确定两个对象是否相等

Question

I'm trying to test whether an object is equal to one in a list of objects given certain criteria (is name equal) and if it is, don't add it to list, otherwise add it. I have to use a method with this signature "static int Find(List c, Coffee x)". Find seeks x in c and returns a valid index (ie, 0, 1, …) if x exists in c, returns -1 otherwise. My equals method doesn't seem to realize the names are the same when I pass exact matches. Why is this? Here's my code:

        Coffee obv = new Coffee();
        Decaf decafCoffee = null;
        Regular regularCoffee = null;
        List<Coffee> inventory = new List<Coffee>();

        if (some sxpression)
            {
                decafCoffee = new Decaf(name, D, C, M);
                find = obv.Find(inventory, decafCoffee);
                if (find == -1)
                {
                    inventory.Add(decafCoffee);
                }
            }


          public class Coffee : IDisposable
          {
              public override bool Equals(object obj)
              {
                  if (obj is Coffee)
                  {
                    bool isNameEqual = Name.Equals(this.Name);

                 return (isNameEqual);
                  }
        return false;
    }

        public int Find(List<Coffee> c, Coffee x)
    {
        if (c.Equals(x))
        {
            return 0;
        }

        return -1;
    }
        }          

Answer 1

You are testing for equality on the List to an instance of Coffee. This will always return -1. What you want is c.Contains(x). Keep in mind when you override Equals you should also provide a similar override for GetHashCode(). Look here for Microsoft advice on implementing and overriding Equals on an object.

public int Find(List<Coffee> c, Coffee x) {
    return c.IndexOf(x);
}

public override int GetHashCode()
{
    return Name == null ? 0 : Name.GetHashCode();
}

Answer 2

Your error is here:

public int Find(List<Coffee> c, Coffee x)
{
    if (c.Equals(x))  // <-- this will never return true
    {
        return 0;
    }

    return -1;
}

However, your Find method is unnecessary. Use List<T>.IndexOf to keep your concept:

var index = inventory.IndexOf(decafCoffee);

Answer 3

Your problem is here:

public int Find(List<Coffee> c, Coffee x)
{
    if (c.Equals(x))
    {
        return 0;
    }

    return -1;
}

c is a List<Coffee> not a Coffee object.

You need to change your code so that it iterates over the list to see if it contains x :

for (int i = 0; i < c.Count; ++i)
    if (c[i].Equals(x))
        return i;

return -1

Answer 4

You can do as below, since you have Equals method you can use it for finding matching item

public int Find(List<Coffee> c, Coffee x)
{
    if (c.Any(i=>i.Equals(x))
    {
        return 0;
    }

    return -1;
}