Using showDialog in flutter is throwing error - "' !_debugLocked': is not true." - flutter

Question

I have a counter variable that is incremented every time a user opens a page. When the page is opened for 5th time I want to show a dialog. So I have used showDialog in this case. I have used showDialog inside a function. And used it in a if else short hand. In the 5th time the app is showing the following error -
'package:flutter/src/widgets/navigator.dart': Failed assertion: line 5253 pos 12: '!_debugLocked': is not true.
Here is the code-
Future<Widget> _showDialog(BuildContext c) async {
return await showDialog(
context: c,
barrierDismissible: false,
builder: (c) {
return AlertDialog(
elevation: 24.0,
backgroundColor: Colors.blue,
title: Text(
'Liking our app?',
textAlign: TextAlign.center,
style: TextStyle(
fontWeight: FontWeight.bold,
color: Colors.white,
),
),
actions: <Widget>[
TextButton(
child: Text(
"Continue as Guest",
style: TextStyle(
fontWeight: FontWeight.bold,
color: Colors.white,
),
),
onPressed: () {},
),
TextButton(
child: Text(
"Sign Up",
style: TextStyle(
fontWeight: FontWeight.bold,
color: Colors.white,
),
),
onPressed: () {},
),
],
);
});
}
Text("$_counter", textAlign: TextAlign.center),
(_counter == 5) ? _showDialog(context) : SizedBox(),

Answer 1

I had to add the following line of code before returning await showDialog(....);
await Future.delayed(Duration(seconds: 1));
And used Futurebuilder instead of directly calling the function.
(_counter == 8)
? FutureBuilder<Widget>(
future: _showDialog(context),
builder: (context, AsyncSnapshot<Widget> snap) {
if (snap.hasData) {
return snap.data;
} else {
//return CircularProgressIndicator();
return Container(height: 0.0, width: 0.0);
}
})
: Container(
height: 0.0,
width: 0.0,
),