建设景区网站推文,电子商务网站开发流程包括,大连网站开发公司shepiguo,遵义建站1.FutureBuilder
用于处理异步操作和构建界面的非常有用的小部件。它通常与 Future 对象一起使用#xff0c;用于在异步操作完成后构建界面。
import package:flutter/material.dart;void main() runApp(MyApp());class MyApp extends StatelessWidget {overrideWidget…1.FutureBuilder
用于处理异步操作和构建界面的非常有用的小部件。它通常与 Future 对象一起使用用于在异步操作完成后构建界面。
import package:flutter/material.dart;void main() runApp(MyApp());class MyApp extends StatelessWidget {overrideWidget build(BuildContext context) {return MaterialApp(home: MyHomePage(),);}
}class MyHomePage extends StatelessWidget {FutureString fetchData() async {// 模拟异步操作例如从网络请求数据await Future.delayed(Duration(seconds: 2));return Hello, World!;}overrideWidget build(BuildContext context) {return Scaffold(appBar: AppBar(title: Text(FutureBuilder Example),),body: FutureBuilderString(future: fetchData(),builder: (BuildContext context, AsyncSnapshotString snapshot) {if (snapshot.connectionState ConnectionState.waiting) {return Center(child: CircularProgressIndicator());} else if (snapshot.hasError) {return Center(child: Text(Error: ${snapshot.error}));} else {return Center(child: Text(Data: ${snapshot.data}));}},),);}
}
如果 FutureBuilder 在构建时频繁重建可能会导致性能问题。确保不要将 FutureBuilder 嵌套在频繁重建的小部件内部以避免不必要的性能开销。
2.StreamController
要实现流式刷新通常需要使用 Stream 和 StreamBuilder 来监听和更新数据。
import dart:async;
import package:flutter/material.dart;void main() runApp(MyApp());class MyApp extends StatelessWidget {overrideWidget build(BuildContext context) {return MaterialApp(home: MyHomePage(),);}
}class MyHomePage extends StatefulWidget {override_MyHomePageState createState() _MyHomePageState();
}class _MyHomePageState extends StateMyHomePage {StreamControllerint _dataStreamController StreamControllerint();int _data 0;overridevoid initState() {super.initState();// 模拟一个数据源每秒生成一个新数据Timer.periodic(Duration(seconds: 1), (timer) {_dataStreamController.sink.add(_data);});}overridevoid dispose() {_dataStreamController.close(); // 关闭流super.dispose();}overrideWidget build(BuildContext context) {return Scaffold(appBar: AppBar(title: Text(StreamBuilder Example),),body: StreamBuilderint(stream: _dataStreamController.stream,builder: (BuildContext context, AsyncSnapshotint snapshot) {if (snapshot.connectionState ConnectionState.waiting) {return Center(child: CircularProgressIndicator());} else if (snapshot.hasError) {return Center(child: Text(Error: ${snapshot.error}));} else {return Center(child: Text(Data: ${snapshot.data}));}},),);}
}
3.ValueListenableBuilder
用于监听 ValueListenable 对象的值变化并构建界面。它允许你在值发生变化时更新界面而无需重建整个小部件树。
import package:flutter/material.dart;void main() runApp(MyApp());class CounterModel extends ValueNotifierint {CounterModel(int value) : super(value);
}class MyApp extends StatelessWidget {overrideWidget build(BuildContext context) {final counterModel CounterModel(0);return MaterialApp(home: Scaffold(appBar: AppBar(title: Text(ValueListenableBuilder Example),),body: Center(child: ValueListenableBuilderint(valueListenable: counterModel,builder: (BuildContext context, int value, Widget child) {return Column(mainAxisAlignment: MainAxisAlignment.center,children: [Text(Counter Value: $value),ElevatedButton(onPressed: () {counterModel.value;},child: Text(Increment),),],);},),),),);}
}
4.LayoutBuilder
用于获取父级小部件的约束信息并根据约束信息自定义构建界面。它通常用于创建根据父级尺寸动态调整的小部件如自适应布局。
import package:flutter/material.dart;void main() runApp(MyApp());class MyApp extends StatelessWidget {overrideWidget build(BuildContext context) {return MaterialApp(home: Scaffold(appBar: AppBar(title: Text(LayoutBuilder Example),),body: Center(child: Container(color: Colors.blue,width: 200.0,height: 200.0,child: LayoutBuilder(builder: (BuildContext context, BoxConstraints constraints) {return Center(child: Text(Width: ${constraints.maxWidth.toStringAsFixed(2)}\nHeight: ${constraints.maxHeight.toStringAsFixed(2)},style: TextStyle(color: Colors.white),),);},),),),),);}
}
5.AnimatedBuilder
用于在动画执行过程中监听值的变化并构建界面的小部件。通常它与 AnimationController 或其他动画对象一起使用以便在动画执行期间更新界面。
import package:flutter/material.dart;void main() runApp(MyApp());class MyApp extends StatelessWidget {overrideWidget build(BuildContext context) {return MaterialApp(home: Scaffold(appBar: AppBar(title: Text(AnimatedBuilder Example),),body: Center(child: MyAnimationWidget(),),),);}
}class MyAnimationWidget extends StatefulWidget {override_MyAnimationWidgetState createState() _MyAnimationWidgetState();
