[بالأرصفة] رفرفة. الجزء 5. لمطوري Xamarin.Forms

المحتوى:

1. مشروع
   
   • ?
   • Page Element?
   
   
2. Views
   
   • ? XAML-?
   • ?
   • ?
   • ?
   • ?
   • ?
   
   
3. 
   
   • ?
   • ?
   
   
4. Async UI
   
   • Device.BeginInvokeOnMainThread()? ?
   • ?
   • ?
   
   
5. 
   
   • ?
   • ? ?
   • ?
   
   
6. 
   
   • ?
   
   
7. Layouts
   
   • StackLayout?
   • Grid?
   • ScrollView?
   
   
8. 
   
   • ?
   • ?
   
   
9. ListView
   
   • ListView?
   • كيفية تحديد العنصر الذي تم النقر عليه؟
   • كيفية تحديث ListView بشكل حيوي؟
   
   
10. نص
    
    • كيفية استخدام الخطوط المخصصة؟
    • كيفية تصميم الحاجيات النصية؟
    • ما هو المكافئ للعنصر النائب؟
    • كيفية إظهار أخطاء التحقق من الصحة؟
    
    
11. الإضافات Flutter
    
    • كيفية الوصول إلى GPS؟
    • كيفية الوصول إلى الكاميرا؟
    • كيفية تسجيل الدخول عبر Facebook؟
    • كيفية استخدام Firebase؟
    
    
12. رمز خاص بالنظام الأساسي
    
    • كيفية تحديد النظام الأساسي الذي تعمل عليه الشفرة؟
    • كيفية استدعاء رمز النظام الأساسي الأصلي؟
    
    
13. تصحيح الأخطاء
    
    • ما هي أدوات تصحيح التطبيق؟
    • كيفية جعل إعادة التحميل الساخنة؟
    • كيفية الوصول إلى قائمة المطور في التطبيق؟
    
    
14. التخزين المحلي
    
    • كيفية تخزين بيانات القيمة الرئيسية في تطبيق؟
    • كيفية تخزين البيانات المعقدة؟
    
    

مشروع

سؤال:

إجابة:

اختلافات:

مثال:

void main() {
  runApp(new MyApp());
}

سؤال:

إجابة:

اختلافات:

مثال:

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter Demo',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        // Take the value from the MyHomePage object that was created by
        // the App.build method, and use it to set the appbar title.
        title: new Text(widget.title),
      ),
      body: new Center(
        // Center is a layout widget. It takes a single child and positions it
        // in the middle of the parent.
        child: new Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            new Text(
              'You have pushed the button this many times:',
            ),
            new Text(
              '$_counter',
              style: Theme.of(context).textTheme.display1,
            ),
          ],
        ),
      ),
      floatingActionButton: new FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: new Icon(Icons.add),
      ),
    );
  }
}

الآراء

سؤال:

إجابة:

فرق:

معلومة اضافية:

مثال:

@override
Widget build(BuildContext context) {
  return new Scaffold(
    appBar: new AppBar(
      title: new Text("Sample App"),
    ),
    body: new Center(
      child: new MaterialButton(
        onPressed: () {},
        child: new Text('Hello'),
        padding: new EdgeInsets.only(left: 10.0, right: 10.0),
      ),
    ),
  );
}

سؤال:

إجابة:

اختلافات:

مثال:

class SampleApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Sample App',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new SampleAppPage(),
    );
  }
}

class SampleAppPage extends StatefulWidget {
  SampleAppPage({Key key}) : super(key: key);

  @override
  _SampleAppPageState createState() => new _SampleAppPageState();
}

class _SampleAppPageState extends State<SampleAppPage> {
  // Default value for toggle
  bool toggle = true;
  void _toggle() {
    setState(() {
      toggle = !toggle;
    });
  }

  _getToggleChild() {
    if (toggle) {
      return new Text('Toggle One');
    } else {
      return new CupertinoButton(
        onPressed: () {},
        child: new Text('Toggle Two'),
      );
    }
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text("Sample App"),
      ),
      body: new Center(
        child: _getToggleChild(),
      ),
      floatingActionButton: new FloatingActionButton(
        onPressed: _toggle,
        tooltip: 'Update Text',
        child: new Icon(Icons.update),
      ),
    );
  }
}

