Question

我有这个带有2个枚举字段的简单类，我试图在集合中找到该对象的一个项目（List<T>），但是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));
}

第一个断言正常

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

但第二个不是

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

Answer 1

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

以下是关于EqualityComparer<T>.Default如何运作的MSDN说明：

Default属性检查类型T是否实现了 System.IEquatable接口，如果是，则返回一个使用该实现的EqualityComparer。否则，它返回使用覆盖的EqualityComparer 由T。
提供Object.Equals和Object.GetHashCode

换句话说，您的Calculator课程应该实施System.IEquatable（不 System.IEqualityComparer！）界面或覆盖Object.Equals和Object.GetHashCode方法。

Answer 2

您没有在等号中使用IEqualityComparer<Calculator>并且包含两者。 EqualityComparer具有不同的意义。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。

IEqualityComparer和Contains方法

2 个答案: