Je suis tombé sur cet exemple pour obtenir la taille/position d'un widget: https://medium.com/@diegoveloper/flutter-widget-size-and-position-b0a9ffed9407
quel est le problème avec mon code?
Je reçois l'erreur:
The following NoSuchMethodError was thrown while handling a gesture:
I/flutter ( 8566): The method 'findRenderObject' was called on null.
I/flutter ( 8566): Receiver: null
I/flutter ( 8566): Tried calling: findRenderObject()
void main() {
runApp(new MyApp());
}
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(home: MyWidgetSizeTMP());
}
}
class MyWidgetSizeTMP extends StatefulWidget{
@override
MyWidgetSizeTMPState createState() {
return new MyWidgetSizeTMPState();
}
}
class MyWidgetSizeTMPState extends State<MyWidgetSizeTMP> {
//creating Key for red panel
GlobalKey _keyRed = GlobalKey();
_getSizes() {
final RenderBox renderBoxRed = _keyRed.currentContext.findRenderObject();
final sizeRed = renderBoxRed.size;
print("SIZE of Red: $sizeRed");
}
_getPositions() {
final RenderBox renderBoxRed = _keyRed.currentContext.findRenderObject();
final positionRed = renderBoxRed.localToGlobal(Offset.zero);
print("POSITION of Red: $positionRed ");
}
_afterLayout(_) {
_getSizes();
_getPositions();
}
@override
void initState() {
// TODO: implement initState
super.initState();
WidgetsBinding.instance.addPostFrameCallback(_afterLayout);
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
),
body: Column(
children: <Widget>[
Flexible(
flex: 2,
child: Container(
color: Colors.red,
),
),
Flexible(
flex: 1,
child: Container(
color: Colors.purple,
),
),
Flexible(
flex: 3,
child: Container(
color: Colors.green,
),
),
Spacer(),
Padding(
padding: const EdgeInsets.only(bottom: 8.0),
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceAround,
crossAxisAlignment: CrossAxisAlignment.center,
children: <Widget>[
MaterialButton(
elevation: 5.0,
padding: EdgeInsets.all(15.0),
color: Colors.grey,
child: Text("Get Sizes"),
onPressed: _getSizes,
),
MaterialButton(
elevation: 5.0,
color: Colors.grey,
padding: EdgeInsets.all(15.0),
child: Text("Get Positions"),
onPressed: _getPositions,
)
],
),
)
],
),
);
}
}
C'est parce que le _keyRed
n'est pas attaché au contexte dans votre code.
réparer -
@override
Widget build(BuildContext context) {
return Scaffold(
key: _keyRed, //Add this.
appBar: AppBar(
Vous pouvez encapsuler dans LayoutBuilder:
return LayoutBuilder(
builder: (BuildContext context, BoxConstraints constraints) {
// height: constraints.maxHeight,
// width: constraints.maxWidth
return YourWidget();
}
);