声明什么类型

Question

所以有这样一个类

class Base<T extends BaseClass> extends StatefulWidget

并且我想使用该类而不直接提供扩展 BaseClass 的对象，而是通过构造函数传递一些东西。

class Something extends StatelessWidget {
  final /*what type I am supposed to give here*/ test;

  const Something({Key key, this.test}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Base<test>();
  }
}

我得到的错误警告是

'dynamic' doesn't extend 'BaseClass'.
Try using a type that is or is a subclass of 'BaseClass'.dart(type_argument_not_matching_bounds)

The name 'test' isn't a type so it can't be used as a type argument.
Try correcting the name to an existing type, or defining a type named 'test'.dart(non_type_as_type_argument)

Answer 1

您可以通过“类型”声明，但不能从表示类的 Type 对象创建类的实例。

class Something<T extends BaseClass> extends StatelessWidget {
  // final Type test;

  // const Something({Key key, this.test}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Base<T>();
  }
}

创建一些小部件：

class NewClass extends BaseClass {}

Widget x = Something<NewClass>();