindow.processClose` below:
  mainWindow.onDestroy.listen((window) {
    print('-- Window Destroyed> $window');

  // Show the main Window:;

  // Run the Win32 Window message loop.
  await Window.runMessageLoopAsync();

// A custom main Window:
class MainWindow extends Window {
  // Declare the main window custom class:
  static final mainWindowClass = WindowClass.custom(
    className: 'mainWindow',
    windowProc: Pointer.fromFunction<WindowProc>(mainWindowProc, 0),
    bgColor: RGB(255, 255, 255),
    useDarkMode: true,
    titleColor: RGB(32, 32, 32),

  // Redirect to default implementation [WindowClass.windowProcDefault].
  static int mainWindowProc(int hwnd, int uMsg, int wParam, int lParam) =>
                  hwnd, uMsg, wParam, lParam, mainWindowClass);
  MainWindow({super.width, super.height})
          : super(
    defaultRepaint: false, // Tells that `repaint()` below will be used. 
    windowName: 'Win32 GUI - Example', // The Window title.
    windowClass: mainWindowClass,
    windowStyles: WS_MINIMIZEBOX | WS_SYSMENU,
  ) ;

  late final String imageDartLogoPath;
  late final String iconDartLogoPath;
  // Load resources (called by `create()`):
  Future<void> load() async {
    imageDartLogoPath = await Window.resolveFilePath(
    iconDartLogoPath = await Window.resolveFilePath(

  // Called when processing a `WM_CREATE` message (generated by `create()`):
  void build(int hwnd, int hdc) {, hdc);

    SetTextColor(hdc, RGB(255, 255, 255));
    SetBkColor(hdc, RGB(96, 96, 96));

    // Sets the Window icon: 
  // Customize close operation:
  bool? processClose() {
    // Inform default close behavior (`destroy()` Window):
    return null;
  // Custom repaint. Called when processing a `WM_PAINT` message and `this.defaultRepaint = false`:
  void repaint(int hwnd, int hdc) {
    // Loads a 24-bits Bitmap:
    var hBitmap = loadImageCached(imageDartLogoPath);
    // Get the Bitmap dimensions:
    var imgDimension = getBitmapDimension(hBitmap);

    // Valid Bitmap:
    if (imgDimension != null) {
      var imgW = imgDimension.width;
      var imgH = imgDimension.height;
      // Center image horizontally:
      final x = (dimensionWidth - imgW) ~/ 2;
      final y = 10;

      // Draws the Bitmap copying its bytes to this Window.
      drawImage(hdc, hBitmap, x, y, imgW, imgH);

Win32 Message Loop #

A win32 application requires a message loop. Depending on the implementation of the win32 message loop, it will block the Dart VM loop, responsible for dispatching Future executions and Isolate messages:

  final msg = calloc<MSG>();
  while (GetMessage(msg, NULL, 0, 0) != 0) {

The code above is equivalent to calling Window.runMessageLoop(), and it will block any other Dart code from being executed, such as timers, listeners, or any dispatched Future.

To circumvent this significant issue, you can make use of the Window.runMessageLoopAsync() function. This function not only dispatches win32 messages but also enables the dispatch of Dart code by intermittently yielding control.

  // Run the Win32 Window message loop until the application completes.
  await Window.runMessageLoopAsync();

If you need to run the win32 loop for a specific duration:

  // Run the Win32 Window message loop for 10s:
  await Window.runMessageLoopAsync(timeout: Duration(seconds: 10));

...or while a certain condition holds true.

  // Run the Win32 Window message loop while the `mainWindow` is minimized:
  await Window.runMessageLoopAsync(condition: () => mainWindow.isMinimized);

Features and bugs #

Please file feature requests and bugs at the issue tracker.

Contribution #

Your assistance and involvement within the open-source community is not only valued but vital. Here's how you can contribute:

  • Found an issue?
    • Please fill a bug report with details.
  • Wish a feature?
    • Open a feature request with use cases.
  • Are you using and liking the project?
    • Advocate for the project: craft an article, share a post, or offer a donation.
  • Are you a developer?
    • Fix a bug and send a pull request.
    • Implement a new feature.
    • Improve the Unit Tests.
  • Already offered your support?
    • Sincere gratitude from myself, fellow contributors, and all beneficiaries of this project!

By donating one hour of your time, you can make a significant contribution, as others will also join in doing the same. Just be a part of it and begin with your one hour.

Author #

Graciliano M. Passos: gmpassos@GitHub.

License #

Apache License - Version 2.0

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Win32 API GUI in Object-Oriented style with some helpers. Uses package `win32` and `dart:ffi`.

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#win32 #windows #ffi


API reference


Icon for licenses.Apache-2.0 (LICENSE)


collection, ffi, logging, resource_portable, win32


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