IEqualityComparer 和 Contains 方法

Question

我有一个包含这 2 个枚举字段的简单类，我试图在集合中找到该对象的一项 (List<T>)，但 Contains 方法无法正常工作

public class Calculator : IEqualityComparer<Calculator>
{
    public DashboardsComputationMode ComputationMode { get; set; }
    public Modes Mode { get; set; }

    public Calculator(DashboardsComputationMode dashboardsComputationMode, Modes mode)
    {
        ComputationMode = dashboardsComputationMode;
        Mode = mode;
    }

    public bool Equals(Calculator x, Calculator y)
    {
        return (x.ComputationMode.Equals(y.ComputationMode) && x.Mode.Equals(y.Mode));
    }

    public int GetHashCode(Calculator obj)
    {
        return obj.ComputationMode.GetHashCode() ^ obj.Mode.GetHashCode();
    }
}

public enum DashboardsComputationMode
{
    Weighted = 0,
    Aggregated = 1,
    PR = 2,
    CurrentValue = 3,
    EquivalentHours = 4,
    AggregatedCorrected = 5,
    PRCorrected = 6
}

public enum Modes
{
    InstantaneousMode = 0,
    DailyMode = 1,
    MonthlyMode = 2,
    YearlyMode = 5,
    Undefined = 4,
}

为什么这个测试不起作用

[TestMethod]
public void TestMethod1()
{
  var list = new List<Calculator>()
  {
    new Calculator(DashboardsComputationMode.PR, Modes.DailyMode),
    new Calculator(DashboardsComputationMode.CurrentValue, Modes.YearlyMode),
    new Calculator(DashboardsComputationMode.PRCorrected, Modes.MonthlyMode)
  };

  var item = new Calculator(DashboardsComputationMode.CurrentValue, Modes.YearlyMode);
  Assert.IsTrue(list[1].Equals(item));
  Assert.IsTrue(list.Contains(item));
}

第一个断言工作正常

Assert.IsTrue(list[1].Equals(item)) 

但第二个没有

Assert.IsTrue(list.Contains(item));

Answer 1

List<T>.Contains 使用默认的相等比较器（EqualityComparer<T>.Default 返回的比较器）确定相等。

这是关于 EqualityComparer<T>.Default 工作原理的 MSDN 说明：

Default 属性检查类型 T 是否实现 System.IEquatable 接口，如果是，则返回一个 EqualityComparer 使用该实现。否则，它 返回一个EqualityComparer，它使用 Object.Equals和Object.GetHashCode由T提供。

换句话说，您的Calculator 类应该实现System.IEquatable（不是System.IEqualityComparer！）接口或覆盖Object.Equals 和Object.GetHashCode 方法。

Answer 2

您没有在 Equals 和 Contains 中使用 IEqualityComparer<Calculator>。 EqualityComparer 有不同的意义。我为你更正了代码。

  public class CalculatorComparer : IEqualityComparer<Calculator>
{

    public bool Equals(Calculator x, Calculator y)
    {
        return (x.ComputationMode.Equals(y.ComputationMode) && x.Mode.Equals(y.Mode));
    }

    public int GetHashCode(Calculator obj)
    {
        return obj.ComputationMode.GetHashCode() ^ obj.Mode.GetHashCode();
    }
}
public class Calculator
{
    public DashboardsComputationMode ComputationMode { get; set; }
    public Modes Mode { get; set; }

    public Calculator(DashboardsComputationMode dashboardsComputationMode, Modes mode)
    {
        ComputationMode = dashboardsComputationMode;
        Mode = mode;
    }


    public override bool Equals(object obj)
    {
        Calculator y = obj as Calculator;

        return (this.ComputationMode.Equals(y.ComputationMode) && this.Mode.Equals(y.Mode));
    }
}

public enum DashboardsComputationMode
{
    Weighted = 0,
    Aggregated = 1,
    PR = 2,
    CurrentValue = 3,
    EquivalentHours = 4,
    AggregatedCorrected = 5,
    PRCorrected = 6
}

public enum Modes
{
    InstantaneousMode = 0,
    DailyMode = 1,
    MonthlyMode = 2,
    YearlyMode = 5,
    Undefined = 4,
}

现在两者都应该返回 true。