}class _MyAnimationWidgetState extends StateMyAnimationWidgetwith SingleTickerProviderStateMixin {AnimationController _controller;Animationdouble _animation;overridevoid initState() {super.initState();_controller AnimationController(vsync: this,duration: Duration(seconds: 2),);_animation Tween(begin: 0.0, end: 1.0).animate(_controller)..addListener(() {// 当动画值发生变化时重建界面setState(() {});});_controller.forward();}overridevoid dispose() {_controller.dispose();super.dispose();}overrideWidget build(BuildContext context) {return AnimatedBuilder(animation: _controller,builder: (BuildContext context, Widget child) {return Opacity(opacity: _animation.value,child: Container(color: Colors.blue,width: 200.0,height: 200.0,child: Center(child: Text(Opacity: ${_animation.value.toStringAsFixed(2)},style: TextStyle(color: Colors.white),),),),);},);}
}
6.PageRouteBuilder
用于自定义页面过渡动画的小部件通常与 Navigator 一起使用。它允许你创建自定义的页面切换效果包括滑动、渐变、缩放等动画效果。
import package:flutter/material.dart;void main() runApp(MyApp());class MyApp extends StatelessWidget {overrideWidget build(BuildContext context) {return MaterialApp(home: MyHomePage(),);}
}class MyHomePage extends StatelessWidget {overrideWidget build(BuildContext context) {return Scaffold(appBar: AppBar(title: Text(PageRouteBuilder Example),),body: Center(child: ElevatedButton(onPressed: () {Navigator.of(context).push(PageRouteBuilder(pageBuilder: (context, animation, secondaryAnimation) {return SecondPage();},transitionsBuilder: (context, animation, secondaryAnimation, child) {const begin Offset(1.0, 0.0);const end Offset.zero;const curve Curves.easeInOut;var tween Tween(begin: begin, end: end).chain(CurveTween(curve: curve));var offsetAnimation animation.drive(tween);return SlideTransition(position: offsetAnimation,child: child,);},),);},child: Text(Go to Second Page),),),);}
}class SecondPage extends StatelessWidget {overrideWidget build(BuildContext context) {return Scaffold(appBar: AppBar(title: Text(Second Page),),body: Center(child: ElevatedButton(onPressed: () {Navigator.of(context).pop();},child: Text(Back to First Page),),),);}
}
7.AnimatedSwitcher
用于在切换不同小部件时执行动画的小部件。它允许你在切换小部件时应用自定义的入场和出场动画效果。
import package:flutter/material.dart;void main() runApp(MyApp());class MyApp extends StatelessWidget {overrideWidget build(BuildContext context) {return MaterialApp(home: MyHomePage(),);}
}class MyHomePage extends StatefulWidget {override_MyHomePageState createState() _MyHomePageState();
}class _MyHomePageState extends StateMyHomePage {bool _showFirstWidget true;void _toggleWidget() {setState(() {_showFirstWidget !_showFirstWidget;});}overrideWidget build(BuildContext context) {return Scaffold(appBar: AppBar(title: Text(AnimatedSwitcher Example),),body: Center(child: AnimatedSwitcher(duration: Duration(milliseconds: 500), // 切换动画的持续时间child: _showFirstWidget? FirstWidget(key: ValueKeyint(1), // 指定不同的 key 以区分不同的小部件): SecondWidget(key: ValueKeyint(2), // 指定不同的 key 以区分不同的小部件),),),floatingActionButton: FloatingActionButton(onPressed: _toggleWidget,child: Icon(Icons.swap_horiz),),);}
}class FirstWidget extends StatelessWidget {FirstWidget({Key key}) : super(key: key);overrideWidget build(BuildContext context) {return Container(key: key,width: 200,height: 200,color: Colors.blue,child: Center(child: Text(First Widget,style: TextStyle(color: Colors.white),),),);}
}class SecondWidget extends StatelessWidget {SecondWidget({Key key}) : super(key: key);overrideWidget build(BuildContext context) {return Container(key: key,width: 200,height: 200,color: Colors.green,child: Center(child: Text(Second Widget,style: TextStyle(color: Colors.white),),),);}
}
8.FormBuilder
FormBuilder 是一个 Flutter 插件用于简化表单的创建和处理。它通过创建表单字段和验证逻辑让表单管理更容易。
dependencies:flutter_form_builder: ^9.1.1final GlobalKeyFormBuilderState _formKey GlobalKeyFormBuilderState();override
Widget build(BuildContext context) {return Scaffold(appBar: AppBar(title: Text(Login Form),),body: Padding(padding: const EdgeInsets.all(16.0),child: FormBuilder(key: _formKey,autovalidateMode: AutovalidateMode.always, // 自动验证模式child: Column(children: Widget[FormBuilderTextField(name: username,decoration: InputDecoration(labelText: Username),validator: FormBuilderValidators.required(context),),FormBuilderTextField(name: password,decoration: InputDecoration(labelText: Password),validator: FormBuilderValidators.required(context),),SizedBox(height: 20),ElevatedButton(onPressed: () {if (_formKey.currentState.saveAndValidate()) {// 表单验证通过执行提交操作print(_formKey.currentState.value);}},child: Text(Submit),),],),),),);
}
