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: ...,
);
}
}
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;
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.
Solved by re-run the app(click on stop button in android studio then run again)
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(
);
}
}
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
https://stackoverflow.com/a/51550358/4993045
Add MaterialApp ...
void main() {
runApp(MaterialApp(
home: HomePage(),
));
}
Related
Here is the bloc (simplified):
import 'package:autobleidas_flutter/bloc/bloc_base.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:rxdart/rxdart.dart';
class LoginBloc extends BlocBase {
final FirebaseAuth _firebaseAuth = FirebaseAuth.instance;
final PublishSubject<bool> loggedIn = PublishSubject<bool>();
final PublishSubject<bool> loading = PublishSubject<bool>();
}
Here is the bloc provider:
class BlocProvider<T> extends InheritedWidget {
final T bloc;
BlocProvider({Key key, Widget child, this.bloc})
: super(key: key, child: child);
static T of<T extends BlocBase>(BuildContext context) {
final type = _typeOf<BlocProvider<T>>();
return (context.inheritFromWidgetOfExactType(type) as BlocProvider).bloc;
}
static Type _typeOf<T>() => T;
#override
bool updateShouldNotify(InheritedWidget oldWidget) {
return true;
}
}
However, in the LoginScreen I cannot access the loggedIn Subject of the bloc. Here is how LoginScreen is opened from main and the bloc is passed to it:
class MyApp extends StatelessWidget {
// This widget is the root of your application.
#override
Widget build(BuildContext context) {
return MaterialApp(
theme: ThemeData(
primarySwatch: Colors.blue,
),
localizationsDelegates: GlobalMaterialLocalizations.delegates,
supportedLocales: allTranslations.supportedLocales(),
home: BlocProvider<LoginBloc>(child: LoginScreen()), // <-------- HERE
);
}
}
Here is how I try to access it in the LoginScreen:
class _LoginScreenState extends State<LoginScreen> {
bool _isLoading = false;
#override
void didChangeDependencies() {
LoginBloc bloc = BlocProvider.of<LoginBloc>(context);
bloc.loggedIn.listen((isLoggedIn) => Navigator.of(context).push(
MaterialPageRoute(
builder: (BuildContext context) => RegistrationScreen())));
bloc.loading.listen((state) => setState(() => _isLoading = state));
super.didChangeDependencies();
}
#override
Widget build(BuildContext context) {
return Container();
}
the error:
The getter 'loggedIn' was called on null.
So why is the bloc null? How do I fix this?
In this line, BlocProvder expect a bloc.
home: BlocProvider<LoginBloc>(child: LoginScreen()),
You are not passing your bloc here.
Pass it like below:
home: BlocProvider<LoginBloc>(child: LoginScreen(),bloc: LoginBloc()),
BlocProvider<LoginBloc> means your defining a type of the bloc you are going to pass.
Is there any way to detect when a widget changes position? Such as when the keyboard pops up and the content is shifted up? I would like to detect this without relying on focus events or trying to detect the keyboard state.
Here's an example app:
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
home: Scaffold(
body: Center(
child: MyTextField()
)
)
);
}
}
class MyTextField extends StatelessWidget {
#override
Widget build(BuildContext context) {
return TextField();
}
}
How can you detect when MyTextField is moved up when it is focused?
You can use WidgetsBindingObserver to detect when the metrics change, here you have a sample but you will have to use GlobalKey to check the new position of your Widget :
class _MyHomePageState extends State<MyHomePage> with WidgetsBindingObserver {
GlobalKey _key = GlobalKey();
#override
void initState() {
WidgetsBinding.instance.addObserver(this);
super.initState();
}
#override
void dispose() {
WidgetsBinding.instance.removeObserver(this);
super.dispose();
}
#override
void didChangeMetrics() {
final RenderBox renderBox = _key.currentContext.findRenderObject();
final position = renderBox.localToGlobal(Offset.zero);
print("position : ${position.dx},${position.dy}");
}
#override
Widget build(BuildContext context) {
return Scaffold(
body: Center(
child: MyTextField(
key: _key,
),
),
);
}
}
class MyTextField extends StatelessWidget {
const MyTextField({Key key}) : super(key: key);
#override
Widget build(BuildContext context) {
return TextField();
}
}
If you just want to find out if the keyboard is visible, you can use this:
import 'dart:ui';
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatefulWidget {
#override
_MyAppState createState() => _MyAppState();
}
class _MyAppState extends State<MyApp> with WidgetsBindingObserver {
#override
void initState() {
super.initState();
WidgetsBinding.instance.addObserver(this);
}
#override
void dispose() {
WidgetsBinding.instance.removeObserver(this);
super.dispose();
}
#override
void didChangeMetrics() {
print('Is the keyboard visible? ${window.viewInsets.bottom != 0 ? 'yes' : 'no'}');
}
#override
Widget build(BuildContext context) {
return MaterialApp(
home: Scaffold(
body: Center(
child: TextField(),
),
),
);
}
}
Explaination: By getting the bottom position of the rectangle in which your app is drawn, you can deduce whether a system component has reduced the space of your app, hence if the keyboard is visible.