سؤال:

إجابة:

اختلافات:

معلومة اضافية:

مثال:

import 'package:flutter/material.dart';

void main() {
  runApp(new FadeAppTest());
}

class FadeAppTest extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Fade Demo',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new MyFadeTest(title: 'Fade Demo'),
    );
  }
}

class MyFadeTest extends StatefulWidget {
  MyFadeTest({Key key, this.title}) : super(key: key);
  final String title;
  @override
  _MyFadeTest createState() => new _MyFadeTest();
}

class _MyFadeTest extends State<MyFadeTest> with TickerProviderStateMixin {
  AnimationController controller;
  CurvedAnimation curve;

  @override
  void initState() {
    controller = new AnimationController(duration: const Duration(milliseconds: 2000), vsync: this);
    curve = new CurvedAnimation(parent: controller, curve: Curves.easeIn);
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text(widget.title),
      ),
      body: new Center(
          child: new Container(
              child: new FadeTransition(
                  opacity: curve,
                  child: new FlutterLogo(
                    size: 100.0,
                  )))),
      floatingActionButton: new FloatingActionButton(
        tooltip: 'Fade',
        child: new Icon(Icons.brush),
        onPressed: () {
          controller.forward();
        },
      ),
    );
  }
}

سؤال:

إجابة:

اختلافات:

مثال:

import 'package:flutter/material.dart';

void main() => runApp(new MaterialApp(home: new DemoApp()));

class DemoApp extends StatelessWidget {
  Widget build(BuildContext context) => new Scaffold(body: new Signature());
}

class Signature extends StatefulWidget {
  SignatureState createState() => new SignatureState();
}

class SignatureState extends State<Signature> {
  List<Offset> _points = <Offset>[];
  Widget build(BuildContext context) {
    return new GestureDetector(
      onPanUpdate: (DragUpdateDetails details) {
        setState(() {
          RenderBox referenceBox = context.findRenderObject();
          Offset localPosition =
          referenceBox.globalToLocal(details.globalPosition);
          _points = new List.from(_points)..add(localPosition);
        });
      },
      onPanEnd: (DragEndDetails details) => _points.add(null),
      child: new CustomPaint(painter: new SignaturePainter(_points), size: Size.infinite),
    );
  }
}

class SignaturePainter extends CustomPainter {
  SignaturePainter(this.points);
  final List<Offset> points;
  void paint(Canvas canvas, Size size) {
    var paint = new Paint()
      ..color = Colors.black
      ..strokeCap = StrokeCap.round
      ..strokeWidth = 5.0;
    for (int i = 0; i < points.length - 1; i++) {
      if (points[i] != null && points[i + 1] != null)
        canvas.drawLine(points[i], points[i + 1], paint);
    }
  }
  bool shouldRepaint(SignaturePainter other) => other.points != points;
}

سؤال:

إجابة:

اختلافات:

سؤال:

إجابة:

اختلافات:

مثال:

class CustomButton extends StatelessWidget {
  final String label;

  CustomButton(this.label);

  @override
  Widget build(BuildContext context) {
    return new RaisedButton(onPressed: () {}, child: new Text(label));
  }
}

التنقل

سؤال:

إجابة:

اختلافات:

1. تعيين الأسماء لوصف الطريق ؛
2. انتقل مباشرة إلى المسار .

مثال:

void main() {
  runApp(CupertinoApp(
    home: MyAppHome(), // becomes the route named '/'
    routes: <String, WidgetBuilder> {
      '/a': (BuildContext context) => MyPage(title: 'page A'),
      '/b': (BuildContext context) => MyPage(title: 'page B'),
      '/c': (BuildContext context) => MyPage(title: 'page C'),
    },
  ));
}

Navigator.of(context).pushNamed('/b');

سؤال:

إجابة:

واجهة مستخدم غير متزامنة

سؤال:

إجابة:

