Key value pairs pop up everywhere in C# code, and yet after twenty years of being a software developer I still find myself Googling ‘C# how to get a value from a key value pair‘ on a regular basis whenever I am working with a C# Dictionary. I like writing posts about things I can’t remember because every once in a while I Google something and the answer is provided by a post I wrote in the past… which is a lovely feeling! In this post I’ll start by explaining how to initialize a C# Dictionary.
Table of contents
How to initialize a C# Dictionary
Firstly you need to initialize a Dictionary and put some data in it – and in this post I’ll be talking about a dictionary of drinks data, to create a drinks order 🙂 Please note, I’ve also written a similar post but using a C# List instead of a Dictionary.
We initialize a Dictionary where the key is an integer and the value is a string :
using System.Collections.Generic;
Dictionary<int, string> drinksOrder = new Dictionary<int, string>()
{
{ 100, "Lemonade"},
{ 203, "Gin and tonic" },
{ 145, "Small white wine"},
{ 701, "Coke" },
{ 361, "Orange juice" }
};
How to add to a C# Dictionary
To add another key value pair to the Dictionary :
drinksOrder.Add(487, "Sparkling water");
C# Dictionary get value from a key value pair
To get a value from the Dictionary using the key, is as simple as using the pattern dictionaryName[key], so in this case to get the value “Orange juice” out of the Dictionary we would use this code:
//get value out using the key
var drinkValue = drinksOrder[361];
//now write this to the console
Console.WriteLine("Get Drink using key > " + drinkValue);
//this prints -
Get Drink using key > Orange juice
However in reality you need to add a little more code to deal with what happens if the key does not exist in the Dictionary – in the code above, an error will be thrown. This is how to check if it exists first:
//check if the Dictionary contains the key
if (barOrder.ContainsKey(361))
{
//it dies exist, so we can safely use the value
selectedDrink = barOrder[361];
}So in a C# dictionary to get a value by key you first check if the Dictionary contains the key, and then you get the value.
How to convert a Dictionary Key Value pair into JSON
If you want to serialize your Dictionary into json, or a key value pair into json, you need to use the Newtonsoft Nuget package like this:
using Newtonsoft.Json; var json = JsonConvert.SerializeObject(barOrder);
I’ve put together a simple Console app that uses much of this code refactored into stand alone methods. It includes examples of how to :
- Initialize a Dictionary
- Add an item to a Dictionary
- Remove an item from a Dictionary
- Clear a Dictionary
- Convert a Dictionary to json
using Newtonsoft.Json;
using System;
using System.Collections.Generic;
namespace ConsoleApp
{
class Program
{
static void Main(string[] args)
{
//create the initial drinks order
var barOrder = InitializeDictionary();
WriteDictionary(barOrder);
//someone cancels their drink
Console.WriteLine("\nRemove drink by key ....");
barOrder.Remove(145);
//write the order again
WriteDictionary(barOrder);
//someone wants to add a couple of drinks to the order
AddDrinks(barOrder);
WriteDictionary(barOrder);
//checks if the Dictionary contains certain keys, and gets the
//value if it does
CheckDrinks(barOrder);
WaitForKeyPress();
//converts the dictionary to json
Console.WriteLine("\nConvert the order to json ....");
var json = JsonConvert.SerializeObject(barOrder);
Console.WriteLine(json);
//now clear the order because we are finished
Console.WriteLine("\nNow clear the order because is's complete....");
barOrder.Clear();
//write the order again
WriteDictionary(barOrder);
}
private static void WaitForKeyPress()
{
Console.WriteLine("Press any key to continue....");
Console.ReadKey();
}
private static Dictionary<int,string> InitializeDictionary()
{
Dictionary<int, string> drinksOrder = new Dictionary<int, string>()
{
{ 100, "Lemonade"},
{ 203, "Gin and tonic" },
{ 145, "Small white wine"},
{ 701, "Coke" },
{ 361, "Orange juice" }
};
Console.WriteLine("Drinks order created - Dictionary initialized.");
return drinksOrder;
}
private static void CheckDrinks(Dictionary<int, string> barOrder)
{
Console.WriteLine("\n\nCheck if certain drinks exist in the order, using the drinks name....\n");
//someone wants to know if their Coke is in the order, so we need to check
if (barOrder.ContainsValue("Coke"))
{
Console.WriteLine("There's a Coke in the order.");
}
else
{
Console.WriteLine("There's no Coke in the order.");
}
if (barOrder.ContainsValue("Wine"))
{
Console.WriteLine("There's a Wine in the order.");
}
else
{
Console.WriteLine("There's no Wine in the order.");
}
Console.WriteLine("\n\nNow check if a certain drink is in the order...");
string selectedDrink = "No drink found";
//check drink reference
if (barOrder.ContainsKey(361))
{
selectedDrink = barOrder[361];
}
Console.WriteLine("Get Drink using key > " + selectedDrink);
Console.WriteLine("\n");
}
private static void WriteDictionary(Dictionary<int, string> list)
{
Console.WriteLine("\n****** BAR ORDER ******");
foreach (var item in list)
{
Console.WriteLine(item.Key + ": " + item.Value);
}
if (list.Count == 0)
{
Console.WriteLine("---This order is empty---");
}
Console.WriteLine("--------------------------\n");
WaitForKeyPress();
}
private static void AddDrinks(Dictionary<int,string> bardrinks)
{
Console.WriteLine("Add two drinks to the order.....");
bardrinks.Add(487, "Sparkling water");
bardrinks.Add(925, "Prosecco");
}
}
}
Summary
Now you know how to get or add a C# keyvalue pair, initialize a Dictionary, convert it to JSON, you can see how useful they are.