I am still new to flutter and am learning building apps. I have been trying to run this code for but every time I run it I get a red screen on the android emulator and an error which goes "Failed Assertion: Line 22 pos 14 'url != null': is not true".
This is my main file which runs the app
import "package:flutter/material.dart";
import "src/app.dart";
voidmain() {
runApp(MyApp());
}
My App file has this code
import 'package:flutter/material.dart';
import 'package:http/http.dart' show get;
import 'models/image_models.dart';
import 'dart:convert';
import 'widgets/image_list.dart';
class MyApp extends StatefulWidget {
createState() {
return AppState();
}
}
class AppState extends State<MyApp> {
int counter = 0;
List<ImageModels> images = [];
void fetchImage() async {
counter++;
var response =
await get('http://jsonplaceholder.typicode.com/photos/$counter');
var imagemodel = ImageModels.fromjson(json.decode(response.body));
setState(() {
images.add(imagemodel);
});
}
Widget build(context) {
return MaterialApp(
home: Scaffold(
body: ImageList(images),
floatingActionButton: FloatingActionButton(
child: Icon(Icons.add),
onPressed: () {
fetchImage();
}),
appBar: AppBar(title: Text("Ola Amigo!")),
));
}
}
Heres the ImageModel Class
class ImageModels {
int id;
String url;
String title;
ImageModels(this.id, this.url, this.title);
ImageModels.fromjson(Map<String, dynamic> parsedjson) {
id = parsedjson[id];
title = parsedjson[title];
url = parsedjson[url];
}
}
and lastly the ImageList
import 'package:flutter/material.dart';
import '../models/image_models.dart';
class ImageList extends StatelessWidget {
final List<ImageModels> image;
ImageList(this.image);
Widget build(context) {
return ListView.builder(
itemCount: image.length,
itemBuilder: (context, int index) {
return buildImage(image[index]);
});
}
Widget buildImage(ImageModels image) {
return Container(
decoration: BoxDecoration(
border: Border.all(color: Colors.grey)
),
padding: EdgeInsets.all(20.0),
margin: EdgeInsets.all(20.0),
child: Image.network(image.url),
);
}
}
Can someone please take a look at it and tell me what am I doing wrong and how can I resolve this issue.
Thank you
You can copy paste run full code below
You have error in ImageModels, please revise to
code snippet
factory ImageModels.fromjson(Map<String, dynamic> parsedjson) => ImageModels(
parsedjson["id"],
parsedjson["url"],
parsedjson["title"],
);
working demo
full code
import 'dart:convert';
import 'package:http/http.dart';
import 'package:flutter/material.dart';
void main() {
runApp(MyApp());
}
class MyApp extends StatefulWidget {
createState() {
return AppState();
}
}
class AppState extends State<MyApp> {
int counter = 0;
List<ImageModels> images = [];
void fetchImage() async {
counter++;
var response =
await get('https://jsonplaceholder.typicode.com/photos/$counter');
print(response.body);
var imagemodel = ImageModels.fromjson(json.decode(response.body));
print(imagemodel.url);
setState(() {
images.add(imagemodel);
print(images[0].url);
});
}
Widget build(context) {
return MaterialApp(
home: Scaffold(
body: ImageList(images),
floatingActionButton: FloatingActionButton(
child: Icon(Icons.add),
onPressed: () {
fetchImage();
}),
appBar: AppBar(title: Text("Ola Amigo!")),
));
}
}
class ImageModels {
int id;
String url;
String title;
ImageModels(this.id, this.url, this.title);
factory ImageModels.fromjson(Map<String, dynamic> parsedjson) => ImageModels(
parsedjson["id"],
parsedjson["url"],
parsedjson["title"],
);
}
class ImageList extends StatelessWidget {
final List<ImageModels> image;
ImageList(this.image);
Widget build(context) {
return ListView.builder(
itemCount: image.length,
itemBuilder: (context, int index) {
print(image[index].url);
return buildImage(image[index]);
});
}
Widget buildImage(ImageModels image) {
return Container(
decoration: BoxDecoration(border: Border.all(color: Colors.grey)),
padding: EdgeInsets.all(20.0),
margin: EdgeInsets.all(20.0),
child: Image.network(image.url),
);
}
}
I'm facing issue to fetch json data from Flutter mobile app.
