Dart流- skipWhile不跳过事件

Question

似乎skipWhile什么都没做..。还是我理解错了？

下面的代码..。我期待skipWhile删除两个条目！

Dart版本(来自颤振医生)：Dart version 2.9.0 (build 2.9.0-10.0.dev 7706afbcf5)

import 'package:flutter_test/flutter_test.dart';

class Car {
  final String name;
  final bool active;
  final int wheels;

  Car({this.name, this.active=true, this.wheels=4});
}

void main() {
  test("Check skipWhile", () {
    List dataSet = [
      Car(name: "Thunder", active: false),
      Car(name: "Lightening", active: false),
      Car(name: "Dinky", wheels: 3),
      Car(name: "Camry"),
      Car(name: "Outback"),
    ];

    List activeCars = dataSet.skipWhile((car) => car.active).toList();

    expect(activeCars.length, 3);
  });
}

Answer 1

如果您阅读了skipWhile的文档，您将看到：

返回一个Iterable，它在满足测试时跳过前导元素。

所以它只是跳过了主导元素，而不是所有元素。

相反，您需要的是where，它可以：

返回一个新的惰性Iterable，它包含满足谓词测试的所有元素。

因此，如果我在示例中将您的skipWhile更改为where，那么现在我将得到3的长度：

class Car {
  final String name;
  final bool active;
  final int wheels;

  Car({this.name, this.active = true, this.wheels = 4});
}

void main() {
  final dataSet = [
    Car(name: "Thunder", active: false),
    Car(name: "Lightening", active: false),
    Car(name: "Dinky", wheels: 3),
    Car(name: "Camry"),
    Car(name: "Outback"),
  ];

  final activeCars = dataSet.where((car) => car.active).toList();

  print(activeCars.length); // 3
}