Using properties with dictionary

Question

Hi there,

I'm trying to retrieve an objects content based on a key in a dictionary, but don't know how to use the properties in combination with the dictionary. First of all, I create the dictionary and add 5 keys. Each keys value is an object of another class I've created: the Person class. Two parametres (username and password respectively) are passed and stored using properties. How do I retrieve one object and its content based on its key?

Program class:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Collections;

namespace Lagerprojekt_final
{
    class Program
    {
        static void Main(string[] args)
        {
            Dictionary<string, object> d = new Dictionary<string, object>();
            d.Add("kunde1", new Person("kunde1", "pass1"));
            d.Add("kunde2", new Person("kunde2", "pass2"));
            d.Add("kunde3", new Person("kunde3", "pass3"));
            d.Add("kunde4", new Person("kunde4", "pass4"));
            d.Add("admin", new Person("admin", "adminpass"));

            Person kunde1 = new Person();

            // See if Dictionary contains this string
            if (d.ContainsKey("kunde1")) // True
            {

                string v = Convert.ToString(d["kunde1"]);
                Console.WriteLine("Kunde1 Password: {0}", kunde1.Password);
            }

            Console.ReadLine();                                        
          
        }
    }
}

Person class:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Collections;

namespace Lagerprojekt_final
{
    class Person
    {
        protected string brugernavn;
        protected string password;


        //Default constructor
        public Person()
        {
        }

        //Overload method which takes two parameters
        public Person(string brugernavn, string password)
        {
            this.brugernavn = brugernavn;
            this.password = password;
        }

        public string Brugernavn
        {
            set
            { brugernavn = value; }
            get
            { return brugernavn; }

        }

        public string Password
        {
            set
            { password = value; }
            get
            { return password; }

        }

    }
}

Regards,
Anders

Answer 1

Hi,

Declare your dictionary like below. Use Person as value type instead of object.

That might solve your problem.

Dictionary<string, Person> d = new Dictionary<string, Person>();

Then you can access password by d["kunde1"].Password

Answer 2

Hi Tamer Oz,

Thanks for your quick answer. However, I'm not sure if I understand it? Isn't it possible to do like I did with some small additions? If not, can you then elaborate a bit on your code?

Thank you,
Anders

Answer 3

Hi,

Change your code like below.

namespace Lagerprojekt_final
{
    class Program
    {
        static void Main(string[] args)
        {
            Dictionary<string, Person> d = new Dictionary<string, Person>();//this line changed
            d.Add("kunde1", new Person("kunde1", "pass1"));
            d.Add("kunde2", new Person("kunde2", "pass2"));
            d.Add("kunde3", new Person("kunde3", "pass3"));
            d.Add("kunde4", new Person("kunde4", "pass4"));
            d.Add("admin", new Person("admin", "adminpass"));

            Person kunde1 = new Person();

            // See if Dictionary contains this string
            if (d.ContainsKey("kunde1")) // True
            {

                string v = Convert.ToString(d["kunde1"]);
                Console.WriteLine("Kunde1 Password: {0}", d["kunde1"].Password);//this line changed
            }

            Console.ReadLine();                                        
          
        }
    }
}

Answer 4

Works like a charm, thanks!

But I'm not sure why it works ;-) Can you explain the difference between using the Person object as a value type instead of an object?

Regards,
Anders

Answer 5

By using Person you can directly access Person object's properties. Because by passing Person type as generic you say the dictionary that field holds Person type.

And if you type object Dictionary does not know whats the type and it can not cast it. Since object does not have property like password if you want to use properties of person you have to cast it to person manually.

For example

If you use object you can add Person for the first value, and string for the second, and int for the third. That means it holds multiple types and does not know what's the type. However if you use Person, you can only add person object. So it knows the value is person and you can access it's properties.

Answer 6

Aha, the missing link for me was generic types. When would it be an advantage to use object instead of generic type?

Answer 7

When if you are not sure about the type or you want to store different types. Example. If you use object you can add Person for the first value, and string for the second, and int for the third. That means it holds multiple types and does not know what's the type.

Answer 8

I mean, it seems like generic types are a much better than object, so when would it be better to use object?

Answer 9

This is a sample to tell when using object is better.

I don't prefeer to use object as generic.

The advantages and disadvantages is similar to use object intstead a type.

Here is a sample. You can't store all these types in a generic list other than object.

 

List<object> o = new List<object>();

o.Add(1);

o.Add(

"Sample");

o.Add(

Image.FromFile(""));