a default value for a Dictionary in c#

Question

I have the following PageViewModel class:

public class PageViewModel : ViewModel<Page>
{
 public PageViewModel ()
        {
            Kywords = new List<Keyword>();
            AnswserKeywordDictionary = new Dictionary<string, Answer>();
        }
        public Company Company { get; set; }
        public List<Keyword> Kywords { get; set; }
        public Dictionary<string, Answer> AnswserKeywordDictionary { get; set; }
}

In my view i'm using the property AnswserKeywordDictionary like that:

@Html.DisplayAffirmativeAnswer(Model.AnswserKeywordDictionary["myKey"])

my question is : how can i return a default value if "myKey" is not in the dictionary.

Thanks in advance

i dont want ceck every time, i'm looking for something like when you use a get to return a value — Bilel Chaouadi, Sep 19 '14 at 13:36

score 5 · Accepted Answer · answered Sep 19 '14 at 13:29

Check if it exists, if not, return a default value:

Model.AnswserKeywordDictionary.ContainsKey("myKey")
    ? Model.AnswserKeywordDictionary["myKey"]
    : "default"

You could also create an extension method for that:

    public static Dictionary<K, V> GetValueOrDefault<K, V>(this Dictionary<K, V> dictionary, K key, V defaultValue)
    {
        V val;
        if (dictionary.TryGetValue(key, out val))
        {
            return val ?? defaultValue;
        }

        return defaultValue;
    }

Use it like this:

Model.AnswserKeywordDictionary.GetValueOrDefault("myKey", "default")

score 0 · Answer 2 · answered Sep 19 '14 at 13:31

0

Abstract your dictionary with a method:

public Dictionary<string, Answer> AnswserKeywordDictionary { get; set; }
public GetAnswer(string key, Answer defaultValue)
{
   if(AnswserKeywordDictionary.ContainsKey(key)
       return AnswserKeywordDictionary[key];
   return defaultValue;
}

then use that method in your View:

@Html.DisplayAffirmativeAnswer(Model.GetAnswer("myKey"))

answered Sep 19 '14 at 13:31

D Stanley

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thanks, for responding, but i don't use a call a method, i want something that return the default value automatically. like get in properties – Bilel Chaouadi Sep 19 '14 at 13:34
The add an extension method as suggested in the linked question. – D Stanley Sep 19 '14 at 13:39

a default value for a Dictionary in c#

2 Answers2