flutter中dart语言之‘$‘的使用

字符串可以通过 ${expression} 的方式内嵌表达式。 如果表达式是一个标识符&＃xff0c;则 {} 可以省略。
在 Dart 中通过调用就对象的 toString() 方法来得到对象相应的字符串。

var s &＃61; &＃39;string interpolation&＃39;;assert(&＃39;Dart has $s, which is very handy.&＃39; &＃61;&＃61;&＃39;Dart has string interpolation, &＃39; &＃43;&＃39;which is very handy.&＃39;);
assert(&＃39;That deserves all caps. &＃39; &＃43;&＃39;${s.toUpperCase()} is very handy!&＃39; &＃61;&＃61;&＃39;That deserves all caps. &＃39; &＃43;&＃39;STRING INTERPOLATION is very handy!&＃39;);


但是如果s是一个类的实例成员变量&＃xff0c;则不能省略{}&＃xff0c;否则在$引用该变量时会出现问题&＃xff0c;如&＃xff1a;

var user &＃61; User(); //这里实例化一个类Widget _UserInfotmation(){return Container(child: Row(children: [Column(children: [FlatButton(onPressed: (){print(user.id); //点击输入000001&＃xff0c;正确&＃xff0c;user.id是一个类成员print(user.name);},child: Image(image: AssetImage(user.headImage),width: 150.0,height: 150.0,))],),Column(children: [Text(&＃39;Name: $user.name&＃39; //此处不加花括号&＃xff0c;则会显示Instance of User.name&＃xff0c;正确的显示应该是000001),Text(&＃39;ID: $user.id&＃39;),],)],),);}