问题
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?
回答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());
}
}
来源:https://stackoverflow.com/questions/51343567/append-items-dynamically-to-listview