动态将项目追加到ListView [英] Append items dynamically to ListView
问题描述
我是Dart和Flutter的新手,并尝试将新项目追加到我的ListView.我创建了一个递增this.value
的按钮,但没有任何反应.我是否错过了UI上的更新调用,这甚至是正确的方法吗?
由于我将ListView.builder
的值直接返回给build
的调用者,因此我不确定如何获取列表以添加更多项.非常感谢!
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:是调用setState
触发UI更新的正确方法吗?
TL;DR: Is calling setState
the correct way to trigger an UI update?
推荐答案
调用setState
是触发UI更新的正确方法.
Calling setState
is the correct way of triggering an UI update.
从文档:
调用setState通知框架 该对象的更改方式可能会影响用户界面 在此子树中,这导致框架为 这个State对象.
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.
如果您仅直接更改状态而不调用setState,则 框架可能不会安排构建,为此用户界面 子树可能不会更新以反映新状态.
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.
这是ListView
的一个小示例,其中Button
会向其附加项目.
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());
}
}
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