CompareTo() With Generic List of Classes

19y2.6kVisual Basic .NET

I have a class that is built like this:

private class Site
{
    private string name;
    private string uniqueID;

    internal string Name
    {
       get { return this.name; }
       set { this.name = value; }
    }
    internal string UniqueID
    {
       get { return this.uniqueID; }
       set { this.uniqueID = value; }
    }

    public int CompareTo(object site)
    {
       return String.Compare(this.uniqueID, ((Site)site).uniqueID);
    }
}

And in another class, I have a generic list of these Site classes.

public sealed class SiteList
{
    private List<Site> pendingSiteList = new List<Site>;

    public bool IDExists(string uniqueID)
    {
       //This is where the problem lays
       int index = pendingSiteList.BinarySearch();

       if(index >= 0)
          return true;
       else
          return false;
    }

    public List<Site> PendingSiteList
    {
       get { return this.pendingSiteList; }
    }
}

I supposed the main problem is that I want to search the generic site lists to find out if a specified unique ID exists in any of the contained sites. But therin lay a problem in that the binary search method of a the generic list is expecting data of the type "Site" (strongly typed I suppose...), not string. I need to search this list by unique ID if thats possible. Im writing this code (and color coding it too ;) ) off the top of my head while at work so it may not be entirely accurate but I tried to make sure it was valid. Any help is much appreciated :)

2 Replies

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19y ago
Ah! Very good! I thought I may have had to implement a "dummy" site to allow testing because thats what the generic list was looking for. I knew I was missing a few things (namely the paremeter-less contructor for the list!) so thanks for putting that stuff in there too.

The whole idea behind this is to try to avoid recasts if at all possible (I have a feeling that theyre dubiously expensive). I want to be able to have the list already filled with precast Site objects so I dont have to have access to the actual Site class in the upper class heirarchy in order to be able to use the items in the list and I can avoid recasts. This will work wonderully!

Thanks :)
0
Alan19y ago
It needed some modification but try this, complete with some (rather silly) test code:

using System;
using System.Collections.Generic;

class Test
{
    static void Main()
    {
       Site s1 = new Site();
       Site s2 = new Site();
       Site s3 = new Site();
       Site s4 = new Site();
       Site s5 = new Site();
       s1.UniqueID = "2";
       s1.Name = "Google";
       s2.UniqueID = "3";
       s2.Name = "C# Corner";
       s3.UniqueID = "1";
       s3.Name = "Microsoft";
       s4.UniqueID = "4";
       s4.Name = "Wikipedia";
       s5.UniqueID = "5";
       s5.Name = "Code Project";

       List sites = new List();
       sites.Add(s1);
       sites.Add(s2);
       sites.Add(s3);
       sites.Add(s4); // note s5 not added
       SiteList sl = new SiteList(sites);
       bool b = sl.IDExists("3");
       if (b)
       {
          Console.WriteLine("C# Corner is in the list");
       }
       else
       {
          Console.WriteLine("C# Corner is not in the list");
       }
       b = sl.IDExists("5");
       if (b)
       {
          Console.WriteLine("Code Project is in the list");
       }
       else
       {
          Console.WriteLine("Code Project is not in the list");
       }
       Console.ReadKey();

    }

}

public class Site : IComparable
{
    private string name;
    private string uniqueID;

    internal string Name
    {
       get { return this.name; }
       set { this.name = value; }
    }
    internal string UniqueID
    {
       get { return this.uniqueID; }
       set { this.uniqueID = value; }
    }

    public int CompareTo(object site)
    {
       return String.Compare(this.uniqueID, ((Site)site).uniqueID);
    }
}

public sealed class SiteList
{
    private List pendingSiteList = new List();

    public bool IDExists(string uniqueID)
    {
       Site site = new Site();
       site.UniqueID = uniqueID;
       int index = pendingSiteList.BinarySearch(site);

       if(index >= 0)
          return true;
       else
          return false;
    }

    public List PendingSiteList
    {
       get { return this.pendingSiteList; }
    }

    public SiteList(List sites)
    {
       sites.Sort(); // needs to be sorted to use BinarySearch
       pendingSiteList = sites;
    }
}
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