مثال:

loadData() async {
  String dataURL = "https://jsonplaceholder.typicode.com/posts";
  http.Response response = await http.get(dataURL);
  setState(() {
    widgets = json.decode(response.body);
  });
}

import 'dart:convert';

import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;

void main() {
  runApp(SampleApp());
}

class SampleApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Sample App',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: SampleAppPage(),
    );
  }
}

class SampleAppPage extends StatefulWidget {
  SampleAppPage({Key key}) : super(key: key);

  @override
  _SampleAppPageState createState() => _SampleAppPageState();
}

class _SampleAppPageState extends State<SampleAppPage> {
  List widgets = [];

  @override
  void initState() {
    super.initState();

    loadData();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Sample App"),
      ),
      body: ListView.builder(
          itemCount: widgets.length,
          itemBuilder: (BuildContext context, int position) {
            return getRow(position);
          }));
  }

  Widget getRow(int i) {
    return Padding(
      padding: EdgeInsets.all(10.0),
      child: Text("Row ${widgets[i]["title"]}")
    );
  }

  loadData() async {
    String dataURL = "https://jsonplaceholder.typicode.com/posts";
    http.Response response = await http.get(dataURL);
    setState(() {
      widgets = json.decode(response.body);
    });
  }
}

سؤال:

إجابة:

مثال:

dependencies:
  ...
  http: ^0.11.3+16

import 'dart:convert';

import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
[...]
  loadData() async {
    String dataURL = "https://jsonplaceholder.typicode.com/posts";
    http.Response response = await http.get(dataURL);
    setState(() {
      widgets = json.decode(response.body);
    });
  }
}

سؤال:

إجابة:

اختلافات:

مثال:

import 'dart:convert';

import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;

void main() {
  runApp(new SampleApp());
}

class SampleApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Sample App',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new SampleAppPage(),
    );
  }
}

class SampleAppPage extends StatefulWidget {
  SampleAppPage({Key key}) : super(key: key);

  @override
  _SampleAppPageState createState() => new _SampleAppPageState();
}

class _SampleAppPageState extends State<SampleAppPage> {
  List widgets = [];

  @override
  void initState() {
    super.initState();
    loadData();
  }

  showLoadingDialog() {
    return widgets.length == 0;
  }

  getBody() {
    if (showLoadingDialog()) {
      return getProgressDialog();
    } else {
      return getListView();
    }
  }

  getProgressDialog() {
    return new Center(child: new CircularProgressIndicator());
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
        appBar: new AppBar(
          title: new Text("Sample App"),
        ),
        body: getBody());
  }

  ListView getListView() => new ListView.builder(
      itemCount: widgets.length,
      itemBuilder: (BuildContext context, int position) {
        return getRow(position);
      });

  Widget getRow(int i) {
    return new Padding(padding: new EdgeInsets.all(10.0), child: new Text("Row ${widgets[i]["title"]}"));
  }

  loadData() async {
    String dataURL = "https://jsonplaceholder.typicode.com/posts";
    http.Response response = await http.get(dataURL);
    setState(() {
      widgets = json.decode(response.body);
    });
  }
}

هيكل المشروع والموارد

سؤال:

إجابة:

اختلافات:

معلومة اضافية:

images/my_icon.png       // Base: 1.0x image
images/2.0x/my_icon.png  // 2.0x image
images/3.0x/my_icon.png  // 3.0x image

assets:
 - images/my_icon.jpeg

return AssetImage("images/a_dot_burr.jpeg");

@override
Widget build(BuildContext context) {
  return Image.asset("images/my_image.png");
}

سؤال:

إجابة:

اختلافات:

مثال:

class Strings {
  static String welcomeMessage = "Welcome To Flutter";
}

new Text(Strings.welcomeMessage)

dependencies:
  # ...
  flutter_localizations:
    sdk: flutter
  intl: "^0.15.6"

import 'package:flutter_localizations/flutter_localizations.dart';

new MaterialApp(
 localizationsDelegates: [
   // Add app-specific localization delegate[s] here.
   GlobalMaterialLocalizations.delegate,
   GlobalWidgetsLocalizations.delegate,
 ],
 supportedLocales: [
    const Locale('en', 'US'), // English
    const Locale('he', 'IL'), // Hebrew
    // ... other locales the app supports
  ],
  // ...
)

سؤال:

إجابة:

دورة حياة التطبيق

سؤال:

إجابة:

معلومة اضافية:

• غير نشط - هذه الطريقة موجودة فقط في iOS ، ولا يوجد في Android نظير ؛
• متوقف مؤقتًا - مشابهًا لـ onPause () في Android ؛
• تم الاستئناف - على غرار onPostResume () في Android ؛
• تعليق - على غرار onStop في Android ، في iOS لا يوجد تناظرية.

