objects in a c# arraylist

Question

I'm coming from a Javascript background which possibly is a good thing although so far it's proving to be a bad thing.

In Javascript, I have:

function doStuff(){
    var temp = new Array();
    temp.push(new marker("bday party"));
    alert(temp[0].whatsHappening); // 'bday party' would be alerted
}

function marker(whatsHappening) {
    this.whatsHappening = whatsHappening;
}

I would now like to do the same thing in C#. I have set up a class:

class marker
{
    public string whatsHappening;

    public marker(string w) {
        whatsHappening = w;
    }
}

and add a new object, but I can't seem to call the data in the same way:

ArrayList markers = new ArrayList();

markers.Add(new marker("asd"));
string temp = markers[0].whatsHappening; // This last bit isn't allowed

Darin Dimitrov · Accepted Answer · 2011-10-13 16:53:31Z

5

Use a generic List<T> instead:

List<marker> markers = new List<marker>();
markers.Add(new marker("asd"));
string temp = markers[0].whatsHappening;

answered Oct 13, 2011 at 16:53

Darin Dimitrov

1.0m277 gold badges3.3k silver badges3k bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Roland Mai · Accepted Answer · 2011-10-13 16:54:07Z

4

ArrayList is weakly typed. That means, all items in the array are objects. You need to cast them to your class:

string temp = ((marker)markers[0]).whatsHappening;

You should use a List<marker> instead.

answered Oct 13, 2011 at 16:54

Roland Mai

31.2k8 gold badges58 silver badges61 bronze badges

Comments

Anthony Pegram · Accepted Answer · 2011-10-13 17:01:56Z

To use it from an ArrayList, you must first cast it to the appropriate type. ArrayList stores items as object.

var item = (marker)markers[0];
// item.Foo is now accessible

However, assuming you're using a version of C# released since 2005 (ie., C# 2.0+), you will be better off using List<T>, where T is the type of the object. It's strongly typed, can only store items of type T, and does not require casts to perform operations.

List<marker> markers = new List<marker>();
markers.Add(new marker()); // legal
markers.Add(1); // not legal, but would be allowed with ArrayList

List<T> is available in the System.Collections.Generic namespace.

Unrelated, since you're new to C#, learn the conventions of the language that virtually all C# developers adhere to. A few basic ones: class names, properties, methods are PascalCased, private members, parameters, local variables are camelCased, and class data is exposed as properties, not as publicly accessible fields.

public class Marker
{
    public string WhatsHappening { get; set; } // exposed as property 

    string foo; // member field, is implicitly private

    public void DoFrobbing(Bar thingToFrob)
    {
        int localVariable;
    }
}

ordag · Accepted Answer · 2011-10-13 16:53:22Z

1

ArrayList holds a list of Objects. Try to use the generic System.Collections.Generic.List<T>:

List<marker> markers = new List<marker>();

answered Oct 13, 2011 at 16:53

ordag

2,5475 gold badges26 silver badges35 bronze badges

Collectives™ on Stack Overflow

objects in a c# arraylist

4 Answers 4

Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related