dart - Dart流-跳过但不跳过事件

Question

似乎不像skipWhile正在执行任何操作...还是我理解这个错误？

下面的代码...我期望skipWhile删除两个条目!

Dart版本(来自Flutter Doctor):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 skipWhile 的文档，则会看到:

Returns an Iterable that skips leading elements while test is satisfied.

因此，它只是跳过了主要元素，而不是所有元素。

您正确想要的是 where ，它可以:

Returns a new lazy Iterable with all elements that satisfy the predicate test.

因此，如果在您的示例中将 skipWhile更改为 where，则现在的长度为3:

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
}