dart - 创建一部分 flutter 代码作为小部件和变量有什​​么区别

Question

我看到有些地方将代码块分配给小部件或变量，创建两者有什么区别？

示例代码如下:

  //creating new widget

  Widget ratingSection = Container(
  padding: const EdgeInsets.all(20.0),
  child: Row(
    mainAxisAlignment: MainAxisAlignment.spaceEvenly,
    children: [ ..............
    ],
  ),
);

//creating new var

 var ratingSectionVar = Container(
  padding: const EdgeInsets.all(20.0),
  child: Row(
    mainAxisAlignment: MainAxisAlignment.spaceEvenly,
    children: [ ..............
    ],
  ),
);

return MaterialApp( ......
     ....
    body: ListView(
      children: <Widget>[
        ratingSection,
        ratingSectionVar,
      ],
    ),
  ),
);

Answer 1

Dart 提供了一个叫做 Type inference 的东西

The analyzer can infer types for fields, methods, local variables, and most generic type arguments. When the analyzer doesn’t have enough information to infer a specific type, it uses the dynamic type.

因此，当您使用 var 关键字创建变量时，您可以从赋值语句的右侧获取类型所以 var ratingSectionVar = Container()意味着 ratingSectionVar 的 Type 是 Container 也是从 Widget 类派生的