.net_2.0

Concrete Example: Convert Hashtable to Dictionary (Generics)

This entry will be short and sweet.  After trying to find some kind of guide for converting from Hashtables - to using the generics Dictionary...I wanted to provide a more complex yet simple code comparision.

In this example the first code snippet is the hashtable method.  What this class does is store a requested url as string, and places into the hastable a object that contains all the data to dynamically create the page.

    using System;
    using System.Collections;
    using System.Collections.Specialized;


    //*********************************************************************
    /// Represents a collection of PageInfo objects representing named
    /// pages.
    //*********************************************************************

   
    public class NamedPageCollection : Hashtable {


        //*********************************************************************
        //
        /// Add Method
        //
        /// Adds a new PageInfo object to the collection.
        //
        //*********************************************************************

        override public void Add(Object key, Object value) {
                base[key] = value;
        }



        //*********************************************************************
        //
        /// this Indexer
        //
        /// Returns a PageInfo object.
        //
        //*********************************************************************

        public PageInfo this[string key] {
            get {
                return (PageInfo)base[key];
            }
        }
 
 

        //*********************************************************************
        /// Initializes the Hashtable as case-insensitive.
        //
        //*********************************************************************
     
        public NamedPageCollection() : base(new CaseInsensitiveHashCodeProvider(), new CaseInsensitiveComparer() ) {}
       
    }
}

Here is how you would convert the code above, to use the generics and the  Dictionary<key, value> and not require changing any other code that uses this class and associated methods. 

    using System;
    using System.Collections;
    using System.Collections.Generic; //<- required
    using System.Collections.Specialized;//<-maybe removed
    using System.Web; //added so we can trace the output...

 public class NamedPageCollection
    {

        public Dictionary<string, PageInfo> Dictionary = new Dictionary<string, PageInfo>();
        //*********************************************************************
        //
        // Add Method
        //
        // Adds a new PageInfo object to the collection.
        //
        //*********************************************************************

        public void Add(string key, PageInfo value)
        {
                Dictionary.Add(key.ToLower(), value);
                HttpContext.Current.Trace.Warn("!@!@ - Key added was: <" + key+">");
        }



        //*********************************************************************
        //
        // this Indexer
        //
        // Returns a PageInfo object.
        //
        //*********************************************************************

        public PageInfo this[string key]
        {
            get
            {
                try
                {
                    return Dictionary[key.ToLower()];
                }
                catch
                {
                    HttpContext.Current.Trace.Warn("!@!@ - Key requested was: <" + key + ">");
                    return null;
                }
               
            }
        }
 
 

       
    }
}

 
Note:  There is no flag on the Dictionary for using case insensitive compares - hence why I convert them all to Lower().  Otherwise, if you have "/myURL.aspx" as a key but the search key is "/MYurl.aspx" - not match will be had.  The try... catch is because the Dictionary will throw an exception instead of returning null (unlike the HashTable implementation)... Easy enough - catch the exception and ignore it and return a null.

In conclusion - this is a very simple case illustrating how to convert a class that inherits from the  Hashtable and allows you to convert to use the generic's Dictionary<> instead....