Problem using List.Contains()

[Jeff]

..NET 2.0

I'm trying to use List.Contains to determine if an object already exist in
the list. This Contains method always return false in my code

In my code a method gets a list of names, the method will return a generic
list containing only the distinct names. This fails in my code

Example:
public class Car
[Serializable]
private string _name;
public Car(string name) { _name = name; }
}

List<Carcars = List<Car>();
Car car = new Car("Volvo");
list.Add(car);
car = new Car("Volvo");
if (!list.Contains(car))
List.Add(car) <<<<<<<<<<<< here is the problem in my code, Here
Contains didn't find the car("Volvo") already in the list, so this
if-statement fails and another car(volvo) object is added to the list

Maybe I instead should use Exists?

Any suggestions are welcome

[=?ISO-8859-1?Q?G=F6ran_Andersson?=]

Jeff wrote:

.NET 2.0

I'm trying to use List.Contains to determine if an object already exist in
the list. This Contains method always return false in my code

In my code a method gets a list of names, the method will return a generic
list containing only the distinct names. This fails in my code

Example:
public class Car
[Serializable]
private string _name;
public Car(string name) { _name = name; }
}

List<Carcars = List<Car>();
Car car = new Car("Volvo");
list.Add(car);
car = new Car("Volvo");
if (!list.Contains(car))
List.Add(car) <<<<<<<<<<<< here is the problem in my code, Here
Contains didn't find the car("Volvo") already in the list, so this
if-statement fails and another car(volvo) object is added to the list

Maybe I instead should use Exists?

Any suggestions are welcome

The Contains method checks if an item exists in the list. As this is a
list of references, it checks if the reference exists in the list.

The two Car objects that you create are separate objects, so they have
different references. The Contains method only looks for the reference,
so it doesn't find the existing object although it contains the same data.

Use a Dictionary<string, Car>, where the key is the name of the car.

--
Göran Andersson
_____
http://www.guffa.com

[Jon Skeet [C# MVP]]

On Aug 1, 1:19 pm, Göran Andersson <[e-mail]:

The Contains method checks if an item exists in the list. As this is
a list of references, it checks if the reference exists in the list.

No - it checks for items which are deemed to be equal. As Equals
hasn't been overridden, the default implementation is used, which is
just for reference equality. Your statement doesn't hold in general
though - a good example is a list of strings, where two separate
string objects with the same data are equal, and so List.Contains will
find one string given the other.

Jon