How to write a class that (like array) can be indexed with `arr[key]`?

问题

Like we do Session.Add("LoginUserId", 123); and then we can access Session["LoginUserId"], like an Array, how do we implement it?

回答1:

You need an indexer:

public Thing this[string index]
{
    get
    {
         // get the item for that index.
         return YourGetItemMethod(index)
    }
    set
    {
        // set the item for this index. value will be of type Thing.
        YourAddItemMethod(index, value)
    }
}

This will let you use your class objects like an array:

MyClass cl = new MyClass();
cl["hello"] = anotherObject;
// etc.

There's also a tutorial available if you need more help.

Addendum:

You mention that you wanted this to be available on a static class. That get's a little more complicated, because you can't use a static indexer. If you want to use an indexer, you'd need to access it off of a static Field or some such sorcery as in this answer.

回答2:

You should use indexers See the link: http://msdn.microsoft.com/en-us/library/2549tw02.aspx

回答3:

Sounds like all you need is a generic dictionary.

var session = new Dictionary<string, object>();

//set value
session.Add("key", value);

//get value
var value = session["key"] as string;

If you want to make this static, just make it a static member in another class.

public static class SharedStorage
{
   private static Dictionary<string, object> _data = new Dictionary<string,object>();
   public static Dictionary<string, object> Data { get { return _data; } }
}

Then you can access it as such, without having to initialize it:

SharedStorage.Data.Add("someKey", "someValue");
string someValue = (string) SharedStorage.Data["someKey"];

If you want to be more adventurous and are using .NET 4 you can also use an Expando Object, like the ViewBag member available to controllers in ASP.NET MVC 3:

dynamic expando = new ExpandoObject();
expando.UserId = 5;
var userId = (int) expando.UserId;

回答4:

With the way you usually use the Session variable all you really need is a generic Dictionary collection like this one. You don't really need to write a class. But if you need to add extra functionality and/or semantics you could certainly wrap the collection with a class and just include and indexer.

For other collections check out the Collections.Generic namespace.

来源：https://stackoverflow.com/questions/6807310/how-to-write-a-class-that-like-array-can-be-indexed-with-arrkey

标签

.net

arrays

indexer