VisibilityDetector not working with AppLifecycleState

[yjouyang]

When my app go to background or come back to foreground, nothing is called in VisibilityDetector. Is there any way to do this?

[yjouyang]

I've done something like this:

extension VisibilityDetector on Widget {
  Widget toVisibilityDetector(String key, Function(bool visible) callback) {
    final appLifecycleObserver = _AppLifecycleObserver(callback);
    var visible = false;
    return google.VisibilityDetector(
      key: Key(key),
      child: this,
      onVisibilityChanged: (google.VisibilityInfo info) {
        final isNowVisible = info.visibleFraction > 0;
        if (isNowVisible == visible) {
          return;
        }
        visible = isNowVisible;
        callback(visible);
        if (visible) {
          WidgetsBinding.instance.addObserver(appLifecycleObserver);
        } else {
          WidgetsBinding.instance.removeObserver(appLifecycleObserver);
        }
      },
    );
  }
}

class _AppLifecycleObserver extends WidgetsBindingObserver {

  final Function(bool visible) callback;

  _AppLifecycleObserver(this.callback);

  @override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    super.didChangeAppLifecycleState(state);
    callback(state == AppLifecycleState.resumed);
  }
}

Any suggestions?

[jamesderlin]

Sorry, I somehow missed this when it was filed.

VisibilityDetector reports only in-app changes to widget visibility, not changes due to the entire application going to the background or returning to the foreground. You will need to deal with AppLifecycleState changes yourself. (That said, your approach of creating a _AppLifecycleObserver object and an extra callback per VisibilityDetector seems wasteful. A better approach might be to keep track of which VisibilityDetectors are expected to be visible and have a single AppLifecycleState observer trigger callbacks for all of them.)

I'm currently leaning toward leaving this as the application's responsibility, but I'll have to think about this for a bit. Feel free to convince me in either direction.

[yjouyang]

People usually want to detect the visibility of view because they want to reload data when the view becomes visible. So whether the view becomes visible because the application come to foreground or because it is added to the widget tree, they are not so different, in which case data should be reloaded

[CivelXu]

Is there a good solution to this problem?

[oscarshaitan]

you should use
didChangeAppLifecycleState
on the StatefulWidget

that works fine in my case to controll a stream, is pretty well explained here
https://api.flutter.dev/flutter/widgets/WidgetsBindingObserver-class.html

[jillellamudisurya]

@jamesderlin This thing might need to add in the documentation, because everyone will think that the visibility will get reported if app went to background state.