Question

I use dictionary in my program like this

Dictionary<string, List<Term>>

which Term is object from class has two fields (name , id)
I need add new object into dictionary where the name of new object is not found in the dictionary…
if the field name in new object is existent as name of old object I will not add it..
can you help me
the code I use is

 foreach (string term in terms)
    {
        if (!dictionary.ContainsKey(term))
        {
            dictionary.Add(term, new List<Term>());
        }

        Term TT=new Term(i,name);
        if (!dictionary[term].Contains(TT))
        {
            dictionary[term].Add(TT);


        }

this code dosn’t work exactly..

Answer 1

The problem is here:

    if (!dictionary[term].Contains(TT))
    {
        dictionary[term].Add(TT);
    }

The default behavior of List.Contains if class Term does not implement IEquatable<Term> is to check for reference equality. Since the object you just constructed cannot already be in the list, Contains will always return false and the new Term will always be added.

One good solution would be to implement IEquatable<Term> in Term and specify the criteria you want for equality in the IEquatable<Term>.Equals method.

Another solution (which is probably less desirable because it will only help this particular piece of code to work) is to change the test to

    // Change the t.name == TT.name test to whatever your idea
    // of "term X equals term Y" is
    if (dictionary[term].FindIndex(t => t.name == TT.name) == -1)
    {
        dictionary[term].Add(TT);
    }