Code as follow:
import 'package:flutter/material.dart';
import 'package:flutter_app/pages/main_page.dart';
class App extends StatelessWidget
{
#override
Widget build(BuildContext context) {
return MaterialApp(
debugShowCheckedModeBanner: false,
title: "Flutter NodeJS",
home: MainPage(),
);
}
}
void main(){
runApp(App());
}
main_page.dart
import 'package:flutter/material.dart';
import 'package:flutter_app/modules/http.dart';
import 'package:flutter_app/pages/add_user_page.dart';
class MainPage extends StatefulWidget
{
#override
State<StatefulWidget> createState() {
return MainPageState();
}
}
class User
{
String id;
String first_name,email;
User(this.id, this.first_name,this.email);
}
class MainPageState extends State<MainPage>
{
List<User> users = [];
Future<void> refreshUsers()async{
var result = await http_get('users');
if(result.ok)
{
setState(() {
users.clear();
var in_users = result.data as List<dynamic>;
in_users.forEach((in_user){
users.add(User(
in_user['id'].toString(),
in_user['first_name'],
in_user['email']
));
});
});
}
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("Users"),
//email: Text("Email"),
actions: <Widget>[
IconButton(
icon: Icon(Icons.add),
onPressed: (){
Navigator.of(context).push(MaterialPageRoute(
builder: (context){
return AddUserPage();
}
));
},
)
],
),
body: RefreshIndicator(
onRefresh: refreshUsers,
child: ListView.separated(
itemCount: users.length,
itemBuilder: (context, i) => ListTile(
leading: Icon(Icons.person),
title: Text(users[i].first_name+"\n" + users[i].email),
//email: Text(users[i].email),
),
separatorBuilder: (context, i) => Divider(),
),
),
);
}
}
http.dart
import 'dart:convert';
import "package:http/http.dart" as http;
class RequestResult
{
bool ok;
dynamic data;
RequestResult(this.ok, this.data);
}
//'https://jsonplaceholder.typicode.com/users/1
//http://192.168.183.179:8081/api/users/
const PROTOCOL = "http";
const DOMAIN = "https://jsonplaceholder.typicode.com/users/1";
Future<RequestResult> http_get(String route, [dynamic data]) async
{
var dataStr = jsonEncode(data);
var url = "$PROTOCOL://$DOMAIN/$route?data=$dataStr";
var result = await http.get(url);
return RequestResult(true, jsonDecode(result.body));
}
Future<RequestResult> http_post(String route, [dynamic data]) async
{
var url = "$PROTOCOL://$DOMAIN/$route";
var dataStr = jsonEncode(data);
var result = await http.post(url, body: dataStr, headers:{"Content-Type":"application/json"});
return RequestResult(true, jsonDecode(result.body));
}
When I'm fetch json data from "https://jsonplaceholder.typicode.com/users/1". Its working fine.
enter image description here
When I try to fetch json data from "https://192.168.183.179:8081/api/users". Its give error:
at Object.createErrorWithStack (http://localhost:15340/dart_sdk.js:4348:12)
at Object._rethrow (http://localhost:15340/dart_sdk.js:37892:16)
at async._AsyncCallbackEntry.new.callback (http://localhost:15340/dart_sdk.js:37886:13)
at Object._microtaskLoop (http://localhost:15340/dart_sdk.js:37718:13)
at _startMicrotaskLoop (http://localhost:15340/dart_sdk.js:37724:13)
at http://localhost:15340/dart_sdk.js:33243:9
What I'm doing wrong
Regards,
SAO
Check in Postman whether the ip address is returning data.
Another case would be the data obtained, could not be transffered correctly to the app. Check the variables and types where the data is stored.
I tried to print in a ZEBRA ez320 Bluetooth printer I found out that it only works using cpcl code, the good news is I have the sample code for cpcl but I don't know how to integrate it on my Flutter project.
Can someone help me out?
This github https://github.com/devinim/flutter-zsdk has Zebra SDK Kit Flutter Integration
code snippet
devices = await FlutterZsdk.discoverBluetoothDevices();
devices.forEach((d) {
print('Device: ${d.friendlyName} [${d.mac}]');
});
...
