c# List.Contains() Method Returns False

Question

In the code block below I would expect dictCars to contain: { Chevy:Camaro, Dodge:Charger }

But, dictCars comes back empty. Because this line returns false each time it

Answer 1

You need to implement the IEqualityComparer

More information on how to do it can be found here; http://msdn.microsoft.com/en-us/library/bb339118.aspx

// Custom comparer for the class 
 class CarComparer : IEqualityComparer
{
// Products are equal if their names and product numbers are equal. 
public bool Equals(Car x, Car y)
{

    //Check whether the compared objects reference the same data. 
    if (Object.ReferenceEquals(x, y)) return true;

    //Check whether any of the compared objects is null. 
    if (Object.ReferenceEquals(x, null) || Object.ReferenceEquals(y, null))
        return false;

    //Check whether the properties are equal. 
    return x.CarID == y.CarID && x.CarName == y.CarName;
}

// If Equals() returns true for a pair of objects  
// then GetHashCode() must return the same value for these objects. 

public int GetHashCode(Car car)
{
    //Check whether the object is null 
    if (Object.ReferenceEquals(car, null)) return 0;

    //Get hash code for the Name field if it is not null. 
    string hashCarName = car.CarName == null ? 0 : car.CarName.GetHashCode();

    //Get hash code for the ID field. 
    int hashCarID = car.CarID.GetHashCode();

    //Calculate the hash code for the product. 
    return hashCarName ^ hashCarID;
}

Check for equality;

CarComparer carComp = new CarComparer();
bool blnIsEqual = CarList1.Contains(CarList2, carComp);