Question

I have a class like this:

public class SomeClass
{
    private const string sessionKey = "__Privileges";
    public Dictionary<int, Privilege> Privileges
    {
        get
        {
            if (Session[sessionKey] == null)
            {
                Session[sessionKey] = new Dictionary<int, Privilege>();
            }

            return (Dictionary<int, Privilege>)Session[sessionKey];
        }
    }
}

Now, if Ido this…

var someClass = new SomeClass();
var p = someClass.Privileges[13];

… and there is no key 13, I will get an error like this:

The given key was not present in the dictionary.

I would like to have a property that can be accessed in the same way as above, but will return a default object in case of the absence of the key.

I tried creating an indexer property like this…

    public Privilege Privileges[int key]
    {
        get
        {
            try { return _privileges[key]; }
            catch { return new Privilege(); }
        }
    }

… but it looks like that’s not a C# 2008 language feature.

How can I access the property in the same way, but get the default object if the key isn’t present?

Answer 1

You’ll have to define your own IDictionary-based class with an indexer that has the desired behavior, and return an instance of that, rather than the stock Dictionary class, in your property getter.