我正在开发一个flutter应用程序,需要在其中扫描一些条形码,因此,为此,我使用了一个名为barcode_scan(https://pub.dartlang.org/packages/barcode_scan)的插件。 因此,当我尝试从存储在步骤列表中的RaisedButton调用函数时会出现问题,因为当我在onPressed Android Studio上调用初始化条形码扫描器的函数时,我需要在Stepper小部件中显示该按钮显示此消息“只能在初始化程序中访问静态成员”。
初始化条形码扫描器的功能:
Future scan() async {
try {
String barcode = await BarcodeScanner.scan();
setState(() => this.barcode = barcode);
} on PlatformException catch (e) {
if (e.code == BarcodeScanner.CameraAccessDenied) {
setState(() {
this.barcode = 'The user did not grant the camera permission!';
});
} else {
setState(() => this.barcode = 'Unknown error: $e');
}
} on FormatException{
setState(() => this.barcode = 'null (User returned using the "back"-button before scanning anything. Result)');
} catch (e) {
setState(() => this.barcode = 'Unknown error: $e');
}}
以及“步骤列表”的代码
List<Step> mySteps = [
new Step(title: new Text("Scan first"),
content: new Column(
children: <Widget>[
new Text("Code"),
new Container(
padding: EdgeInsets.only(top: 20),
child: new Text("A08B",style: TextStyle(
fontSize: 30,
color: Colors.red
),
)
,),
new Container(
child: new RaisedButton(onPressed: scan ,
child: new Text("Scan"),),
)
],
))];
全飞镖类:
void main() => runApp(MaterialApp(
home: Ubicacion(),
));
class Ubicacion extends StatefulWidget {
@override
_UbicacionState createState() => _UbicacionState();}
class _UbicacionState extends State<Ubicacion> {
String barcode = "";
Future scan() async {
try {
String barcode = await BarcodeScanner.scan();
setState(() => this.barcode = barcode);
} on PlatformException catch (e) {
if (e.code == BarcodeScanner.CameraAccessDenied) {
setState(() {
this.barcode = 'The user did not grant the camera permission!';
});
} else {
setState(() => this.barcode = 'Unknown error: $e');
}
} on FormatException{
setState(() => this.barcode = 'null (User returned using the "back"-button before scanning anything. Result)');
} catch (e) {
setState(() => this.barcode = 'Unknown error: $e');
}
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('hello'),
),
body: Container(
padding: EdgeInsets.all(32.0),
child: Center(
child: Column(
children: <Widget>[
new Container(
child: new Stepper(steps: mySteps,
currentStep: this.pasoActual,
onStepContinue: (){
setState(() {
if(pasoActual <mySteps.length -1){
pasoActual++;
}else{
pasoActual = 0;
}
});
},
onStepCancel: (){
setState(() {
if(pasoActual >0){
pasoActual--;
}else{
pasoActual = 0;
}
});
},),
)
],
),
),
),
);
}
int pasoActual = 0;
List<Step> mySteps = [
new Step(title: new Text("Escanear palet"),
content: new Column(
children: <Widget>[
new Text("Codigo"),
new Text("ID",),
new Text("PLU"),
new Container(
padding: EdgeInsets.only(top: 20),
child: new Text("A08B",style: TextStyle(
fontSize: 30,
color: Colors.red
),
)
,),
new Container(
child: new RaisedButton(onPressed: null ,
child: new Text("Escanear"),),
)
],
))
];
}
答案 0 :(得分:0)
当您在类中声明非静态变量时尝试直接对其进行初始化时,会发生上述错误。
对于您的情况,我假设这是您直接初始化的mySteps
列表。
如果使用initState()
或在类构造函数中,请尝试在Stateful Widget
方法中对其进行初始化,并且错误将消失。
您也可以查看this答案以获取有关同一问题的详细说明。