Append items dynamically to ListView - mobile

Question

I am new to Dart and Flutter and try to append a new item to my ListView. I created a button that increments this.value but nothing happens. Am I missing an update call on the UI and is this even the correct approach?
Since I return the value of ListView.builder directly to the caller of build I am not sure how to get the list to add more items. Thanks a lot!
class MyList extends State<MyList> {
...
int value = 2;
#override
Widget build(BuildContext context) {
return ListView.builder(
itemCount: this.value,
itemBuilder: (context, index) => this._buildRow(index)
);
TL;DR: Is calling setState the correct way to trigger an UI update?

Answer 1

Calling setState is the correct way of triggering an UI update.
From the docs:
Calling setState notifies the framework that the internal state of
this object has changed in a way that might impact the user interface
in this subtree, which causes the framework to schedule a build for
this State object.
If you just change the state directly without calling setState, the
framework might not schedule a build and the user interface for this
subtree might not be updated to reflect the new state.
Here is a small example of a ListView with a Button that appends items to it.
import 'package:flutter/material.dart';
void main() => runApp(new MaterialApp(home: MyList()));
class MyList extends StatefulWidget {
#override
_MyListState createState() => _MyListState();
}
class _MyListState extends State<MyList> {
int value = 2;
_addItem() {
setState(() {
value = value + 1;
});
}
#override
Widget build(BuildContext context) {
return new Scaffold(
appBar: AppBar(
title: Text("MyApp"),
),
body: ListView.builder(
itemCount: this.value,
itemBuilder: (context, index) => this._buildRow(index)),
floatingActionButton: FloatingActionButton(
onPressed: _addItem,
child: Icon(Icons.add),
),
);
}
_buildRow(int index) {
return Text("Item " + index.toString());
}
}