超过百万的StackOverflow Flutter 问题

Wrap(
  children: <Widget>[your_child])

Container(
        height: double.infinity,width: double.infinity,child:your_child)

Row(
  mainAxisSize: MainAxisSize.max,children: <Widget>[*your_child*],);

Column(
  mainAxisSize: MainAxisSize.max,children: <Widget>[your_child],);

@override
Widget build(BuildContext context) {
  return FutureBuilder(
    future: httpCall(),builder: (context,snapshot) {
     
    },);
}

class _ExampleState extends State<Example> {
  Future<int> future;

  @override
  void initState() {
    future = Future.value(42);
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return FutureBuilder(
      future: future,snapshot) {
       
      },);
  }
}

Widget _currentBody;

@override
Widget build(BuildContext context) {
  return Scaffold(
    body: _currentBody,bottomNavigationBar: BottomNavigationBar(
      items: <BottomNavigationBarItem>[
      	...
      ],onTap: (index) {
        _bottomNavigationChange(index);
      },),);
}

_bottomNavigationChange(int index) {
  switch (index) {
    case 0:
      _currentBody = OnePage();
      break;
    case 1:
      _currentBody = TwoPage();
      break;
    case 2:
      _currentBody = ThreePage();
      break;
  }
  setState(() {});
}

int _currIndex;

@override
Widget build(BuildContext context) {
  return Scaffold(
    body: IndexedStack(
        index: _currIndex,children: <Widget>[OnePage(),TwoPage(),ThreePage()],);
}

_bottomNavigationChange(int index) {
  setState(() {
      _currIndex = index;
    });
}

TabBarView(
  controller: this._tabController,children: <Widget>[
    _buildTabView1(),_buildTabView2(),],)

var _newsKey = PageStorageKey('news');
var _technologyKey = PageStorageKey('technology');

TabBarView(
  controller: this._tabController,children: <Widget>[
    _buildTabView1(_newsKey),_buildTabView2(_technologyKey),)

Center(
  child: Container(
    height: 300,width: 300,color: Colors.blue,child: Stack(
      children: <Widget>[
        Positioned.fill(
          child: Container(
            height: 100,width: 100,color: Colors.red,)
      ],)

Positioned.fill(
  child: Align(
    child: Container(
      height: 100,)

class Test extends StatefulWidget {
  Test({this.data});
  final int data;
  @override
  State<StatefulWidget> createState() => _TestState();
}

class _TestState extends State<Test>{

}

1. 在_TestState也定义同样的参数，此方式比较麻烦，不推荐。
2. 直接使用widget.data（推荐）。

class BarrageItem extends StatefulWidget {
  BarrageItem(
      { this.text,this.duration = Duration(seconds: 3)});

const Duration _kDuration = Duration(seconds: 3);

class BarrageItem extends StatefulWidget {
  BarrageItem(
      {this.text,this.duration = _kDuration});

MaterialApp(
 debugShowCheckedModeBanner: false
)

Color(0xb74093)

Color(0xFFb74093)

class _FooState extends State<Foo> {
  TextEditingController _controller;

  @override
  void initState() {
    super.initState();
    _controller = new TextEditingController(text: '初始值');
  }

  @override
  Widget build(BuildContext context) {
    return TextField(
          controller: _controller,);
  }
}

class HomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('老孟'),body: Center(
        child: RaisedButton(
          color: Colors.pink,textColor: Colors.white,onPressed: _displaySnackBar(context),child: Text('show SnackBar'),);
  }
}

_displaySnackBar(BuildContext context) {
  final snackBar = SnackBar(content: Text('老孟'));
  Scaffold.of(context).showSnackBar(snackBar);
}

_scaffoldKey.currentState.showSnackBar(snackbar); 

Scaffold(
    appBar: AppBar(
        title: Text('老孟'),body: Builder(
        builder: (context) => 
            Center(
            child: RaisedButton(
            color: Colors.pink,onPressed: () => _displaySnackBar(context),child: Text('老孟'),);

killall -9 dart

taskkill /F /IM dart.exe

MediaQuery.of(context).size.width * 0.5

Row(
	children: <Widget>[
		Flexible(
			child: new TextField(),

FocusScope.of(context).requestFocus(_focusNode);

_focusNode = FocusNode();

TextField(
	focusNode: _focusNode,...
)

_focusNode.unfocus();

import 'dart:io' show Platform;

if (Platform.isAndroid) {
  // Android-specific code
} else if (Platform.isIOS) {
  // iOS-specific code
}

Platform.isAndroid
Platform.isFuchsia
Platform.isIOS
Platform.isLinux
Platform.isMacOS
Platform.isWindows

<?xml version="1.0" encoding="utf-8"?>
<manifest ... >
    <application android:networkSecurityConfig="@xml/network_security_config">
		 <!-- ... -->
    </application>
</manifest>

<?xml version="1.0" encoding="utf-8"?>
<network-security-config>
    <base-config cleartextTrafficPermitted="true">
        <trust-anchors>
            <certificates src="system" />
        </trust-anchors>
    </base-config>
</network-security-config>

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
	...
	<key>NSAppTransportSecurity</key>
	<dict>
		<key>NSAllowsArbitraryLoads</key>
		<true/>
	</dict>
</dict>
</plist>