Accessing variables out of scope - dart

Question

I am trying to navigate to a new page newData[index]["title"] when tap on listTile, how can I access newData, index and data variables out of this scope, I know I have to declare them in global scope but I tried this.index, but it doesn't work, I created a _onTap() method but I don't have access to index so I can only access the by asking for a specific position [0] for instance.
class _ContentPageState extends State<ContentPage> {
#override
Widget build(BuildContext context,) {
List data;
return new Scaffold(
appBar: new AppBar(
title: new Text("Local json file"),
),
body: new Container(
child: new Center(
child: new FutureBuilder(
future: DefaultAssetBundle
.of(context)
.loadString('data_files/file.json'),
builder: (context, snapshot) {
var newData = JSON.decode(snapshot.data.toString());
return new ListView.builder(
itemBuilder: (BuildContext context, int index) {
return new Card(
child: new ListTile(
title: new Text(newData[index]['title'],textScaleFactor: 1.5),
),
);
},
itemCount: newData == null ? 0 : newData.length,
);
}),
),
));
}
}

Answer 1

I guess you're trying to have a private _onTap method inside your class similar to :
_onTap(newData, int index) {
}
That's pretty simple, inside your ListTile you can wrap your _onTap inside another function like this :
return new Card(
child: new ListTile(
onTap: () => _onTap(newData, index),
title: new Text(newData[index]['title'], textScaleFactor: 1.5),
),
);

Answer 2

the previous answer is passing newData as argument. Another alternative is declare newData outside the build method.
class _ContentPageState extends State<ContentPage> {
var newData;// << here >> after class
#override
Widget build(BuildContext context,) {
So, in the assign remove de type (var)
newData = JSON.decode(snapshot.data.toString());