import'package:flutter/material.dart';voidmain(){runApp(newMaterialApp(title:'Flutter Tutorial',home:newTutorialHome(),));}// 这里创建的为一个无状态的widgetclassTutorialHomeextendsStatelessWidget{@overrideWidgetbuild(BuildContextcontext){//Scaffold是Material中主要的布局组件.returnnewScaffold(appBar:newAp...
crossAxisAlignment: CrossAxisAlignment.stretch, children: <Widget>[ Expanded( flex: 1, child: Container( color: Colors.blue, ), ), Expanded( flex: 2, child: getMyPatformView(), ), ], ), ); } Widget getMyPatformView() { if (defaultTargetPlatform == TargetPlatform.android) { return ...
// inside a setState call to trigger a rebuild. The framework then calls // build, below, which updates the visual appearance of the app. if (inCart) _shoppingCart.add(product); else _shoppingCart.remove(product); }); } @override Widget build(BuildContext context) { return new Scaffold...
@override Widgetbuild(BuildContext context){returnScaffold(// Page widget.appBar:AppBar(// Page app bar with title and back button if user can return to previous screen.title:Text(widget.title),// Text to display page title.),body:Center(// Widget to center child widget.child:Column(// ...
一个widget的构建函数应该是没有副作用的。每当函数被要求构建时,widget应该返回一个新的widgets树1,不管widget之前返回的是什么。框架会做繁重的工作,根据渲染对象树来决定哪些构建方法需要被调用(后面会详细介绍)。关于这个过程的更多信息可以在Inside Flutter主题中找到。
children:<Widget>[ _image==null? Text("未选择图片"): Image.file(_image), RaisedButton( child: Text("选择照片"), onPressed: _pickImage, ) ], ), ), ); }void_pickImage() async { File image=await ImagePicker.pickImage(source: ImageSource.gallery); ...
flutter: typically happens when a scrollable widget is nested inside another scrollable widget. flutter: If this widget is always nested in a scrollable widget there is no need to use a viewport because flutter: there will always be enough vertical space for the children. In this case, consider...
When you have an application, sometimes it's important to save widgets as images even if they're not on screen. An example of how this would be necessary: having a customized widget displayed in a thumbnail in the app but you wish to save as an image a full size/full screen version ...
Stand-alone widget tree with multiple render trees to enable multi-view rendering by @goderbauer in #125003 Skip the iteration in Layer._fireCompositionCallbacks if the callbacks map is empty by @jason-simmons in #130438 Guard access to dart:developer with !kReleaseMode by @goderbauer in #...
If true, and an appBar is specified, then the height of the body is extended to include the height of the app bar and the top of the body is aligned with the top of the app bar. final floatingActionButton → Widget? A button displayed floating above body, in the bottom right corner...