C#-Indexed Properties?

Question

I\'ve been using Visual Basic for quite a while and have recently made the decision to begin learning C# as a step forward into learning more complex languages.

As a

Answer 1

Indexers allow instances of a class or struct to be indexed just like arrays. Indexers resemble properties except that their accessors take parameters.

http://msdn.microsoft.com/en-us/library/6x16t2tx.aspx

Indexers are defined using the this keyword like this:

public T this[int i]
{
    get
    {
        // This indexer is very simple, and just returns or sets
        // the corresponding element from the internal array.
        return arr[i];
    }
    set
    {
        arr[i] = value;
    }
}

The .NET class library design guidelines recommend having only one indexer per class.

You can overload indexers based on the indexing parameter type

public int this[int i]
public string this[string s]

but not based on the return value

// NOT valid
public int this[int i]
public string this[int i]

Answer 2

I don't think you can specify a property only accessible with indexing, but you could just return an indexable value (like an array or List) and use [] on the result:

public List<Aclass> Aproperty
{
    get 
    {
         return this.theList;
    }
}

Aclass foo = this.Apropety[0];

Of course, anything with an indexer will work instead of List.

Or, you could do it the other way around: define an indexer (on the class itself) that returns an object that has a property Aproperty, used like so: Aclass foo = this[0].Aproperty.

Answer 3

Since C# doesn't support parameterized properties (which is what you are showing), you need to convert this code to two functions, a GetAProperty(index) and a SetAProperty(index).

We converted a 50,000+ LOC application from VB to C# and it required extensive modifications like this due to the dependence on parameterized properties. However, it is doable, it just requires a different way of thinking about properties like this.