我正在尝试创建一个功能,当我点击FlatButton
小部件内的Expanded
时,其flex
变为2,其他兄弟姐妹FlatButton
s flex变为1。
import 'package:flutter/material.dart';
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return Directionality(
textDirection: TextDirection.ltr,
child: Column(
crossAxisAlignment: CrossAxisAlignment.stretch,
children: <Widget>[
new ButtonWidget(text: "Hello",selectedColor: Colors.yellow),
new ButtonWidget(text: "This is", selectedColor: Colors.red),
new ButtonWidget(text: "Button", selectedColor: Colors.blue),
],
),
);
}
}
class ButtonWidget extends StatefulWidget {
String text;
MaterialColor selectedColor;
ButtonWidget({this.text, this.selectedColor});
createState() =>
ButtonState(text: this.text, selectedColor: this.selectedColor);
}
class ButtonState extends State<ButtonWidget> {
String text;
MaterialColor selectedColor;
int _flexValue = 1;
ButtonState({this.text, this.selectedColor});
@override
Widget build(BuildContext context) {
return Expanded(
flex: _flexValue,
child: FlatButton(
color: selectedColor,
child: Text(
text,
),
onPressed: () {
setState(() {
_flexValue = 2;
});
},
),
);
}
}
我试图找到一种方法,也许在数组或其他东西中跟踪所有这些。我搜索并发现InheritedWidget
方法是继承的小部件,而不是兄弟姐妹。
我确信有一个干净的方法来做到这一点。但是我无法抓住它。
不要试图保持它是否在按钮本身中被选中的状态。正如您所见,很难保持3个按钮的状态同步。找到位于窗口小部件树上方的位置,您可以在该窗口中维护该状态一次。在这种情况下,它在你的应用程序中。使应用程序有状态,以便它可以记住状态,然后您的按钮不需要记住它。可以告诉他们在构造函数中是选择(大)还是未选(小)。
那么,按钮如何告诉父母它现在变成了被选中的?有各种策略,但它们都涉及:
试试这个:
import 'package:flutter/material.dart';
void main() {
runApp(MyApp());
}
class MyApp extends StatefulWidget {
@override
State createState() => MyAppState();
}
class MyAppState extends State<MyApp> {
int selected = 0;
@override
Widget build(BuildContext context) {
return Directionality(
textDirection: TextDirection.ltr,
child: Column(
crossAxisAlignment: CrossAxisAlignment.stretch,
children: <Widget>[
ButtonWidget(0, flexValue(0), 'Hello', Colors.yellow, onClick),
ButtonWidget(1, flexValue(1), 'This is', Colors.red, onClick),
ButtonWidget(2, flexValue(2), 'Button', Colors.blue, onClick),
],
),
);
}
void onClick(int i) {
setState(() {
selected = i;
});
}
int flexValue(int index) => (index == selected) ? 2 : 1;
}
class ButtonWidget extends StatelessWidget {
ButtonWidget(this.index, this._flexValue, this.text, this.selectedColor,
this.notifyClick);
final Function notifyClick;
final int index;
final int _flexValue;
final String text;
final MaterialColor selectedColor;
@override
Widget build(BuildContext context) {
return Expanded(
flex: _flexValue,
child: FlatButton(
color: selectedColor,
child: Text(
text,
),
onPressed: () {
notifyClick(index);
},
),
);
}
}
在这里你有另一种方法,将主要小部件更改为Stateful
,将按钮更改为Stateless
。
class MyApp2 extends StatefulWidget {
@override
_MyApp2State createState() => _MyApp2State();
}
class _MyApp2State extends State<MyApp2> {
int selectedIndex = -1;
onIndexChanged(int index){
setState(() {
selectedIndex = index;
});
}
@override
Widget build(BuildContext context) {
return Directionality(
textDirection: TextDirection.ltr,
child: Column(
crossAxisAlignment: CrossAxisAlignment.stretch,
children: <Widget>[
new ButtonWidget(
index: 1,
text: "Hello",
selectedColor: Colors.yellow,
selectedIndex: selectedIndex,
onChanged: onIndexChanged
),
new ButtonWidget(
index: 2,
text: "This is",
selectedColor: Colors.red,
selectedIndex: selectedIndex,
onChanged: onIndexChanged),
new ButtonWidget(
index: 3,
text: "Button",
selectedColor: Colors.blue,
selectedIndex: selectedIndex,
onChanged: onIndexChanged),
],
),
);
}
}
class ButtonWidget extends StatelessWidget {
final String text;
final MaterialColor selectedColor;
final int index;
final ValueChanged<int> onChanged;
final int selectedIndex;
ButtonWidget(
{this.text,
this.selectedColor,
this.index,
this.onChanged,
this.selectedIndex});
@override
Widget build(BuildContext context) {
return Expanded(
flex: selectedIndex != null && selectedIndex == index ? 2 : 1,
child: FlatButton(
color: selectedColor,
child: Text(
text,
),
onPressed: () => onChanged(index),
),
);
}
}