I have been trying to get the size of the whole context view in Flutter. But every time I try I'm getting the above mentioned error. Here's my code:
import 'package:flutter/material.dart';
void main => runApp(new MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
final size = MediaQuery.of(context).size;
return new MaterialApp(
home: new Scaffold(),
);
}
}
Note: I also tried with a StatefulWidget
. Please, help me find what I'm doing wrong here.
You need a MaterialApp
or a WidgetsApp
around your widget. They provide the MediaQuery
. When you call .of(context)
flutter will always look up the widget tree to find the widget.
You usually have this in your main.dart:
void main() => runApp(App());
class App extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Title',
theme: kThemeData,
home: HomePage(),
);
}
}
class HomePage extends StatelessWidget {
@override
Widget build(BuildContext context) {
final size = MediaQuery.of(context).size;
return Container(
child: ...,
);
}
}
You can access MediaQuery
when you are inside MaterialApp
. The place where you are accessing the media query is not correct.
Please refer below code:
import 'package:flutter/material.dart';
class CommonThings {
static Size size;
}
void main() => runApp(new MyApp());
class MyApp extends StatelessWidget {
// This widget is the root of your application.
@override
Widget build(BuildContext context) {
return new MaterialApp(
title: 'MediaQuery Demo',
theme: new ThemeData(
primarySwatch: Colors.red,
),
home: new MyHomePage(),
);
}
}
class MyHomePage extends StatelessWidget {
@override
Widget build(BuildContext context) {
CommonThings.size = MediaQuery.of(context).size;
print('Width of the screen: ${CommonThings.size.width}');
return new Container();
}
}
I've purposely created a class CommonThings
which has static Size so that you can use it throughout the app.
I fixed it by using the following method. First I created a new class named MyWidget
and returned it in MyApp
within a MaterialApp
's home:
. Refer code below:
import 'package:flutter/material.dart';
void main => runApp(new MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return new MaterialApp(
home: new MyWidget(),
);
}
}
class MyWidget extends StatelessWidget {
@override
Widget build(BuildContext context) {
final size = MediaQuery.of(context).size;
return new MaterialApp(
home: new Scaffold(),
);
}
}
Also, declaring size as final doesn't matter. Orientation/Rotation is handled.
What works for us is using WidgetsBinding.instance.window instead of MediaQuery - also when setting the theme of the MaterialApp:
_pixelRatio = WidgetsBinding.instance.window.devicePixelRatio;
_screenWidth = WidgetsBinding.instance.window.physicalSize.width;
_screenHeight = WidgetsBinding.instance.window.physicalSize.height;
_statusBarHeight = WidgetsBinding.instance.window.padding.top;
_bottomBarHeight = WidgetsBinding.instance.window.padding.bottom;
_textScaleFactor = WidgetsBinding.instance.window.textScaleFactor;
通过重新运行应用程序解决(单击android studio中的停止按钮然后再次运行)
There is better way . Above solutions would require you to have only one screen widget or inherit all screens from parent class. But there is solution , place the media query initialization into onGenerateRoute callback function
main.dart
import 'package:flutter/material.dart';
class MyApp extends StatefulWidget {
@override
State<StatefulWidget> createState() => new MyAppState();
}
class MyAppState extends State<MyApp> {
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'My Awesome App',
routes: NavigationUtils.routeList(),
onGenerateRoute: (routeSettings) =>
NavigationUtils.onGenerateRoute(routeSettings),
);
}
}
NavigationUtils.dart
import 'package:flutter/material.dart';
class NavigationUtils {
static onGenerateRoute(RouteSettings routeSettings) {
return new MaterialPageRoute(
builder: (context) {
WidgetUtils.me.init(context);
return StorageUtils.me.isLogged() ? HomeScreen() : ForkScreen();
},
settings: routeSettings,
);
}
}
WidgetUtils.dart
import 'package:flutter/material.dart';
class WidgetUtils {
MediaQueryData _mediaQueryData;
double _screenWidth;
double _screenHeight;
double _blockSizeHorizontal;
double _blockSizeVertical;
init(BuildContext context) {
_mediaQueryData = MediaQuery.of(context);
screenWidth = _mediaQueryData.size.width;
screenHeight = _mediaQueryData.size.height;
blockSizeHorizontal = screenWidth / 100;
blockSizeVertical = screenHeight / 100;
}
}
Warning: It is not copy & paste code, there are some singletons etc. but you should get the point ;)
Had the same error in
import 'screens/tasks_screen.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return TasksScreen();
}
}
I solved it by:-
import 'package:flutter/material.dart';
import 'screens/tasks_screen.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
home: TasksScreen(),
);
}
}
Wrap your code in a Material App widget. I also had the same issue as I forgot to use it and directly returned the scaffold.
In other words, your MediaQuery.of(context) should be inside the Material Widget. Material app -> scaffold -> MediaQuery.of(context)
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
debugShowCheckedModeBanner: false,
home: MyAppOne(),
);
}
}
class MyAppOne extends StatefulWidget {
@override
_MyAppState createState() => _MyAppState();
}
class _MyAppState extends State<MyAppOne>{
@override
Widget build(BuildContext context){
return Scaffold(
);
}
}
MediaQuery
is used by Scaffold
internal components to layout its children as evident from its source code . Thus, it needs to be wrapped inside a widget which will provide a MediaQuery
, like a MaterialApp
widget, which inherits from WidgetsApp
.
To fix your MediaQuery.of(context) should be inside the Material Widget. Material app -> scaffold -> MediaQuery.of(context)
class MyApp extends StatelessWidget {
// This widget is the root of your application.
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Loading Page',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: MyAppPage(),
);
}
}
More Info: MediaQuery.of() called with a context that does not contain a MediaQuery
import 'package:flutter/material.dart';
void main() => runApp(App());
class App extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
home: Scaffold(
body:HomePage(),
),
);
}
}
class HomePage extends StatelessWidget {
@override
Widget build(BuildContext context) {
var size = MediaQuery.of(context).size.height;
return Container(
height:size/2,
color:Colors.lightBlueAccent,
);
}
}
YOU SHOULD TRY THIS I HAVE DONE IT.
I was trying to change the package then this error arise, so make sure you complete each of the following steps
添加 MaterialApp ...
void main() { runApp(MaterialApp( home: HomePage(), )); }
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