A dart code snippet to support longpress display popup dialog feature, when finger leaves, the popup will be closed too.

demo_of_longpress_pop_feature.dart

// Implement a function to create OverlayEntry
OverlayEntry getMyOverlayEntry({
  @required BuildContext context,
  SomeData someData,
}) {
  return OverlayEntry(
      builder: (context) {
        return AlertDialog(child: SomeWidgetAgain());
      }
  );
}

// In the widget where you want to support long press feature
OverlayEntry myOverayEntry;

GestureDetector(
    onLongPress: () {
      myOverayEntry = getMyOverlayEntry(context: context, someData: someData);
      Overlay.of(context).insert(myOverayEntry);
    },
    onLongPressEnd: (details) => myOverayEntry?.remove(),

    child: SomeWidgerHere(),
)