This answers only this part of your question:
Such as when the keyboard pops up and the content is shifted up?
But at least the size of the rectangle in which your app is drawn is always the current one and not an old size. This is the problem with #diegoveloper's answer, you always get the old position of the TextField.
I am trying to use GoogleTranslator library to translate input text, but i got an error that say type String is not subtype of type Widget
i tried to create a function that receive a text and return the translated text and used the widget on the body of the app
import 'package:flutter/material.dart';
import 'package:translator/translator.dart';
void main() => runApp(MyApp());
Widget translator(String input) {
GoogleTranslator translator = GoogleTranslator();
String translation = translator
.translate("I would buy a car, if I had money.", from: 'en', to: 'ar')
.toString();
return translation as Widget;
}
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
home: Scaffold(
appBar: AppBar(
title: Text('Translator'),
),
body: Center(
child: translator("Hello World"),
),
),
);
}
}
i expect the output to be in translated text in center of the screen
return translation as Widget;
should probably be
return Text(translation);
update
import 'package:flutter/material.dart';
import 'package:translator/translator.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
home: Scaffold(
appBar: AppBar(
title: Text('Translator'),
),
body: Center(
child: MyHomePage(),
),
),
);
}
}
class MyHomePage extends StatefulWidget {
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
final _translations = <String,String>{};
String translator(String input) {
if(_translations.containsKey(input)) {
return _translations[input];
} else {
_translate(input);
return input;
}
}
Future<void> _translate(String input) async {
GoogleTranslator translator = GoogleTranslator();
String translation = await translator
.translate("I would buy a car, if I had money.", from: 'en', to: 'ar');
setState(() => _translations[input] = translation);
}
#override
Widget build(BuildContext context) {
return Text(translator("Hello World"));
}
}
i was struck here while making an application my code went like this
void main() {
runApp(Myapp());
}
class Myapp extends StatelessWidget {
bool s=false;
#override
Widget build(BuildContext context) {
return (MaterialApp(
debugShowCheckedModeBanner: false,
title: "haha app",
theme: ThemeData(primarySwatch: Colors.lime),
home: s ? HomeScreen(null) : LoginPage()));
}
}
the above code is of main.dart file
and this is my another file called Login.dart and the code goes like this
class LoginPage extends StatefulWidget {
#override
_LoginPageState createState() => _LoginPageState();
}
class _LoginPageState extends State<LoginPage> {
Widget build(BuildContext context) {
return(some button ontap:(\\ on tap on this i have to change the bool s value in main.dart to true how to do that){
}
)
}
on tap the button the value s in main dart file should change to true but without navigator because we are not navigating here just a click.
please help me,
thanks in advance
You can use callbacks to communicate your widgets, like this
Create a method to get the callback , in this case : onChangeBool , pass the callback to your LoginPage Widget.
class Myapp extends StatelessWidget {
bool s=false;
onChangeBool(){
//change your var here
s = true;
//refresh the state
setState(() {
});
}
#override
Widget build(BuildContext context) {
return (MaterialApp(
debugShowCheckedModeBanner: false,
title: "haha app",
theme: ThemeData(primarySwatch: Colors.lime),
home: s ? HomeScreen(null) : LoginPage(onPressed: () => onChangeBool() ));
}
}
Receive the callBack , and call it when you press the button
class LoginPage extends StatefulWidget {
final VoidCallback onPressed;
LoginPage({this.onPressed});
#override
_LoginPageState createState() => _LoginPageState();
}
class _LoginPageState extends State<LoginPage> {
Widget build(BuildContext context) {
return RaisedButton(
child: Text("button"),
onPressed: (){
widget.onPressed();
},
)
}
)
}
In case you want to pass Data, you can use ValueChanged callback , or if you want to pass complex data, create your own callback using typedef/
A sample using ValueChanged.
