error_navigator

//File lib/main.dart

import 'package:flutter/material.dart';
import 'package:sanca_news/single_article.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
          // backgroundColor: Colors.green,
          appBar: AppBar(
        ...
        ...
          ),
          body: Padding(
            padding: const EdgeInsets.all(10.0),
            child: ListView(
              children: <Widget>[
                // card for newest articles
                Card(
            ...
            ...
                ),

                Container(
            ...
            ...
            ...
                ),

                buildCard(),
                buildCard(),
                buildCard(),
                buildCard(),
                buildCard(),
              ],
            ),
          )),
    );
  }

  String text =
      "Ini text beritanya Ini text beritanya Ini text beritanya Ini text ...";

  Card buildCard() {
    return Card(
      shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(10)),
      elevation: 5,
      child: Row(
        mainAxisAlignment: MainAxisAlignment.spaceAround,
        children: [
          Flexible(
              flex: 2,
              child: Container(
                  margin: EdgeInsets.all(5),
                  child: Column(
                    crossAxisAlignment: CrossAxisAlignment.start,
                    children: [
                      Text(
                        text,
                        style: TextStyle(
                            fontSize: 12,
                            fontWeight: FontWeight.w700,
                            fontFamily: "Poppins"),
                      ),
                      Container(
                        margin: EdgeInsets.only(top: 5),
                        child: RaisedButton(
                          onPressed: () {
                            Navigator.push(
                                context,
                                MaterialPageRoute(
                                    builder: (BuildContext context) =>
                                        SingleArticle()));
                          },
                          child: Text(
                            "Read more ...",
                            style: TextStyle(fontFamily: "Poppins"),
                          ),
                        ),
                      )
                    ],
                  ))),
          Flexible(
        ...
        ...
        ),
        ],
      ),
    );
  }
}



//File single_article.dart
import 'package:flutter/material.dart';

class SingleArticle extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text("Halaman Single Article"),
        ),
        body: Center(
          child: Text("Halaman Single Article"),
        ),
      ),
    );
  }
}


//Error yang muncul:

══╡ EXCEPTION CAUGHT BY GESTURE ╞═══════════════════════════════════════════════════════════════════
The following assertion was thrown while handling a gesture:
Navigator operation requested with a context that does not include a Navigator.
The context used to push or pop routes from the Navigator must be that of a widget that is a
descendant of a Navigator widget.
When the exception was thrown, this was the stack:
...
...

(elided 3 frames from dart:async)
Handler: "onTap"
Recognizer:
  TapGestureRecognizer#e04f5

═══════ Exception caught by gesture ═══════════════════════════════════════════
The following assertion was thrown while handling a gesture:
Navigator operation requested with a context that does not include a Navigator.

...
...