d.sendZplOverBluetooth(FLUTTER_LOGO_ZPL),
full example code https://github.com/devinim/flutter-zsdk/blob/master/example/lib/main.dart
import 'package:flutter/material.dart';
import 'dart:async';
import 'package:flutter_zsdk/flutter_zsdk.dart';
void main() => runApp(MyApp());
class MyApp extends StatefulWidget {
#override
_MyAppState createState() => _MyAppState();
}
class _MyAppState extends State<MyApp> {
static const String FLUTTER_LOGO_ZPL = "^XA^CI28^PON^PW560^MNN^LL460^LH0,0^LT60" +
"^GFA,6150,6150,25,,gP01XFCgP03XF8gP07XF,gP0XFE,gO01XFC,gO03XF8,gO07XF,gO0XFE,gN01XFC,gN03XF8,gN0YF,gN0XFE,gM01XFC,gM03XF8,gM0YF,gL01XFE"
",gL01XFC,gL07XF8,gL0YF,gK01XFE,gK03XFC,gK07XF8,gK0YF,gJ01XFE,gJ03XFC,gJ07XF8,gJ0YF,gI01XFE,gI03XFC,gI07XF8,gI0YF,gH01XFE,gH03XFC,gH07XF8"
",gH0YF,gG01XFE,gG03XFC,gG07XF8,gG0YF,g01XFE,g03XFC,g07XF8,g0YF,Y01XFE,Y03XFC,Y07XF8,Y0YF,X01XFE,X03XFC,X07XF8,X0YF,W01XFE,W03XFC,W07XF8"
",W0YF,V01XFE,V03XFC,V07XF8,V0YF,U01XFE,U03XFC,U07XF8,U0YF,T01XFE,T03XFC,T07XF8,T0YF,S01XFE,S03XFC,S07XF8,S0YF,R01XFE,R03XFC,R07XF8"
",R0YF,Q01XFE,Q03XFC,Q07XF8,Q0YF,P01XFE,P03XFC,P07XF8,P0YF,O01XFE,O03XFC,O07XF8,O0YF,N01XFE,N03XFC,N07XF8,N0YF,M01XFE,M03XFC,M07XF8"
",M0YF,L01XFE,L03XFC,L07XF8,L0YF,K01XFE,K03XFC,K07XF8,K0YF,J01XFE,J03XFC,J07XF8,J0YF,I01XFE,I03XFC,I07XF8,I0XFE,001XFE,003XFCN03XF"
",007XF8N07XF,00XFEO0XFE,01XFCN01XFC,03XFCN03XF8,07XF8N07XF,0XFEO0XFE,1XFCN01XFC,3XF8N03XF8,7XF8N07XF,3WFEO0XFE,1WFCN01XFC,0WF8N03XF8"
",07VFO07XF,03UFEO0XFE,01UFCN01XFC,00UF8N03XF8,007TFO07XF,003SFEO0XFE,001SFCN01XFC,I0SF8N03XF8,I07RFO07XF,I03QFEO0XFE,I01QFCN01XFC,J0QF8N03XF8"
",J07PFO07XF,J03OFEO0XFE,J01OFCN01XFC,K0OF8N03XF8,K07NFO07XF,K03MFEO0XFE,K01MFCN01XFC,L0MF8N03XF8,L07LFO07XF,L03KFEO0XFE,L01KFCN01XFC,M0KF8N03XF8"
",M07JFO07XF,M03IFEO0XFE,M01IFCN01XFC,N0IF8N03XF8,N07FFO07XF,N03FEO0XFE,N01FCN01XFC,O0F8N03XF8,O07O07XF,O02O0XFE,X01XFC,X03XF8,X07XF,X0XFE,W01XFC"
",W03XF8,W07XF,W0XFE,V01XFC,V03XF8,V07XF,V0XFE,U01XFC,U03XF8,U07XF,U0XFE,T01XFC,T07XF8,T07XF,T03XF8,T01XFC,U0XFE,U07XF,U03XF8,U01XFC,V0XFE,V07XF"
",V03XF8,V01XFC,W0XFE,W07XF,W07XF8,W03XFC,X0XFE,X07XF,X07XF8,X03XFC,X01XFE,Y07XF,Y07XF8,Y03XFC,Y01XFE,g0YF,g07XF8,g03XFC,g01XFE,gG0YF,gG07XF8,gG03XFC"
",gG01XFE,gH0YF,gH07XF8,gH03XFC,gH01XFE,gI0YF,gI07XF8,gI03XFC,gI01XFC,gJ0XFE,gJ07XF,gJ03XF8,gJ01XFC,gK0XFE,gK07XF,gK03XF8,gK01XFC,gL0XFE,gL07XF,gL03XF8"
",gL01XFC,gM0XFE,gM07XF,gM03XF8,gM01XFC,gN0XFE,gN07XF,gN03XF8,gN01XFC,gO0XFE,gO07XF,gO03XF8,gO01XFC,gP0XFE,gP07XF,gR01VF8"
",^FS ^XZ";
List<ZebraBluetoothDevice> _devices = List();
#override
void initState() {
super.initState();
__init();
}
// Platform messages are asynchronous, so we initialize in an async method.
