使用 IEqualityComparer 基于 C# 中的两个属性生成不同的列表

Question

我正在尝试生成一个由两个字符串串联而成的项目列表框。我创建了一个实现 IEqualityComparer 的 class，我想让这个列表与众不同。

private void PopulateFamily()
    {
        var source = _mfgOrdersData
            .Select(o => new FamilySelector(o.ItemWrapper.ItemClass, o.ItemWrapper.Family))
            .Distinct()
            .OrderBy(f => f.CodeFamily)
            .ToList();

        FamilyFilterListBox.DataSource = source;
        FamilyFilterListBox.ValueMember = "Family";
        FamilyFilterListBox.DisplayMember = "CodeFamily";
    }

class FamilySelector : IEqualityComparer<FamilySelector>
{
    public FamilySelector(string code, string family)
    {
        Code = code;
        Family = family;
    }

    public string Code { get; set; }
    public string Family { get; set; }
    public string CodeFamily { get { return string.Format("{0}\t{1}", Code, Family); } }

    public bool Equals(FamilySelector x, FamilySelector y)
    {
        return x.Code == y.Code && x.Family == y.Family;
    }

    public int GetHashCode(FamilySelector obj)
    {
        return obj.Code.GetHashCode() ^ obj.Family.GetHashCode();
    }
}

问题是我得到的列表不明确。同一项目出现多次。我认为 Equals() 或 GetHashCode() 没有正确实现。

Answer 1

目前您运行 Distinct() 在 FamilySelector 个实例的集合上，这导致通过引用相等进行比较。

要正确执行，您应该将 IEqualityComparer 的实例传递给 Distinct() 调用：

var source = _mfgOrdersData
    .Select(o => new FamilySelector(o.ItemWrapper.ItemClass, o.ItemWrapper.Family))
    .Distinct(new FamilySelector())
    .OrderBy(f => f.CodeFamily)
    .ToList();

您应该将无参数构造函数添加到 FamilySelector class 以便可以编译代码。

我还建议对 FamilySelector class 进行小规模重构。目前它保存数据并进行比较。通常 IEqualityComparer 的实现是 data-less class ，它只执行比较：

class FamilyData
{
    public FamilyData(string code, string family)
    {
        Code = code;
        Family = family;
    }

    public string Code { get; set; }
    public string Family { get; set; }
    public string CodeFamily { get { return string.Format("{0}\t{1}", Code, Family); } }
}

class FamilySelector : IEqualityComparer<FamilyData>
{
    public bool Equals(FamilyData x, FamilyData y)
    {
        return x.Code == y.Code && x.Family == y.Family;
    }

    public int GetHashCode(FamilyData obj)
    {
        return obj.Code.GetHashCode() ^ obj.Family.GetHashCode();
    }
}

var source = _mfgOrdersData
    .Select(o => new FamilyData(o.ItemWrapper.ItemClass, o.ItemWrapper.Family))
    .Distinct(new FamilySelector())
    .OrderBy(f => f.CodeFamily)
    .ToList();

Answer 2

CodeFuller 的答案可以正常工作，但作为替代选项，您可以使用 MoreLINQ 及其 DistinctBy 方法，这将避免您需要创建一个单独的 class :

private void PopulateFamily()
{
    var source = _mfgOrdersData
        .Select(o => o.ItemWrapper)
        .DistinctBy(o => new { o.ItemClass, o.Family })
        .OrderBy(f => f.CodeFamily)
        .ToList();

    FamilyFilterListBox.DataSource = source;
    FamilyFilterListBox.ValueMember = "Family";
    FamilyFilterListBox.DisplayMember = "CodeFamily";
}

我假设您想要 select ItemWrapper - 如果不查看所涉及的类型很难判断，但这看起来可能就是您想要的。

使用 IEqualityComparer 基于 C# 中的两个属性生成不同的列表

Use IEqualityComparer to generate a distinct list based on two properties in C#

c#

linq

iequalitycomparer