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I am fetching a data from api and display it in list using ListView builder, it's working properly on emulator but when I run app on my android phone it is displaying blank screen, here it looks.
below Leave History label, I am displaying data from api, but it looks like this now.
It looks like this on emulator
Here is the code:
Fetching api data and inserting it into list
List<leaveHistory> historyList = [];
var loader = 0;
Future<List<leaveHistory>> _getRecord() async {
Dio dio = new Dio();
var data = {
'username': getname,
'token': getaccesstoken,
};
return dio
.post(localhostUrlLeaveHistoryON, data: json.encode(data))
.then((onResponse) async {
Map<String, dynamic> map = onResponse.data;
List<dynamic> data = map["data"];
for (var historyData in data) {
leaveHistory history = leaveHistory(
historyData["Date"],
historyData["description"],
historyData["type"],
historyData['fromdate'],
historyData["todate"],
historyData["noofleavedays"],
historyData["leave"]);
historyList.add(history);
loader = 0;
}
if (historyList.length == 0) {
loader = 1;
}
return historyList;
}).catchError((onerror) {
loader = 1;
print(onerror.toString());
});
}
display the data using ListView.builder
Widget build(BuildContext context) {
return Scaffold(
appBar: new MyAppBar(
title: Text("Leaves Tracker"),
onpressed: () {
Navigator.push(
context, MaterialPageRoute(builder: (context) => Profile()));
}),
drawer: NavigationDrawerWidget(),
body: Stack(overflow: Overflow.visible, children: <Widget>[
Container(
padding: EdgeInsets.fromLTRB(20, 10, 0, 0),
child: Text(
"Leave History",
style: TextStyle(fontSize: 30, fontFamily: 'RaleWay'),
),
),
Container(
padding: EdgeInsets.fromLTRB(10, 30, 0, 0),
child: FutureBuilder(
future: _getRecord(),
builder: (BuildContext context,
AsyncSnapshot<List<leaveHistory>> snapshot) {
if (snapshot.hasData) {
if (historyList.length != 0) {
return Container(
padding: EdgeInsets.fromLTRB(0, 30, 0, 0),
child: Expanded(
child: ListView.builder(
itemCount: snapshot.data.length,
scrollDirection: Axis.vertical,
shrinkWrap: true,
itemBuilder: (BuildContext context, int index) {
Color c = Colors.red;
//changing the avatar color
if (i == 0)
i++;
else if (i == 1) {
c = Colors.blue;
i++;
} else if (i == 2) {
c = Color(int.parse(annualboxcolor));
i = 0;
}
Color c1 = Colors.green;
if (snapshot.data[index].Status == "Approved") {
c1 = Colors.green;
} else if (snapshot.data[index].Status ==
"Not Approved") {
c1 = Colors.red;
} else if (snapshot.data[index].Status ==
"Pending") {
c1 = Color(int.parse(pendingrequestcolor));
}
return SingleChildScrollView(
scrollDirection: Axis.vertical,
child: Column(
children: [
ListTile(
leading: CircleAvatar(
radius: 25,
backgroundColor: c,
child: Container(
padding: EdgeInsets.fromLTRB(
0, 10, 0, 0),
child:
Column(children: <Widget>[
Text(
snapshot
.data[index].noofdays
.toString(),
style: TextStyle(
fontSize: 15.0,
fontWeight:
FontWeight.bold,
color: Colors.white),
),
Text(
int.parse(snapshot
.data[index]
.noofdays) >
1
? "Days"
: "Day",
style: TextStyle(
fontSize: 10.0,
color: Colors.white),
)
]),
)),
title:
Text(snapshot.data[index].type),
isThreeLine: true,
subtitle: Column(
crossAxisAlignment:
CrossAxisAlignment.start,
children: [
Text(
snapshot.data[index].fromdate +
" To " +
snapshot.data[index].todate,
),
Text(snapshot.data[index].Status,
style: TextStyle(
color: c1,
fontWeight:
FontWeight.bold)),
Text(
snapshot
.data[index].description,
)
],
)),
Divider(
color: Colors.grey,
height: 10,
),
],
));
},
)));
}
}
if (loader == 1) {
print("run");
return Nodatafound();
} else {
return Center(
child: CircularProgressIndicator(
color: Colors.blue[500],
));
}
}),
),
]));
}
}
history class
class leaveHistory {
final String date;
final String fromdate;
final String todate;
final String description;
final String type;
final String Status;
final String noofdays;
leaveHistory(this.date, this.description, this.type, this.fromdate,
this.todate, this.noofdays, this.Status);
}
When i redirect to this screen from drawer it first display this error
DioError [DioErrorType.response]: Http status error [300]
on this catchError this line print(onerror.toString());
Update:
When i connect my phone with my laptop with datacable, it's working fine, but when i install apk problem occurs.