Future<void> __init() async {
List<ZebraBluetoothDevice> devices = List();
try {
devices = await FlutterZsdk.discoverBluetoothDevices();
devices.forEach((d) {
print('Device: ${d.friendlyName} [${d.mac}]');
});
} catch (e) {
showDialog(context: context, child: Text(e));
//throw e;
print('Error' + e);
}
if (!mounted) return;
setState(() {
_devices = devices;
});
}
String levelText = "Querying...";
_level(ZebraBluetoothDevice d) {
d.batteryLevel().then((t) {
setState(() {
levelText = t;
});
});
}
Widget _listPrinters() {
List<Widget> items = List();
if (_devices.length < 1) {
items.add(ListTile(
title: Text("Not found any or still searching"),
));
} else {
items.addAll([
ListTile(
title: Text("Found ${_devices.length} device(s)"),
),
SizedBox(height: 50),
]);
_devices.forEach((d) {
_level(d);
items.add(
ListTile(
title: Text(d.friendlyName),
subtitle: Text(d.mac + "[%${levelText}]"),
leading: IconButton(icon: Icon(Icons.list), onPressed: () => d.properties()),
trailing: IconButton(
icon: Icon(Icons.print),
onPressed: () => d.sendZplOverBluetooth(FLUTTER_LOGO_ZPL),
),
),
);
});
}
return ListView(
padding: EdgeInsets.all(24),
children: items,
);
}
#override
Widget build(BuildContext context) {
return MaterialApp(
home: Scaffold(
appBar: AppBar(
title: const Text('Zebra Plugin Example App'),
),
body: _listPrinters(),
),
);
}
}
I am looking for a way to send an API request after the user has stopped typing for X amount of seconds.
The way I am sending the request is through the onTextChanged callback, however, that sends a request on every key press
I have seen ways to do this with a timeout in React, however, I am relatively new to flutter so any help would be appreciated
you can use the below code to do this:
import 'package:flutter/material.dart';
import 'dart:async';
class Test extends StatefulWidget {
#override
State<StatefulWidget> createState() {
return _TestState();
}
}
class _TestState extends State<StatefulWidget> {
Timer searchOnStoppedTyping;
_onChangeHandler(value ) {
const duration = Duration(milliseconds:800); // set the duration that you want call search() after that.
if (searchOnStoppedTyping != null) {
setState(() => searchOnStoppedTyping.cancel()); // clear timer
}
setState(() => searchOnStoppedTyping = new Timer(duration, () => search(value)));
}
search(value) {
print('hello world from search . the value is $value');
}
#override
Widget build(BuildContext context) {
return TextField(
onChanged: _onChangeHandler,
decoration: InputDecoration(
hintText: 'Search ....'
),
);
}
}
The usual way to do this in Flutter is using RxDart and its debounce() method. It allows to wait a small period before launching a specific call.
In the following full example you see it in action with a time of 1 second. In the example, a message is shown where the call to the server should be dispatched.
import 'package:flutter/material.dart';
import 'package:rxdart/rxdart.dart';
void main() => runApp(new MyApp());
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return new MaterialApp(
home: new MyHomePage(),
);
}
}
class MyHomePage extends StatefulWidget {
#override
_MyHomePageState createState() => new _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
final subject = new PublishSubject<String>();
bool isLoading = false;
GlobalKey<ScaffoldState> scaffoldKey = new GlobalKey();
void _textChanged(String text) {
if (text.isEmpty) {
setState(() {
isLoading = false;
});
return;
}
setState(() {
isLoading = true;
});
scaffoldKey.currentState.showSnackBar(new SnackBar(
content: new Text("Search for ${text}"),
));
}
#override
void initState() {
super.initState();
subject.stream.debounce(new Duration(milliseconds: 1000)).listen(_textChanged);
}
#override
void dispose() {
subject.close();
super.dispose();
}
#override
Widget build(BuildContext context) {
return new Scaffold(
key: scaffoldKey,
appBar: new AppBar(
title: new Text("Debounce demo"),
),
body: new Container(
padding: new EdgeInsets.all(8.0),
child: new Column(
mainAxisAlignment: MainAxisAlignment.start,
children: <Widget>[
new TextField(
decoration: new InputDecoration(
hintText: 'Type text to search',
),
onChanged: (string) => (subject.add(string)),
),
isLoading
? Padding(
padding: const EdgeInsets.all(20.0),
child: new CircularProgressIndicator(),
)
: new Container(),
],
),
),
);
}
}
You can see this code in action in the following article and code by Norbert Kozsir