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I have a custom collection as shown below

public class CustomCollection<T>:IEnumerable<T>, IEnumerator<T>
{
    int size = 0;
    int current = 0;
    int position = -1;
    CustomComparer<T> cmp = new CustomComparer<T>();

    T[] collection = null;
    public CustomCollection(int sizeofColl)
    {
        size = sizeofColl;
        collection = new T[size];
    }

    public void Push(T value)
    {
        if (!collection.Contains(value, cmp))
            collection[current++] = value;
    }

    public T Pop()
    {
        return collection[--current];
    }        

    IEnumerator<T> IEnumerable<T>.GetEnumerator()
    {
        return (IEnumerator<T>)this;
    }

    System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
    {
        throw new NotImplementedException();
    }

    public T Current
    {
        get { return collection[position]; }
    }

    public void Dispose()
    {

    }

    object System.Collections.IEnumerator.Current
    {
        get { throw new NotImplementedException(); }
    }

    public bool MoveNext()
    {
        position++;
        if (position >= collection.Length)
            return false;
        else
            return true;
    }

    public void Reset()
    {
        throw new NotImplementedException();
    }
}

Now I want to have a collection of Person class which is as below along with the IEqualityComparer

 public class Person
{
    public string Name { get; set; }
    public int ID { get; set; }       
}

public class CustomComparer<T>:IEqualityComparer<T>    {


    public bool Equals(T x, T y)
    {
        Person p1 = x as Person;
        Person p2 = y as Person;
        if (p1 == null || p2 == null)
            return false;
        else
            return p1.Name.Equals(p2.Name);
    }

    public int GetHashCode(T obj)
    {
        Person p = obj as Person;
        return p.Name.GetHashCode();
    }
}

Now when I perform the following operation on the collection, why only Equals Method is called and not the GetHashCode() ?

  CustomCollection.CustomCollection<Person> custColl = new CustomCollection<Person>(3);
        custColl.Push(new Person() { Name = "per1", ID = 1 });
        custColl.Push(new Person() { Name = "per2", ID = 2 });
        custColl.Push(new Person() { Name = "per1", ID = 1 });

Or how can I make my code to call GetHashCode ?

4

1 回答 1

2

这与以下行有关：

if (!collection.Contains(value, cmp))

对向量或序列的测试（因为它看起来像）在调用;Enumerable.Contains时没有任何目的。GetHashCode()如果数据已被分组到散列桶或其他优化结构中，这很有用，但这里的数据只是一个平面的值序列。如果它需要调用一个方法，它最好调用Equals而不是GetHashCode()，因为如果哈希相同，它仍然需要调用Equals（哈希码表示不相等，但不能表示相等）。因此，可以选择每个对象只调用一个方法，而不是每个对象至少一个方法，每个对象可能有两个方法。第一个显然更可取。

如果数据是 aDictionary<Person, ...>或 a HashSet<Person>，那么我希望GetHashCode()被使用。

于 2013-03-07T10:09:29.903 回答