Please help where i am doing wrong.
If #Huthaifa was not the answer you're looking, have you tried to update the value of: localhostUrlLeaveHistoryON?
If you're using something like: http://localhost
Please try to change this to your computer's ip address.
Your error is caused by incorrect use of parent data widget. And that is from using expanded inside container. Remove your Expanded from here:
return Container(
padding: EdgeInsets.fromLTRB(0, 30, 0, 0),
child: Expanded(
child: ListView.builder(
You will also notice that the error in console is gone. Always read the errors and understand them. The error will 100% say, incorrect use of parent widget. Just remove the expanded.
I created an application in android studio to navigate from one screen to another.Here two stateless widgets are created as two screens and both contain a button to navigate pages each other.
However when i run the application a red screen is generated on my android phone I get an error saying
exception 'Column's children must not contain any null values, but a null value was found at index 0'.
I have provided my code below:
FIRST SCREEN
class FirstScreen extends StatelessWidget {
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("First Screen"),
),
body: Container(
child: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
center(
decoration: new BoxDecoration(
image: new DecorationImage(
image: new AssetImage('assets/new 7wonders.jpg'),
fit: BoxFit.cover,
),
),
),
Text('New 7 Wonders',
style: TextStyle(fontSize: 40, fontStyle: FontStyle.italic),
),
RaisedButton(
child: Text("Bang Here"),
onPressed: (){
Navigator.push(context, MaterialPageRoute(builder: (context) => SecondScreen()));
},
color: Colors.red,
textColor: Colors.yellow,
padding: EdgeInsets.fromLTRB(10, 10, 10, 10),
splashColor: Colors.grey,
)
],
),
),
),
);
}
center({BoxDecoration decoration}) {}
}
SECOND SCREEN
class SecondScreen extends StatelessWidget {
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("Second Screen"),
),
body: RaisedButton(
child: Text("Go to First page"),
onPressed:() {
Navigator.pop(context);
},
),
);
}
}
Your center method should return a Widget, it is currently providing null to the Column.
Do this instead:
Widget center() {
// return a decorated box widget which gives you the decoration property
return Image(
image: AssetImage(
'assets/new 7wonders.jpg',),
fit: BoxFit.cover,
);
}
}
Then use in your Column like :
Container(
child: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
// call the center method which returns a Widget
center(),
Text(
'New 7 Wonders',
style: TextStyle(fontSize: 40, fontStyle: FontStyle.italic),
),
RaisedButton(
child: Text("Bang Here"),
onPressed: () {
Navigator.push(context,
MaterialPageRoute(builder: (context) => SecondScreen()));
},
color: Colors.red,
textColor: Colors.yellow,
padding: EdgeInsets.fromLTRB(10, 10, 10, 10),
splashColor: Colors.grey,
)
],
),
),
),
you have to return any widget in center
center({BoxDecoration decoration}) {
return Container();
}
You tryed write Center instead center in line 24?
And in Center must be will return for example Containter()
In 24th line, you returned null value. You can implement the center method like this;
return Container();
Remove center use this
Container(
height: 100, // height and width according to your ui
width:100,
child:Image.asset(('assets/new7wonders.jpg',fit: BoxFit.cover,), // use for local image from asset and please change image name in code as well as in asset folder.there should not be space between image name .
