Is there a way to show a warning dialog when closing a browser tab running a flutter app?

user_10651505 0
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I would like to indicate to the user that there's a file being downloaded when they try to close the tab in my flutter web app. Is there a way of hooking into the app to detect this behavior and to show such a warning message?

Warning popup

flutter-web flutter popup
1 Answers

You may register code for a BeforeUnloadEvent like this:

import 'dart:html' as html;

/// Subscription on application termination warning
StreamSubscription? _onBeforeUnloadSubscription;

//enable warning for closing browser tab:
_onBeforeUnloadSubscription = registerOnBeforeUnload("Transfers in progress!");

//disable warning for closing browser tab:
stopBeforeUnloadHandler();


StreamSubscription? registerOnBeforeUnload(String warningMessage) {
  StreamSubscription<html.BeforeUnloadEvent> _onBeforeUnloadSubscription;

  _onBeforeUnloadSubscription = html.window.onBeforeUnload.listen((e) async {
    (e as html.BeforeUnloadEvent).returnValue = warningMessage;
    return Future.value(warningMessage);
  }) as StreamSubscription<html.BeforeUnloadEvent>;
  return _onBeforeUnloadSubscription;
}

void stopBeforeUnloadHandler() {
  if (_onBeforeUnloadSubscription != null) {
    _onBeforeUnloadSubscription!.cancel();
    _onBeforeUnloadSubscription = null;
  }
}
user_38770170
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