flutter dialog prevent close

1showDialog(
2    context: context,
3    builder: (_) {
4      return AlertDialog(
5        title: Text('Wanna Exit?'),
6        actions: [
7          FlatButton(
8            onPressed: () => Navigator.pop(context, false), // passing false
9            child: Text('No'),
10          ),
11          FlatButton(
12            onPressed: () => Navigator.pop(context, true), // passing true
13            child: Text('Yes'),
14          ),
15        ],
16      );
17    }).then((exit) {
18  if (exit == null) return;
19
20  if (exit) {
21    // user pressed Yes button
22  } else {
23    // user pressed No button
24  }
25});

1showDialog(
2  barrierDismissible: false,
3  builder: ...
4)
5