* dart 控制语句(if/else, switch/case, while/do-while, for) */import'package:flutter/material.dart';import'package:flutter_demo/helper.dart';classDartStatementextendsStatelessWidget{constDartStatement({Key? key}) :super(key: key);@overrideWidget build(BuildContext context) {// if/elsesample1()...
在编写应用程序时,通常会创建新的widget,这些widget是无状态的StatelessWidget或者是有状态的StatefulWidget, 具体的选择取决于您的widget是否需要管理一些状态。widget的主要工作是实现一个build函数,用以构建自身。一个widget通常由一些较低级别widget组成。Flutter框架将依次构建这些widget,直到构建到最底层的子widget时,这些...
toggle; }); } _getToggleChild() { if (toggle) { return Text('Toggle One'); } else { return MaterialButton(onPressed: () {}, child: Text('Toggle Two')); } } @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar( title: Text("Sample App"), ), body:...
条件语句中的else 什么是else else 就是对于if条件不满足的时候执行另一个代码块的入口 功能当if语句不满足时所执行的代码块的入口用法 if bool_result : do else...: elsedo # else语法快 , 需缩进 # 缩进等级与do语法块一致 参数 elsed...
已经存在一个model对象, model内部数据发生变化时会以回调的形式给外部通知;现在需要根据model自己不同的判断条件创建不同的widget对象;build方法类似如下代码: @overrideWidget build(BuildContext context) {if(model.condition1) {returnWidget1(); }elseif(model.condition2) {returnWidget2(); ...
控件类型从StatelessWidget到StatefulWidget的转换,因为Flutter在执行热刷新时会保留程序原来的state,而某个控件从stageless→stateful后会导致Flutter重新创建控件时报错“myWidget is not a subtype of StatelessWidget”,而从stateful→stateless会报错“type ‘myWidget’ is not a subtype of type ‘StatefulWidget’ of ...
=null){if(oldChild.widget.key!=null){oldKeyedChildren[oldChild.widget.key!]=oldChild;}else{...
which causes it to rerun// the build method below so that the display can reflect the// updated values. If we changed _counter without calling// setState(), then the build method would not be called again,// and so nothing would appear to happen._counter++;});}@overrideWidgetbuild(Bui...
Map<String,int> _outputMap = <String,int>{};void_output(Widget widget) {finalStringtypeName = widget.runtimeType.toString();if(_outputMap.containsKey(typeName)) { _outputMap[typeName] = _outputMap[typeName] +1; }else{ _outputMap[typeName] =1; ...
if (incomingWidgets != null) _inheritedWidgets = HashMap<Type, InheritedElement>.from(incomingWidgets); else _inheritedWidgets = HashMap<Type, InheritedElement>(); _inheritedWidgets[widget.runtimeType] = this; } @override void debugDeactivated() { ...