我正在努力使用 GlobalKey 获取小部件的高度,但是在渲染布局后调用获取高度的函数以确保上下文可用时,key.currentState 和 key.currentContext 仍然返回 null。
import 'package:flutter/material.dart';
class TestPage extends StatefulWidget{
@override
State<StatefulWidget> createState() => new TestPageState();
}
class TestPageState extends State<TestPage>{
final TestWidget testWidget = new TestWidget();
@override
initState() {
//calling the getHeight Function after the Layout is Rendered
WidgetsBinding.instance
.addPostFrameCallback((_) => getHeight());
super.initState();
}
void getHeight(){
final GlobalKey key = testWidget.key;
//returns null:
final State state = key.currentState;
//returns null:
final BuildContext context = key.currentContext;
//Error: The getter 'context' was called on null.
final RenderBox box = state.context.findRenderObject();
print(box.size.height);
print(context.size.height);
}
@override
Widget build(BuildContext context) {
return new Scaffold(
body: testWidget,
);
}
}
class TestWidget extends StatefulWidget{
@override
Key get key => new GlobalKey<TestWidgetState>();
@override
State<StatefulWidget> createState() => new TestWidgetState();
}
class TestWidgetState extends State<TestWidget>{
@override
Widget build(BuildContext context) {
return new Container(
child: new Text("Test", style: const TextStyle(fontSize: 32.0, fontWeight: FontWeight.bold),),
);
}
}
runApp(TestPage());
运行它,它将返回此错误,但是如果您在TestPage中包装MediaQuery和Directionality小部件(提供数据和textDirection参数),或者使用MaterialApp或WidgetsApp小部件,它应该可以运行(至少对我来说是这样)。 - userManyNumbers