您好,我尝试制作一个简单的图表,其中 x 轴为日期,Y 轴为数据。当我按下按钮时,当前日期的数据会增加。第一个目标是用下面的代码完成的。但是现在我不知道如何使图表更具动态性,我想要每个新一天的按下按钮的统计信息。我不知道如何为每个新的日子动态添加一个新的数据列。
import 'package:flutter/material.dart';
import 'package:charts_flutter/flutter.dart' as charts;
import 'package:intl/intl.dart';
void main() => runApp(new MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return new MaterialApp(
title: 'Flutter Demo',
theme: new ThemeData(
primarySwatch: Colors.blue,
),
home: new MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
@override
_MyHomePageState createState() => new _MyHomePageState();
}
class ClicksPerYear {
final String year;
final int clicks;
final charts.Color color;
ClicksPerYear(this.year, this.clicks, Color color)
: this.color = new charts.Color(
r: color.red, g: color.green, b: color.blue, a: color.alpha);
}
class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
var currentTime;
void _incrementCounter() {
setState(() {
_counter++;
});
}
@override
Widget build(BuildContext context) {
var data = [
new ClicksPerYear('2015', 3, Colors.red),
new ClicksPerYear('2016', 7, Colors.orange),
new ClicksPerYear('2017', 42, Colors.yellow),
new ClicksPerYear('$currentTime', _counter, Colors.green),
];
var series = [
new charts.Series(
domainFn: (ClicksPerYear clickData, _) => clickData.year,
measureFn: (ClicksPerYear clickData, _) => clickData.clicks,
colorFn: (ClicksPerYear clickData, _) => clickData.color,
id: 'Clicks',
data: data,
),
];
var chart = new charts.BarChart(
series,
animate: true,
);
var chartWidget = new Padding(
padding: new EdgeInsets.all(32.0),
child: new SizedBox(
height: 200.0,
child: chart,
),
);
return new Scaffold(
appBar: new AppBar(
title: new Text(widget.title),
),
body: new Center(
child: new Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
new Text(
'You have pushed the button this many times:',
),
new Text(
'$_counter',
style: Theme.of(context).textTheme.display1,
),
chartWidget,
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: () {
setState(() {
DateTime now = DateTime.now();
currentTime = DateFormat('dd/MM/yyyy').format(now);
_incrementCounter();
});
},
child: Icon(Icons.add,),
),
);
}
}
最佳答案
您分享的代码存在一些小问题。我尝试修复它们并根据您自己的代码准备更新版本。查看以下提示:
您已经使用了 Flutter 初始示例提供的计数器。此计数器是父窗口小部件的成员变量,只有一个可用的计数器。所以你必须让其他酒吧静态!这似乎不太好。将其转换为 List 或 Map 将解决它,但最好将值保存在对象本身内。
例如,假设您想在另一个页面中使用 2016 年的数据。您必须从父小部件获取数据并将其传递到新页面。但是如果你把点击保持在对象内部,你只需要传递对象本身。
data 列表在构建方法的开头定义。在这种情况下,每当小部件重建自身时,它都会启动数据列表。这似乎不太好!该列表可用,应对其应用任何更改。改进它可能会删除以前的更改。
虽然对数据变量使用 List 类型没有问题,但我建议改用 Map 类型。如果要使用 List,无论何时要对数据元素应用任何更改,都需要搜索它并找到正确的元素。但是使用 Map 类型,您可以只存储 key 并稍后使用它。
查看更正后的代码,如果您对此有任何疑问,请告诉我:
import 'package:flutter/material.dart';
import 'package:charts_flutter/flutter.dart' as charts;
import 'package:intl/intl.dart';
void main() => runApp(new MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return new MaterialApp(
title: 'Flutter Demo',
theme: new ThemeData(
primarySwatch: Colors.blue,
),
home: new MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
@override
_MyHomePageState createState() => new _MyHomePageState();
}
class ClicksPerYear {
final String year;
int clicks;
final charts.Color color;
ClicksPerYear(this.year, this.clicks, Color color)
: this.color = new charts.Color(
r: color.red, g: color.green, b: color.blue, a: color.alpha);
incrementClick() {
clicks++;
}
}
class _MyHomePageState extends State<MyHomePage> {
var currentTime = DateFormat('dd/MM/yyyy').format(DateTime.now());
Map<String, ClicksPerYear> data;
@override
void initState() {
data = {
'2015': ClicksPerYear('2015', 3, Colors.red),
'2016': ClicksPerYear('2016', 7, Colors.orange),
'2017': ClicksPerYear('2017', 42, Colors.yellow),
'$currentTime': ClicksPerYear('$currentTime', 0, Colors.green),
};
super.initState();
}
@override
Widget build(BuildContext context) {
var series = [
new charts.Series(
domainFn: (ClicksPerYear clickData, _) => clickData.year,
measureFn: (ClicksPerYear clickData, _) => clickData.clicks,
colorFn: (ClicksPerYear clickData, _) => clickData.color,
id: 'Clicks',
data: data.values.toList()),
];
var chart = new charts.BarChart(
series,
animate: true,
);
var chartWidget = new Padding(
padding: new EdgeInsets.all(32.0),
child: new SizedBox(
height: 200.0,
child: chart,
),
);
return new Scaffold(
appBar: new AppBar(
title: new Text(widget.title),
),
body: new Center(child: chartWidget),
floatingActionButton: Row(
mainAxisAlignment: MainAxisAlignment.end,
children: <Widget>[
Padding(
padding: const EdgeInsets.all(8.0),
child: FloatingActionButton(
onPressed: () {
setState(() {
data.putIfAbsent(
'2012', () => ClicksPerYear('2012', 42, Colors.teal));
});
},
child: Icon(
Icons.add,
),
backgroundColor: Colors.red,
),
),
Padding(
padding: const EdgeInsets.all(8.0),
child: FloatingActionButton(
onPressed: () {
setState(() {
DateTime now = DateTime.now();
currentTime = DateFormat('dd/MM/yyyy').format(now);
data[currentTime].incrementClick();
});
},
child: Icon(
Icons.add,
),
),
),
],
),
);
}
}
https://stackoverflow.com/questions/56040718/
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