class Myapp extends StatelessWidget {
bool s=false;
receiveData(String data){
print("your text here : $data");
}
#override
Widget build(BuildContext context) {
return (MaterialApp(
debugShowCheckedModeBanner: false,
title: "haha app",
theme: ThemeData(primarySwatch: Colors.lime),
home: s ? HomeScreen(null) : LoginPage(onPressed: receiveData ));
}
}
class LoginPage extends StatefulWidget {
final ValueChanged<String> onPressed;
LoginPage({this.onPressed});
#override
_LoginPageState createState() => _LoginPageState();
}
class _LoginPageState extends State<LoginPage> {
Widget build(BuildContext context) {
return RaisedButton(
child: Text("button"),
onPressed: (){
widget.onPressed("passing this data");
},
)
}
)
}
Just testing out flutter. The code sample below is a very simple flutter app. The problem is that I don't know how to call the setState() function inside the TestTextState class in order to change the text each time when the change button is pressed.
import 'package:flutter/material.dart';
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: 'Test app',
home: new Scaffold(
appBar: new AppBar(
title: new Text("Test"),
),
body: new Test(),
),
);
}
}
class Test extends StatelessWidget {
final TestText testText = new TestText();
void change() {
testText.text == "original" ? testText.set("changed") : testText.set("original");
}
#override
Widget build(BuildContext context) {
return new Column(
children: [
testText,
new RaisedButton(
child: new Text("change"),
onPressed: () => change(),
),
]
);
}
}
class TestText extends StatefulWidget {
String text = "original";
void set(String str) {
this.text = str;
}
#override
TestTextState createState() => new TestTextState();
}
class TestTextState extends State<TestText> {
#override
Widget build(BuildContext context) {
return new Text(this.widget.text);
}
}
I have approached this problem by initializing the _TestTextState as the final property of the TestText widget which allows to simply update the state when the change button is pressed. It seems like a simple solution but I'm not sure whether it's a good practice.
import 'package:flutter/material.dart';
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: 'Test app',
home: new Scaffold(
appBar: new AppBar(
title: new Text("Test"),
),
body: new Test(),
),
);
}
}
class Test extends StatelessWidget {
final _TestText text = new _TestText();
#override
Widget build(BuildContext context) {
return new Column(
children: [
text,
new RaisedButton(
child: new Text("change"),
onPressed: () => text.update(),
),
]
);
}
}
class TestText extends StatefulWidget {
final _TestTextState state = new _TestTextState();
void update() {
state.change();
}
#override
_TestTextState createState() => state;
}
class _TestTextState extends State<TestText> {
String text = "original";
void change() {
setState(() {
this.text = this.text == "original" ? "changed" : "original";
});
}
#override
Widget build(BuildContext context) {
return new Text(this.text);
}
}
thier is no way to do so. any how you have to convert your StatelessWidget to StatefulWidget.
Solution based on your existing code
class Test extends StatelessWidget {
final StreamController<String> streamController = StreamController<String>.broadcast();
#override
Widget build(BuildContext context) {
final TestText testText = TestText(streamController.stream);
return new Column(children: [
testText,
new RaisedButton(
child: Text("change"),
onPressed: () {
String text = testText.text == "original" ? "changed" : "original";
streamController.add(text);
},
),
]);
}
}
class TestText extends StatefulWidget {
TestText(this.stream);
final Stream<String> stream;
String text = "original";
#override
TestTextState createState() => new TestTextState();
}
class TestTextState extends State<TestText> {
#override
void initState() {
widget.stream.listen((str) {
setState(() {
widget.text = str;
});
});
super.initState();
}
#override
Widget build(BuildContext context) {
return Text(widget.text);
}
}
But it's not the best idea - to use non-final field inside Stateful Widget
P.S.
You can also use this - scoped_model