我是 Flutter 的新手。
我有非常簡單的應用程式
主要飛鏢：
import 'package:dart_test/views/widgets/items/pack_items.dart';
import 'package:dart_test/views/widgets/items/pack_row.dart';
import 'package:flutter/material.dart';
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
print("app build");
var pdata =
PackData(packId: 'npack1', name: 'Pack1', name_ru: 'пак 1', nImages: 5);
//print("~w:$contW");
return MaterialApp(
home: PackBody(data: pdata, offset: 0).build(context));
}
}
PackBody.dart：
class PackBody extends ListItem {
final PackData data;
final int offset;
PackBody({required this.data, required this.offset});
@override
Widget build(BuildContext context) {
var ar = 896.0 / 768;
//var contWidth=MediaQuery.of(context).size.width;
return Container(
width: MediaQuery.of(context).size.width,
height: 50,
child: Text('khkljgkjhgkjhg'),
);
}
}
它拋出了一個例外：
我試圖PackBody用MediaQuery- 不走運
不應該MaterialApp提供MediaQuery給層次結構？
Upd：我誤解了問題的核心。正確的模式應該是：
void main() {
runApp(MaterialApp(home:MyApp()));
}
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return //your widget
}
uj5u.com熱心網友回復：
你在做什么和寫一樣：
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
print("app build");
var pdata = PackData(packId: 'npack1', name: 'Pack1', name_ru: 'пак 1', nImages: 5);
//print("~w:$contW");
return MaterialApp(
home: Container(
width: MediaQuery.of(context).size.width,
height: 50,
child: Text('khkljgkjhgkjhg'),
),
);
}
}
小MediaQuery部件建立一個子樹，媒體查詢在其中決議給定資料。MaterialApp引入 aMediaQuery并在當前螢屏指標發生變化時使其保持最新。為了MediaQuery.of(context)作業，它需要在那個子樹中，從我之前提供的代碼示例中，它顯然不是。更新：在下面添加完整示例
import 'package:flutter/material.dart';
void main() {
runApp(const MyApp());
}
class MyApp extends StatelessWidget {
const MyApp({Key? key}) : super(key: key);
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Demo',
theme: ThemeData(
primarySwatch: Colors.red,
),
home: const MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
const MyHomePage({Key? key, required this.title}) : super(key: key);
final String title;
@override
State<MyHomePage> createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Text(
MediaQuery.of(context).size.height.toString(),
),
);
}
}
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