مثال:

import 'package:flutter/widgets.dart';

class LifecycleWatcher extends StatefulWidget {
  @override
  _LifecycleWatcherState createState() => _LifecycleWatcherState();
}

class _LifecycleWatcherState extends State<LifecycleWatcher> with WidgetsBindingObserver {
  AppLifecycleState _lastLifecycleState;

  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addObserver(this);
  }

  @override
  void dispose() {
    WidgetsBinding.instance.removeObserver(this);
    super.dispose();
  }

  @override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    setState(() {
      _lastLifecycleState = state;
    });
  }

  @override
  Widget build(BuildContext context) {
    if (_lastLifecycleState == null)
      return Text('This widget has not observed any lifecycle changes.', textDirection: TextDirection.ltr);

    return Text('The most recent lifecycle state this widget observed was: $_lastLifecycleState.',
        textDirection: TextDirection.ltr);
  }
}

void main() {
  runApp(Center(child: LifecycleWatcher()));
}

التخطيطات

سؤال:

إجابة:

مثال:

@override
Widget build(BuildContext context) {
  return new Column(
    mainAxisAlignment: MainAxisAlignment.center,
    children: <Widget>[
      new Text('Column One'),
      new Text('Column Two'),
      new Text('Column Three'),
      new Text('Column Four'),
    ],
  );
}

@override
Widget build(BuildContext context) {
  return new Row(
    mainAxisAlignment: MainAxisAlignment.center,
    children: <Widget>[
      new Text('Row One'),
      new Text('Row Two'),
      new Text('Row Three'),
      new Text('Row Four'),
    ],
  );
}

سؤال:

إجابة:

مثال:

GridView.count(
  // Create a grid with 2 columns. If you change the scrollDirection to
  // horizontal, this would produce 2 rows.
  crossAxisCount: 2,
  // Generate 100 widgets that display their index in the List
  children: List.generate(100, (index) {
    return Center(
      child: Text(
        'Item $index',
        style: Theme.of(context).textTheme.headline,
      ),
    );
  }),
);

سؤال:

إجابة:

مثال:

@override
Widget build(BuildContext context) {
  return new SingleChildScrollView(
    child: new Text('Long Content'),
  );
}

@override
Widget build(BuildContext context) {
  return new ListView(
    children: <Widget>[
      new Text('Row One'),
      new Text('Row Two'),
      new Text('Row Three'),
      new Text('Row Four'),
    ],
  );
}

التعامل مع الإيماءات

سؤال:

إجابة:

مثال:

@override
Widget build(BuildContext context) {
  return new RaisedButton(
      onPressed: () {
        print("click");
      },
      child: new Text("Button"));
}

class SampleApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
        body: new Center(
      child: new GestureDetector(
        child: new FlutterLogo(
          size: 200.0,
        ),
        onTap: () {
          print("tap");
        },
      ),
    ));
  }
}

سؤال:

إجابة:

صنبور

• onTapDown
• onTapUp
• يراقب حركاته
• onTapCancel

انقر مرّتين

• onDoubleTap

ضغطة طويلة

• onLongPress

سحب عمودي

• onVerticalDragStart
• onVerticalDragUpdate
• onVerticalDragEnd

السحب الأفقي

• onHorizontalDragStart
• onHorizontalDragUpdate
• onHorizontalDragEnd

مثال:

AnimationController controller;
CurvedAnimation curve;