),
I have been experimenting with Flutter trying to recreate an app that I wrote for Android 5 years ago. But I can't seem to get the layout to work very well.
I have tried a number of different widgets, but each time I try something, it seems like I am taking 2 steps forward and 3 steps back.
The app is going to be vertical position only.
Simple banner image at the top.
A trivia question.
Radio button group with 4 answers.
Then 2 buttons - 'Check Answer' and 'Skip Question'
Bottom bar
I am trying to make sure that the radio buttons and the buttons don't bounce around when the question changes.
This is what I have
This is what I would like
And this is the code that I have been fighting with.
Any help or tips would be greatly appreciated.
class _MyHomePageState extends State<MyHomePage> {
final TriviaBloc _triviaBloc = TriviaBloc();
TriviaQuestion _initTriviaQuestion = new TriviaQuestion('', '', '', '', '', 1, 1);
String _selectedAnswer = "";
TextStyle _answerStyle = new TextStyle(textBaseline: TextBaseline.alphabetic, fontStyle: FontStyle.normal, fontFamily: 'QarmicsansAbridged', fontSize: 16);
#override
void dispose() {
_triviaBloc.dispose();
super.dispose();
}
#override
void initState() {
super.initState();
}
#override
Widget build(BuildContext context) {
return Scaffold(
backgroundColor: Colors.orangeAccent,
body: SafeArea(
minimum: const EdgeInsets.all(16.0),
child:
Column(children: [
ImageBanner("assets/header_2.jpg"),
Expanded(
child:
StreamBuilder<TriviaQuestion>(
initialData: _triviaBloc.getInitialTriviaQuestion(),
//_initTriviaQuestion,
stream: _triviaBloc.triviaQuestionStream,
//initialData: _triviaBloc.getInitialTriviaQuestion(),
//builder: (BuildContext context, AsyncSnapshot<TriviaQuestion> snapshot)
builder: (BuildContext context, snapshot) {
//_triviaBloc.getTriviaQuestion(snapshot, context);
if (snapshot.data != null) {
return Column(
crossAxisAlignment: CrossAxisAlignment.center,
mainAxisSize: MainAxisSize.min,
children: <Widget>[
SizedBox(height: 15),
Padding(
padding: EdgeInsets.all(2.0),
child: TriviaAutoSizeText(context, snapshot.data.Question),
),
RadioButtonGroup(
labels: <String>[
snapshot.data.IncorrectAnswer1,
snapshot.data.IncorrectAnswer2,
snapshot.data.CorrectAnswer,
snapshot.data.IncorrectAnswer3
],
labelStyle: _answerStyle,
onSelected: (String selected) => _selectedAnswer = selected),
//),
SizedBox(height: 10),
new InkWell(
onTap: () => {_triviaBloc.checkAnswer(QuestionAnswered(_selectedAnswer))},
child: new Container(
width: MediaQuery.of(context).size.width * 0.5,
height: 50.0,
decoration: new BoxDecoration(
color: _butttonInteriorColour,
//Colors.blueAccent,
border:
new Border.all(color: Colors.white, width: 1.0),
borderRadius: new BorderRadius.circular(20.0),
),
child: new Center(
child: new Text(
'Check Answer',
style: new TextStyle(
fontSize: 18.0, color: Colors.white),
),
),
),
),
SizedBox(height: 10),
new InkWell(
onTap: () =>
{_triviaBloc.getTriviaQuestion(snapshot, context)},
child: new Container(
width: MediaQuery.of(context).size.width * 0.5,
height: 50.0,
decoration: new BoxDecoration(
color: _butttonInteriorColour,
//Colors.blueAccent,
border:
new Border.all(color: Colors.white, width: 1.0),
borderRadius: new BorderRadius.circular(20.0),
),
child: new Center(
child: new Text(
'Next Question',
style: new TextStyle(
fontSize: 18.0, color: Colors.white),
),
),
),
),
],
);
} else {
return Center(child: CircularProgressIndicator());
}
;
}),
)]),
),
bottomNavigationBar: buildBottomNav(context),
);
}
}
So you want the 4 button group and the 2 buttons at the bottom without changing position ?
