Flutter Map的基本使用

我们先点进Map中查看代码：

可以看到这里需要两个值分别是 K和V

关于Map对象，通过{}初始化Map对象，每个元素形式为Key:Value

键(Key)和值(Value)之间使用冒号" : "分割

元素之间使用分号";"分割

基本使用方式:

Map student = {1: "Tm1", 2: "Jr1", 3: "spk1"};  print(student); //{1: Tm, 2: Jr, 3: spk}

  先创建Map 对象在进行赋值

Map president = {};  president[1] = "Tm2";  president[2] = "Jr2";  president[3] = "spk2";  print(president); //{1: Tm2, 2: Jr2, 3: spk2}

常见属性:

  Map map1 = Map();  map1["map1"] = 1;  map1["map2"] = 2;  map1["map3"] = 3;  print(map1.length); //长度  print(map1.isEmpty); //是否为空  print(map1.isNotEmpty); //是否不为空

常见方法:

 //常见使用方法  //新增一个键值对  Map map2 = Map();  map2["map1"] = 1;  print(map2); //{a8: 1}  //改变一个键值对  map2['a8'] = 2;  print(map2); //{a8: 2}

map还可以这样使用:

class _MyApp1State extends State {  @override  Widget build(BuildContext context) {    return Scaffold(        body: Column(            children: [      Container(        color: Colors.blue,        width: 100,        height: 100,      ),      Container(        color: Colors.green,        width: 100,        height: 100,      ),      Container(        color: Colors.red,        width: 100,        height: 100,      )    ].map((Widget widget) {      return SizedBox(        child: widget,      );    }).toList()));  }}

这时候我们就可以一起管理了，减少多余代码，更加优雅简洁

有时候我们需要分别管理，例如1，2需要改变,  3,4又有其他改变，这时候我们可以这样做

class MyApp1 extends StatefulWidget {  const MyApp1({Key? key}) : super(key: key);  @override  _MyApp1State createState() => _MyApp1State();}class _MyApp1State extends State {  @override  Widget build(BuildContext context) {    return Scaffold(      body: Column(          children: [        Container(          key: ValueKey('1'),          width: 500,          height: 500,          color: Colors.green.withOpacity(.2),        ),        Container(          key: ValueKey('2'),          width: 500,          height: 500,          color: Colors.red.withOpacity(.2),        ),        Container(          key: ValueKey('3'),          width: 500,          height: 500,          color: Colors.blue.withOpacity(.2),        ),      ].map((Widget widget) {        double w = 100;        double h = 100;        if (widget.key == Key('1')) {          w = 50;          h = 50;        } else if (widget.key == Key('2')) {          w = 100;          h = 100;        } else if (widget.key == Key('3')) {          w = 150;          h = 150;        }        return SizedBox(          width: w,          height: h,          child: widget,        );      }).toList()),    );  }}

来源地址：https://blog.csdn.net/a3244005396/article/details/127669603