@override
void initState() {
  controller = new AnimationController(duration: const Duration(milliseconds: 2000), vsync: this);
  curve = new CurvedAnimation(parent: controller, curve: Curves.easeIn);
}

class SampleApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
        body: new Center(
          child: new GestureDetector(
            child: new RotationTransition(
                turns: curve,
                child: new FlutterLogo(
                  size: 200.0,
                )),
            onDoubleTap: () {
              if (controller.isCompleted) {
                controller.reverse();
              } else {
                controller.forward();
              }
            },
        ),
    ));
  }
}

ListView والمحولات

سؤال:

إجابة:

اختلافات:

مثال:

import 'package:flutter/material.dart';

void main() {
  runApp(new SampleApp());
}

class SampleApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Sample App',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new SampleAppPage(),
    );
  }
}

class SampleAppPage extends StatefulWidget {
  SampleAppPage({Key key}) : super(key: key);

  @override
  _SampleAppPageState createState() => new _SampleAppPageState();
}

class _SampleAppPageState extends State<SampleAppPage> {
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text("Sample App"),
      ),
      body: new ListView(children: _getListData()),
    );
  }

  _getListData() {
    List<Widget> widgets = [];
    for (int i = 0; i < 100; i++) {
      widgets.add(new Padding(padding: new EdgeInsets.all(10.0), child: new Text("Row $i")));
    }
    return widgets;
  }
}

سؤال:

إجابة:

اختلافات:

مثال:

import 'package:flutter/material.dart';

void main() {
  runApp(new SampleApp());
}

class SampleApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Sample App',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new SampleAppPage(),
    );
  }
}

class SampleAppPage extends StatefulWidget {
  SampleAppPage({Key key}) : super(key: key);

  @override
  _SampleAppPageState createState() => new _SampleAppPageState();
}

class _SampleAppPageState extends State<SampleAppPage> {
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text("Sample App"),
      ),
      body: new ListView(children: _getListData()),
    );
  }

  _getListData() {
    List<Widget> widgets = [];
    for (int i = 0; i < 100; i++) {
      widgets.add(new GestureDetector(
        child: new Padding(
            padding: new EdgeInsets.all(10.0),
            child: new Text("Row $i")),
        onTap: () {
          print('row tapped');
        },
      ));
    }
    return widgets;
  }
}

سؤال:

إجابة:

اختلافات:

مثال:

import 'package:flutter/material.dart';

void main() {
  runApp(SampleApp());
}

class SampleApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Sample App',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: SampleAppPage(),
    );
  }
}

class SampleAppPage extends StatefulWidget {
  SampleAppPage({Key key}) : super(key: key);

  @override
  _SampleAppPageState createState() => _SampleAppPageState();
}

class _SampleAppPageState extends State<SampleAppPage> {
  List widgets = [];

  @override
  void initState() {
    super.initState();
    for (int i = 0; i < 100; i++) {
      widgets.add(getRow(i));
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Sample App"),
      ),
      body: ListView(children: widgets),
    );
  }

  Widget getRow(int i) {
    return GestureDetector(
      child: Padding(
        padding: EdgeInsets.all(10.0),
        child: Text("Row $i"),
      ),
      onTap: () {
        setState(() {
          widgets = List.from(widgets);
          widgets.add(getRow(widgets.length + 1));
          print('row $i');
        });
      },
    );
  }
}

معلومة اضافية:

مثال:

import 'package:flutter/material.dart';

void main() {
  runApp(SampleApp());
}

class SampleApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Sample App',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: SampleAppPage(),
    );
  }
}

class SampleAppPage extends StatefulWidget {
  SampleAppPage({Key key}) : super(key: key);

  @override
  _SampleAppPageState createState() => _SampleAppPageState();
}

class _SampleAppPageState extends State<SampleAppPage> {
  List widgets = [];

  @override
  void initState() {
    super.initState();
    for (int i = 0; i < 100; i++) {
      widgets.add(getRow(i));
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Sample App"),
      ),
      body: ListView.builder(
        itemCount: widgets.length,
        itemBuilder: (BuildContext context, int position) {
          return getRow(position);
        },
      ),
    );
  }

  Widget getRow(int i) {
    return GestureDetector(
      child: Padding(
        padding: EdgeInsets.all(10.0),
        child: Text("Row $i"),
      ),
      onTap: () {
        setState(() {
          widgets.add(getRow(widgets.length + 1));
          print('row $i');
        });
      },
    );
  }
}