Maybe a Spacer will help with that
if (snapshot.data != null) {
return Column(
crossAxisAlignment: CrossAxisAlignment.center,
mainAxisSize: MainAxisSize.max, //replace this to fill everything
children: <Widget>[
SizedBox(height: 15),
Padding(
padding: EdgeInsets.all(2.0),
child: TriviaAutoSizeText(context, snapshot.data.Question),
),
Spacer(), //add the spacer here
RadioButtonGroup(
labels: <String>[
My problem is that : The listview does not appear at the first launch of app but after a hot reload it appears.
It's the first time I meet this bug.
That's my code :
#override
Widget build(BuildContext context) {
return new Scaffold(
backgroundColor: Colors.black,
body: new ListView.builder(
itemCount: toutesLesCartes.length,
itemBuilder: (context, count) {
Carte carte = toutesLesCartes[count];
String nom = carte.nomCarte;
String image = carte.imageCarte;
return new Dismissible(
key: new Key(nom),
direction: DismissDirection.endToStart,
child: new Container(
margin: EdgeInsets.all(5.0),
child: new Card(
color: Colors.transparent,
elevation: 10.0,
child: new Row(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
mainAxisSize: MainAxisSize.min,
children: <Widget>[
new Image.network(image, width: 150.0, height: 150.0,),
new CustomText(nom, factor: 2.0,),
],
),
),
),
background: new Container(
padding: EdgeInsets.only(right: 20.0),
color: Colors.red,
child: new Row(
mainAxisAlignment: MainAxisAlignment.end,
children: <Widget>[
new CustomText("Supprimer"),
new Icon(Icons.delete, color: Colors.white,)
],
),
),
onDismissed: (direction) {
setState(() {
toutesLesCartes.removeAt(count);
nombreCarteChoisiValeur--;
});
},
);
}
),
);
}
I have an idea but it's strange : before, I using the Visibility widget so it is possible that it comes from a possible "cache" of the application?
All that will look at this post and help me, thank you very much!
Have a nice day !
Likely because toutesLesCartes.length is 0.
you can check this using the debugger or display something when the length is 0 eg
#override
Widget build(BuildContext context) {
return new Scaffold(
backgroundColor: Colors.black,
body: new ListView.builder(
itemCount: toutesLesCartes.length, //* place breakpoint here
itemBuilder: (context, count) {
Carte carte = toutesLesCartes[count];
String nom = carte.nomCarte;
String image = carte.imageCarte;
if(toutesLesCartes == null || toutesLesCartes.length == 0){
return CircularProgressIndicator(); //you should see loading animation if list is empty
}
return new Dismissible(
key: new Key(nom),
direction: DismissDirection.endToStart,
child: new Container(
margin: EdgeInsets.all(5.0),
child: new Card(
color: Colors.transparent,
elevation: 10.0,
child: new Row(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
mainAxisSize: MainAxisSize.min,
children: <Widget>[
new Image.network(image, width: 150.0, height: 150.0,),
new CustomText(nom, factor: 2.0,),
],
),
),
),
background: new Container(
padding: EdgeInsets.only(right: 20.0),
color: Colors.red,
child: new Row(
mainAxisAlignment: MainAxisAlignment.end,
children: <Widget>[
new CustomText("Supprimer"),
new Icon(Icons.delete, color: Colors.white,)
],
),
),
onDismissed: (direction) {
setState(() {
toutesLesCartes.removeAt(count);
nombreCarteChoisiValeur--;
});
},
);
}
),
);
}
The solution would be to use a FutureBuilder
Word of warning: The application will run the build method multiple times, it's good practice to place anything you don't want to be repeatedly called (like database calls) outside of the method.
I have a long text and I need to show the scrollbar by default when the user enters my page.
