Outdated example about open-mail-app-flutter HOT 5 CLOSED

  Future<void> _openMailApp(BuildContext context) async {
    // Android: Will open mail app or show native picker.
    // iOS: Will open mail app if single mail app found.
    final result = await OpenMailApp.openMailApp();
    Route<Object?> _dialogBuilder(BuildContext context, Object? arguments) {
      return DialogRoute<void>(
        context: context,
        builder: (BuildContext context) => MailAppPickerDialog(
          mailApps: result.options,
        ),
      );
    }

    // If no mail apps found, show error
    if (!result.didOpen && !result.canOpen) {
      Navigator.of(context).restorablePush(_showNoMailAppsDialog);

      // iOS: if multiple mail apps found, show dialog to select.
      // There is no native intent/default app system in iOS so
      // you have to do it yourself.
    } else if (!result.didOpen && result.canOpen) {
      Navigator.of(context).restorablePush(_dialogBuilder);
    }
  }

  static Route<Object?> _showNoMailAppsDialog(
      BuildContext context, Object? arguments) {
    return DialogRoute<void>(
      context: context,
      builder: (context) {
        return AlertDialog(
          title: Text("Open Mail App"),
          content: Text("No mail apps installed"),
          actions: <Widget>[
            PrimaryButton(
              title: "OK",
              onPressed: () {
                Navigator.pop(context);
              },
            )
          ],
        );
      },
    );
  }

Button(
  onPressed: () => {_openMailApp(context)},
),

  void showNoMailAppsDialog(BuildContext context) {
    showDialog<Dialog>(
      context: context,
      builder: (context) {
        return AlertDialog(
          title: Text("Open Mail App"),
          content: Text("No mail apps installed"),
          actions: <Widget>[
            TextButton(
              child: Text("OK"),
              onPressed: () {
                Navigator.pop(context);
              },
            )
          ],
        );
      },
    );
  }