How i loop through my class object add in hashtable object

Question

// this is my class object
Friend f1 = new Friend("Nazir",24);
Friend f2 = new Friend("Hamza", 24);
Friend f3 = new Friend("Abdullah", 23);

Hashtable myhash = new Hashtable();

// add this object in hashtable object
myhash.Add("13b-049-bs",f1);
myhash.Add("13b-034-bs", f1);
myhash.Add("13b-038-bs", f1);

foreach (Friend item in myhash)
{
    Console.WriteLine("Key {0}\tName {1}\tAge {2}",item.Name,item.Age,myhash.Keys);
}

I got this error:

An unhandled exception of type 'System.InvalidCastException' occurred in HashTableDemo.exe

Why are you using the non-typed Hashtable? It would be easier to use a strongly typed Dictionary<string,Friend> - that way you do not have to cast your keys or values. Iterating over it works as well - you'll get stronlgy typed KeyValuePair<string,Friend> via foreach (var kvp in yourDict) that you then can access by kvp.Key and kvp.Value without casting... — Patrick Artner
– Patrick Artner, Commented Dec 5, 2017 at 8:43

Pranay Rana · Accepted Answer · 2017-12-05 07:49:40Z

1

try out , as data store in hash tbale is not type of Friend object youare getting error, if you dont know type than make use of var that will resolve error

  foreach (var  item in myhash)
        {
           string key = de.Key.ToString();
           Friend val  = (Friend) item.Value;
           Console.WriteLine("Key {0}\tName {1}\tAge {2}", key, val.Name, val.Age );
        }

or you can do like this

foreach(DictionaryEntry de in myHashtable)
{
      string key = de.Key.ToString();
   Friend val  = (Friend) de.Value;
   Console.WriteLine("Key {0}\tName {1}\tAge {2}", key, val.Name, val.Age );
}

Read out : Hashtable Class

edited Dec 5, 2017 at 7:49

answered Dec 5, 2017 at 7:33

Pranay Rana

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7 Comments

Pranay Rana Over a year ago

@Rafalon - why its not good practice ...that is leagal way as per language structure ....it introduced with linq for that purpose only ...any ways i updated my answer with DictionaryEntry , hope you like to revert you -1 point

Pranay Rana Over a year ago

@KonstantinChernov - updated that part also ..............i havent seen that ..thanks for pointing it out

Pranay Rana Over a year ago

@Rafalon - it debated many time and using or not using it , is on developer , that what my point , in my coding style i use var ..........why not to use lagnaguge is providing that feature ...i am not adding min there

Syed Nazir Hussain Over a year ago

Error 1 'object' does not contain a definition for 'Key' and no extension method 'Key' accepting a first argument of type 'object' could be found (are you missing a using directive or an assembly reference?) E:\C sharp\UnderstandingCollection\HashTableDemo\Program.cs 26 35 HashTableDemo

Hille Over a year ago

Please wait for 5 min to edit, I'm trying to edit your question for 5 min now, but you canceled it 4 times xD I made some language and code format improvements :)

|

Arash Motamedi · Accepted Answer · 2017-12-05 08:40:03Z

0

The iterator (enumerator) of Hashtable returns objects of type DictionaryEntry. Therefore, in your foreach loop, each item will have two properties: Key and Value, both of type object. You can individually cast the Key and Value properties on each item to your desired type. For example:

foreach (DictionaryEntry item in myhash)
{
    // Cast item.Key to string
    string key = (string)item.Key;

    // And cast item.Value to Friend
    Friend friend = (Friend)item.Value;

    Console.WriteLine("Key {0}\tName {1}\tAge {2}", key, friend.Name, friend.Age);
}

answered Dec 5, 2017 at 8:40

Arash Motamedi

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Comments

Patrick Artner · Accepted Answer · 2017-12-05 08:54:07Z

Use strongly typed Dictionary (using System.Collections.Generic needed):

using System.Collections.Generic;

public class Program
{
    class Friend
    {
        public string Name {get;set;}    
        public int Age {get;set;}

        public Friend(string name, int age)
        {
            Name = name;
            Age = age;
        }
    }

    public static void Main()
    {
        // this is my class object
        Friend f1 = new Friend("Nazir", 24);
        Friend f2 = new Friend("Hamza", 24);
        Friend f3 = new Friend("Abdullah", 23);
        var myDict = new Dictionary<string, Friend>();
        // add this object in hashtable object
        myDict["13b-049-bs"] = f1;
        myDict["13b-034-bs"] = f1;
        myDict["13b-038-bs"] = f1;
        foreach (KeyValuePair<string, Friend> item in myDict)
        {
            Console.WriteLine("Key {0}\tName {1}\tAge {2}", item.Key, item.Value.Name, item.Value.Age);
        }
    }
}

Strongly typed has the advantage that you never will put an Enemy (or some other Type inside this dict - unless it derives from Friend.

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