这里的问题是,在按下按钮更改 funArg 值后,Container 不会重绘自身,该按钮应该更改其高度,因为它已用于计算
代码如下:
这里是 main.dart:
import 'package:flutter/material.dart';
import 'package:sqaure/ui/fun.dart';
Widget rect0;
String rectArg = "20";
class Home extends StatefulWidget {
@override
State<StatefulWidget> createState() {
return new HomeState();
}
}
class HomeState extends State<Home> {
var list = ["20", "15"];
Widget funTest() {
setState(() {
rectArg = list[1];
rect0 = new Plate(rectArg);
});
}
//final Color primaryColor = Colors.red;
@override
Widget build(BuildContext context) {
return new Scaffold(
appBar: new AppBar(
title: new Text("rect"),
backgroundColor: Colors.red,
),
body: Column(
mainAxisAlignment: MainAxisAlignment.start,
children: <Widget>[
new Container(
alignment: Alignment.topCenter,
color: Colors.white,
height: 245.0,
child: new Stack(
children: <Widget>[
Center(
child: Padding(
padding: const EdgeInsets.only(left: 55.0),
child: Row(
children: <Widget>[
//plates
rect0 = new Plate(rectArg),
],
),
),
)
],
),
),
new RaisedButton(onPressed: () {
funTest();
debugPrint(rectArg);
})
],
),
);
}
}
这里是 fun.dart:
import 'package:flutter/material.dart';
class Plate extends StatefulWidget {
final String funArg2;
@override
State<StatefulWidget> createState() {
return new PlateState(funArg2);
}
[enter image description here][1]
Plate(this.funArg2);
}
class PlateState extends State<Plate> {
String funArg;
@override
Widget build(BuildContext context) {
return Padding(
padding: const EdgeInsets.all(3.0),
child: Container(
alignment: Alignment.center,
color: Colors.redAccent,
height: funArg != "" ? (9.33 * double.parse(funArg) + 45) : 0.0,
width: 29.0,
child: new Text(
funArg,
style: new TextStyle(
color: Colors.white,
fontWeight: FontWeight.w600,
fontSize: funArg.length > 4
? 10.0
: funArg.length > 3 ? 14.0 : 19.0,
),
),
));
}
PlateState(this.funArg);
}
如您所见,容器的高度由内部的子文本决定。
谢谢。
最佳答案
这是您的代码的固定注释版本。请阅读评论!
主要问题是您将 Plate
定义为有状态的小部件,并将 rectArg
存储在该状态中! PlateState
只启动一次,直到你离开屏幕,它不会在父部件重建时重新创建!
Plate
实际上没有任何内部状态,所以它应该是一个 StatelessWidget
。你应该总是喜欢 StatelessWidget
。理解为什么是 Flutter 开发的基础!
import 'package:flutter/material.dart';
main() => runApp(MaterialApp(home: Home()));
class Home extends StatefulWidget {
@override
State<StatefulWidget> createState() {
return new HomeState();
}
}
// this seems to be a constant, so can put it outside of the class
// or alternatively inside, with "static const" modifier
const list = ["20", "15"];
class HomeState extends State<Home> {
// stateful variables (things that change over time)
// must be inside of your state class
String rectArg = "20";
// we can return void here!
void funTest() {
setState(() {
// state is modified here. this triggers a rebuild/redraw
// that means the build function is called again
// note that we are only the storing the string value, NOT a widget!
rectArg = list[1];
});
}
// this is called every time you setState
@override
Widget build(BuildContext context) {
return new Scaffold(
appBar: new AppBar(
title: new Text("rect"),
backgroundColor: Colors.red,
),
body: Column(
mainAxisAlignment: MainAxisAlignment.start,
children: <Widget>[
new Container(
alignment: Alignment.topCenter,
color: Colors.white,
height: 245.0,
child: new Stack(
children: <Widget>[
Center(
child: Padding(
padding: const EdgeInsets.only(left: 55.0),
child: Row(
children: <Widget>[
// DO NOT SET VARIABLES FROM THE BUILD METHOD!
// this is bad:
// rect0 = new Plate(rectArg),
Plate(
funArg: rectArg,
),
],
),
),
)
],
),
),
new RaisedButton(onPressed: () {
funTest();
debugPrint(rectArg);
})
],
),
);
}
}
// Plate is actually a StatelessWidget because it is not interactive and holds no internal state
// All the data (funArg) is passed in from the parent ==> StatelessWidget
// Always prefer stateless widgets!
// That means the widget is completely rebuilt every time the build() method is called in HomeState
class Plate extends StatelessWidget {
// Use named constructor parameters and call the super constructor!
// you can auto-generate the constructor with Android Studio
const Plate({Key key, this.funArg}) : super(key: key);
final String funArg;
Widget build(BuildContext context) {
return Padding(
padding: const EdgeInsets.all(3.0),
child: Container(
alignment: Alignment.center,
color: Colors.redAccent,
height: funArg != "" ? (9.33 * double.parse(funArg) + 45) : 0.0,
width: 29.0,
child: new Text(
funArg,
style: new TextStyle(
color: Colors.white,
fontWeight: FontWeight.w600,
fontSize: funArg.length > 4 ? 10.0 : funArg.length > 3 ? 14.0 : 19.0,
),
),
),
);
}
}
以防万一您需要一个具有内部状态的 StatefulWidget
,它也具有由父小部件设置的构造函数参数(这很常见):在 build
方法中您的 State
,使用 widget
属性访问您的小部件的最终字段:
class ColoredCheckbox extends StatefulWidget {
const ColoredCheckbox({Key key, this.color}) : super(key: key);
// this is passed in from the parent, can change when the parent is rebuilt
final Color color;
@override
State<StatefulWidget> createState() => ColoredCheckboxState();
}
class ColoredCheckboxState extends State<ColoredCheckbox> {
// this is internal state, kept even when the parent is rebuilt
bool checked = false;
// build is called when:
// - you call setState from this widget
// - when the parent widget is rebuilt
@override
Widget build(BuildContext context) {
return RaisedButton(
child: Text(checked ? 'X' : '0'),
// use "widget" to access the fields passed in from the parent
color: widget.color,
onPressed: () {
// always call setState when changing internal state
setState(() {
checked = !checked;
});
},
);
}
}
关于android - Flutter:按下按钮时更改容器的高度,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/51598255/