Currently, the bars not shown until the user click over the text and this, not good behavior because the user could leave the page without notice that there is some unread text.
My code:
return Scaffold(
body: Padding(
padding: const EdgeInsets.all(15.0),
child: Center(
child: Column(
children: <Widget>[
Image.asset(
"assets/images/logo.png",
height: 200.0,
),
SizedBox(
height: 40,
),
Expanded(
child: Scrollbar(
child: SingleChildScrollView(
child: Text("Long Text Here ...",
textDirection: TextDirection.rtl,
style: TextStyle(fontSize: 17.2),
),
),
),
),
SizedBox(
height: 50,
),
Row(
children: <Widget>[
Expanded(
child: RaisedButton(
child: Text("Continue"),
onPressed: () {
MaterialPageRoute route = MaterialPageRoute(
builder: (BuildContext context) => MainPage());
Navigator.of(context).push(route);
},
),
),
SizedBox(
width: 20.0,
),
RaisedButton(
child: Text("Close"),
onPressed: () {
exit(0);
},
),
],
)
],
),
),
),
);
}```
As of Flutter version 1.17, on Scrollbar you can set isAlwaysShown to true, but you must set the same controller for your Scrollbar and your SingleChildScrollView (and that applies to any other scrollable Widget as well).
Have in mind that, for the Scrollbar to be visible, there must be enough items to scroll. If there are not, the Scrollbar won't be shown.
Full working example:
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
home: Scaffold(
body: MyWidget(),
),
);
}
}
class MyWidget extends StatefulWidget {
#override
_MyWidgetState createState() => _MyWidgetState();
}
class _MyWidgetState extends State<MyWidget> {
final _scrollController = ScrollController();
#override
Widget build(BuildContext context) {
return Scaffold(
body: Padding(
padding: const EdgeInsets.all(15.0),
child: Center(
child: Column(
children: <Widget>[
// ...
Expanded(
child: Scrollbar(
controller: _scrollController, // <---- Here, the controller
isAlwaysShown: true, // <---- Required
child: SingleChildScrollView(
controller: _scrollController, // <---- Same as the Scrollbar controller
child: Text(
"Long Text Here ...",
textDirection: TextDirection.rtl,
style: TextStyle(fontSize: 17.2),
),
),
),
),
// ...
],
),
),
),
);
}
}
As of v2.9.0-1.0, thumbVisiblity is the proper field to set.
Note you can set this globally for your app (or a certain subtree) using ScrollbarTheme:
return MaterialApp(
...
theme: ThemeData(
...
scrollbarTheme: ScrollbarThemeData(
thumbVisibility: MaterialStateProperty.all<bool>(true),
)
)
)
It's good to prefer themes for styling like this, so avoid doing more than once.
You'll still need to add a Scrollbar and Controller as described in other answers though.
Use draggable_scrollbar package. It provides a dragable scrollbar with option to make the scrollbar always visible. For example, you can use the following code
DraggableScrollbar.arrows(
alwaysVisibleScrollThumb: true, //use this to make scroll thumb always visible
labelTextBuilder: (double offset) => Text("${offset ~/ 100}"),
controller: myScrollController,
child: ListView.builder(
controller: myScrollController,
itemCount: 1000,
itemExtent: 100.0,
itemBuilder: (context, index) {
return Container(
padding: EdgeInsets.all(8.0),
child: Material(
elevation: 4.0,
borderRadius: BorderRadius.circular(4.0),
color: Colors.purple[index % 9 * 100],
child: Center(
child: Text(index.toString()),
),
),
);
},
),
);
'isAlwaysShown' is deprecated and shouldn't be used. Use thumbVisibility instead.
Example:
Scrollbar(
controller: ScrollController(),
thumbVisibility: true,
child: SingleChildScrollView(
child: Column(
thumbVisibility make true for show always scroll bar for list in scrollbar widget
Scrollbar(thumbVisibility: true,)
You can change the scrollbartheme to set flag isAlwaysShown true
scrollbarTheme: const ScrollbarThemeData(isAlwaysShown: true)