نص

سؤال:

إجابة:

مثال:

fonts:
   - family: MyCustomFont
     fonts:
       - asset: fonts/MyCustomFont.ttf
       - style: italic

@override
Widget build(BuildContext context) {
  return Scaffold(
    appBar: AppBar(
      title: Text("Sample App"),
    ),
    body: Center(
      child: Text(
        'This is a custom font text',
        style: TextStyle(fontFamily: 'MyCustomFont'),
      ),
    ),
  );
}

سؤال:

إجابة:

• اللون؛
• زخرفة؛
• الزخرفة
• الديكور
• خط العائلة؛
• حجم الخط؛
• نوع الخط؛
• الوزن
• رمز التجزئة ؛
• ارتفاع؛
• يرث؛
• letterSpacing ؛
• النص الأساسي ؛
• تباعد الكلمات.

سؤال:

إجابة:

مثال:

body: new Center(
  child: new TextField(
    decoration: new InputDecoration(hintText: "This is a hint"),
  )
)

سؤال:

إجابة:

مثال:

class SampleApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Sample App',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: SampleAppPage(),
    );
  }
}

class SampleAppPage extends StatefulWidget {
  SampleAppPage({Key key}) : super(key: key);

  @override
  _SampleAppPageState createState() => _SampleAppPageState();
}

class _SampleAppPageState extends State<SampleAppPage> {
  String _errorText;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Sample App"),
      ),
      body: Center(
        child: TextField(
          onSubmitted: (String text) {
            setState(() {
              if (!isEmail(text)) {
                _errorText = 'Error: This is not an email';
              } else {
                _errorText = null;
              }
            });
          },
          decoration: InputDecoration(hintText: "This is a hint", errorText: _getErrorText()),
        ),
      ),
    );
  }

  _getErrorText() {
    return _errorText;
  }

  bool isEmail(String emailString) {
    String emailRegexp =
        r'^(([^<>()[\]\\.,;:\s@\"]+(\.[^<>()[\]\\.,;:\s@\"]+)*)|(\".+\"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$';

    RegExp regExp = RegExp(emailRegexp);

    return regExp.hasMatch(emailString);
  }
}

الإضافات Flutter

سؤال:

إجابة:

سؤال:

إجابة:

سؤال:

إجابة:

سؤال:

إجابة:

• firebase_admob لـ Firebase AdMob ؛
• firebase_analytics لـ Firebase Analytics ؛
• firebase_auth لـ Firebase Auth ؛
• firebase_database لFirebase RTDB.
• firebase_storage لـ Firebase Cloud Storage ؛
• firebase_messaging لمراسلة Firebase (FCM) ؛
• flutter_firebase_ui للتكامل السريع لـ Firebase Auth (Facebook و Google و Twitter والبريد الإلكتروني) ؛
• cloud_firestore ل Firebase Cloud Firestore.

رمز خاص بالنظام الأساسي

سؤال:

إجابة:

مثال:

if (Theme.of(context).platform == TargetPlatform.iOS) {
  return 'iOS';
} else if (Theme.of(context).platform == TargetPlatform.android) {
  return 'android';
} else if (Theme.of(context).platform == TargetPlatform.fuchsia) {
  return 'fuchsia';
} else {
  return 'not recognised ';
}

if (Platform.isIOS) {
  return 'iOS';
} else if (Platform.isAndroid) {
  return 'android';
} else if (Platform.isFuchsia) {
  return 'fuchsia';
} else {
  return 'not recognised ';
}

سؤال:

إجابة:

معلومة اضافية:

تصحيح الأخطاء

سؤال:

إجابة:

سؤال:

إجابة:

سؤال:

إجابة:

معلومة اضافية:

التخزين المحلي

سؤال:

إجابة:

اختلافات:

مثال:

dependencies:
  flutter:
    sdk: flutter
  shared_preferences: ^0.4.3

SharedPreferences prefs = await SharedPreferences.getInstance();
_counter = prefs.getInt('counter');
prefs.setInt('counter', ++_counter);
setState(() {
  _counter = _counter;
});

سؤال:

إجابة: