什么Collection.Contains（）用来检查现有的对象？ [英] What does Collection.Contains() use to check for existing objects?

问题描述

我有自定义对象的强类型列表中，MyObject的，其中有一个属性标识与其他属性一起。

比方说，一个为MyObject的ID定义它作为独特的，我想检查我的收藏还没有一个具有标识1之前，我想补充我的新MyObject来的集合MyObject的对象。

我想用，如果（！List.Contains（MyObj中）），但我怎么执行的事实，只有一MyObject来的两个属性把它定义为独特之处？

我可以使用IComparable的？或者，我只有重写的equals方法，但我需要先继承的东西是吗？

I have a strongly typed list of custom objects, MyObject, which has a property Id along with some other properties.
Let's say that the Id of a MyObject defines it as unique and I want to check if my collection doesn't already have a MyObject object that has an Id of 1 before I add my new MyObject to the collection.
I want to use if(!List.Contains(myObj)) but how do I enforce the fact that only one or two properties of MyObject define it as unique?
I can use IComparable? Or do I only have to override an Equals method but I'd need to inherit something first is that right?

感谢

推荐答案

列表< T>。载使用 EqualityComparer< T> .DEFAULT ，从而使用 IEquatable< T> 如果类型实现它，或者的Object.Equals ，否则

List<T>.Contains uses EqualityComparer<T>.Default, which in turn uses IEquatable<T> if the type implements it, or object.Equals otherwise.

您可以只实施 IEquatable< T> 但它是一个好主意，覆盖的Object.Equals 如果你这样做，和一个非常好主意覆盖的GetHashCode（）如果你这样做：

You could just implement IEquatable<T> but it's a good idea to override object.Equals if you do so, and a very good idea to override GetHashCode() if you do that:

public class SomeIDdClass : IEquatable<SomeIDdClass>
{
    private readonly int _id;
    public SomeIDdClass(int id)
    {
        _id = id;
    }
    public int Id
    {
        get { return _id; }
    }
    public bool Equals(SomeIDdClass other)
    {
        return null != other && _id == other._id;
    }
    public override bool Equals(object obj)
    {
        return Equals(obj as SomeIDdClass);
    }
    public override int GetHashCode()
    {
        return _id;
    }
}

请注意，该哈希代码涉及平等的准则。这是至关重要的。

Note that the hash code relates to the criteria for equality. This is vital.

这也使得它适用于任何其他情况下相等，通过具有相同的ID的定义，是有用的。如果你有一对的要求，检查列表有这样一个对象，那么我可能会建议只是在做：

This also makes it applicable for any other case where equality, as defined by having the same ID, is useful. If you have a one-of requirement to check if a list has such an object, then I'd probably suggest just doing:

return someList.Any(item => item.Id == cmpItem.Id);

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