[Windows] Setting min Window size does not work

[DenuxPlays]

Hey,

I tried to limit the window size for my flutter app but it does not appear to work.
Code:

void _configureWindow() {
  if (!PlatformUtils.isDesktop) {
    debugPrint('Window configuration is only supported on desktop platforms.');
    return;
  }

  final window = nativeapi.WindowManager.instance.getCurrent();
  if (window == null) {
    debugPrint('Failed to get current window for configuration.');
    return;
  }

  window.setMinimumSize(windowMinWidth, windowMinHeight);
  window.show();
  window.focus();
  debugPrint("Window size set to: ${currentWindowSize.width}x${currentWindowSize.height}");
}

The output from the code is:
Window size set to: 0.0x0.0

Is there something I did wrong?

[lijy91]

Analysis of your issue

Thanks for reporting this. I looked into the code and found two separate problems: one in your code, and one in the library.

---

Problem 1: setMinimumSize ≠ setSize (conceptual confusion in your code)

setMinimumSize sets a constraint — it prevents the user from resizing the window smaller than the given dimensions. It does not change the actual window size.

Right now your code only sets the minimum size but never actually sizes the window:

window.setMinimumSize(windowMinWidth, windowMinHeight); // sets a constraint only
window.show();
window.focus();
debugPrint("Window size set to: ${currentWindowSize.width}x${currentWindowSize.height}");

If you want to set the window to a specific size, you need to call setSize:

window.setSize(windowMinWidth, windowMinHeight); // actually resize the window
window.setMinimumSize(windowMinWidth, windowMinHeight); // optionally prevent making it smaller

Problem 2: currentWindowSize is undefined

The variable currentWindowSize is never declared or assigned in your snippet. 0.0x0.0 is the default value for an uninitialized Size in Dart. You probably meant to use window.size:

final currentWindowSize = window.size;
debugPrint("Window size set to: ${currentWindowSize.width}x${currentWindowSize.height}");

Corrected version of your code

void _configureWindow() {
  if (!PlatformUtils.isDesktop) {
    debugPrint('Window configuration is only supported on desktop platforms.');
    return;
  }

  final window = nativeapi.WindowManager.instance.getCurrent();
  if (window == null) {
    debugPrint('Failed to get current window for configuration.');
    return;
  }

  window.setSize(windowMinWidth, windowMinHeight);
  window.setMinimumSize(windowMinWidth, windowMinHeight);
  window.show();
  window.focus();

  final currentWindowSize = window.size;
  debugPrint("Window size set to: ${currentWindowSize.width}x${currentWindowSize.height}");
}

---

Problem 3: Library bug — SetMinimumSize is a no-op on Windows

Even after fixing your code, setMinimumSize still won't work because the Windows implementation is a placeholder that does nothing.

In packages/cnativeapi/cxx_impl/src/platform/windows/window_windows.cpp:

void Window::SetMinimumSize(Size size) {
  // Windows minimum size would be handled in WM_GETMINMAXINFO message
  // This is a placeholder implementation
}

Size Window::GetMinimumSize() const {
  return {0, 0}; // always returns zero
}

To actually enforce minimum/maximum sizes on Windows, the library needs to:

1. Store the min/max size in the Window::Impl class
2. Handle WM_GETMINMAXINFO in WindowProc to set MINMAXINFO.ptMinTrackSize / ptMaxTrackSize
3. Return stored values from GetMinimumSize() / GetMaximumSize()

This is a real library bug that needs to be fixed in the C++ Windows backend. I can help implement the fix if you'd like.

[DenuxPlays]

Thanks for your answer.
The goal is to set a constraint not to set the window size.
The "correct" code (which I forgot to copy):

void _configureWindow() {
  if (!PlatformUtils.isDesktop) {
    debugPrint('Window configuration is only supported on desktop platforms.');
    return;
  }

  final window = nativeapi.WindowManager.instance.getCurrent();
  if (window == null) {
    debugPrint('Failed to get current window for configuration.');
    return;
  }

  window.setMinimumSize(windowMinWidth, windowMinHeight);
  window.show();
  window.focus();

  final currentWindowSize = window.minimumSize;
  debugPrint("Window size set to: ${currentWindowSize.width}x${currentWindowSize.height}");
}

currentWindowSize is named badely it was just for debugging.

Problem 2 explains why it does not work on windows.
I do not have time to implement it.
I used your old package window_manager for now.

Thank you for the answer.