Question

我有一个班级：

private class Part
{
    public string Id { get; set; }
    public string Class { get; set; }

    public override bool Equals(object obj)
    {
        Part part = obj as Part;

        return this.Id == part.Id;
    }
}

此外，我有一个这个类的列表，所以我需要在此列表中使用distinct。多数民众赞成在做什么：

List<Part> parts = new List<Part>();
//adding items
parts = parts.Distinct().ToList();

但没有任何反应。谁能告诉我什么错了？

Answer 1

覆盖Equals时，您还必须覆盖GetHashCode：

private class Part
{
    public string Id { get; set; }
    public string Class { get; set; }

    // Whenever overiding Equals
    // You have to override this method too
    public override int GetHashCode() {
      return String.IsNullOrEmpty(Id) ? 0 : Id.GetHashCode();
    }

    public override bool Equals(object obj)
    {
        Part part = obj as Part;

        // if obj is not of Part you should return false
        if (Object.ReferenceEquals(null, part))
          return false; 

        return this.Id == part.Id;
    }
}

错误行为的原因是Distinct 首次测试 GetHashCode和只有 Equals。

Answer 2

要对您的班级执行Distinct操作，您需要提供IEqualityComparer<T>

的Comparer实施

示例：

public class SelectedItemComparer : IEqualityComparer<Part> { public new bool Equals(Part x, Part y) { return x.Id == y.Id; } public int GetHashCode(Part source) { string code = source.Id.ToString(); return code.GetHashCode(); } }

<强>用法：

List<Part> parts = new List<Part>(); //adding items parts = parts.Distinct(new SelectedItemComparer()).ToList();

参考：Distinctly LINQ – Getting a Distinct List of Objects

与我班级的名单不同

2 个答案: