Question

I have been trying to check my arraylist to see if an object already exsists, but it always returns false. Does any one have a sugestion to what I am doing wrong with the arrayList.

ArrayList arr;

void Init()
{
   arr = new ArrayList();  

}

void Fred()
{   
   CauseAssignment ca = new CauseAssignment(Param1.Text, Param2.Text);
   if(!arr.Contains(ca))
       arr.Add(ca);

}



 public class CauseAssignment
{
    private string _Path;
    public string Path
    {
        get { return _Path; }
    }

    private string _DelimRootCause;
    public string DelimRootCause
    {
        get { return _DelimRootCause; }
    }

    public CauseAssignment(string path, string delimRootCause)
    {
        _Path = path;
        _DelimRootCause = delimRootCause;
    }
    public override string ToString()
    {
        return _Path;
    }
}

Answer 1

The Contains() methods of ArrayList determine equalitys using the implementation of Equals() available on the objects you store.

If you want two different instances of your class to be considered equivalent, you would need to override the Equals() method to return true when they are. You should also, then, overload GetHashCode() for consistency and usability in dictionaries. Here’s an example:

public class CauseAssignment
{
    private string _Path;

    /* the rest of your code */

    public override bool Equals( object o )
    { 
        if( o == null || o.GetType() != typeof(CauseAssignment) )
            return false;
        CauseAssignment ca = (CauseAssignment)o;
        return ca._Path.Equals( this._Path );
    }

    public override int GetHashCode()
    {
        return _Path.GetHashCode();
    }
}