dictionary ContainsKey method

Question

Please explain why dictionary's 'getAt' method fails

List<BString> infoKeys = new List<BString>(infoDict.Keys); 
if (infoKeys.Contains(TorrentFileKeyWords.FILES_KEY) == true) //"files"
{   
        List<BaseType> multiFiles = ((BList)dict[TorrentFileKeyWords.FILES_KEY]).Value; <<< this fails

So infoDict is a Dictionary<String, BString> Contains on infoDict.Keys is used to find a specific item (of type BString) But line 4 fails... doesnt have sens

I am not used with c#.. so what methods do I have to override (now i have: GetHashCode, ==, != & equals)

You haven't presented enough code to help you properly, and you haven't presented the error either. Please read http://tinyurl.com/so-hints. — Jon Skeet, Apr 05 '12 at 19:54
What are the types really? If `infoDict` was a `Dictionary`, then `infoDict.Keys` would be a collection of `String`, not a collection of `BString`. — Guffa, Apr 05 '12 at 19:56

score 3 · Answer 1 · answered Apr 05 '12 at 19:56

You shouldn’t need to copy your Keys to a new list to perform the lookup. In fact, you can check whether the key is present in the dictionary and retrieve its associated value in a single operation using the TryGetValue method:

BList bList;
if (dict.TryGetValue(TorrentFileKeyWords.FILES_KEY, out bList))
{
    List<BaseType> multiFiles = bList.Value;
    // use multiFiles here
}

score 2 · Accepted Answer · answered Apr 05 '12 at 19:54

I suspect the problem is that you're using infoDict in one place, and dict in another...

It's not clear why you're creating a list from the keys of infoDict rather than just calling ContainsKey, or (better) using TryGetValue to start with. Additionally, I would advise against a "B" prefix for your type names.

dictionary ContainsKey method

2 Answers2