.NET Dictionary as a Property

Question

Can someone point me out to some C# code examples or provide some code, where a Dictionary has been used as a property for a Class.

The examples I have seen so far don't cover all the aspects viz how to declare the dictionary as property, add, remove, and retrieve the elements from the dictionary.

Solution 1

Here's a quick example

class Example {
  private Dictionary<int,string> _map;
  public Dictionary<int,string> Map { get { return _map; } }
  public Example() { _map = new Dictionary<int,string>(); }
}

Some use cases

var e = new Example();
e.Map[42] = "The Answer";

Solution 2

sample code:

public class MyClass
{
  public MyClass()
  {
    TheDictionary = new Dictionary<int, string>();
  }

  // private setter so no-one can change the dictionary itself
  // so create it in the constructor
  public IDictionary<int, string> TheDictionary { get; private set; }
}

sample usage:

MyClass mc = new MyClass();

mc.TheDictionary.Add(1, "one");
mc.TheDictionary.Add(2, "two");
mc.TheDictionary.Add(3, "three");

Console.WriteLine(mc.TheDictionary[2]);

EDIT

When you use C# version 6 or later, you can also use this:

public class MyClass
{
  // you don't need a constructor for this feature

  // no (public) setter so no-one can change the dictionary itself
  // it is set when creating a new instance of MyClass
  public IDictionary<int, string> TheDictionary { get; } = new Dictionary<int, string>();
}

Solution 3

You could also look into indexers. (official MSDN documentation here)

class MyClass
{
    private Dictionary<string, string> data = new Dictionary<string, string>();

    public MyClass()
    {
        data.Add("Turing, Alan", "Alan Mathison Turing, OBE, FRS (pronounced /ˈtjʊ(ə)rɪŋ/) (23 June, 1912 – 7 June, 1954) was a British mathematician, logician, cryptanalyst and computer scientist.")
        //Courtesy of [Wikipedia][3]. Used without permission
    }

    public string this [string index]
    {
        get
        {
            return data[index];
        }
    }
}

Then, once you have populated the dictionary internally, you can access it's information by going

MyClass myExample = new MyClass();

string turingBio = myExample["Turing, Alan"];

EDIT

Obviously, this has to be used carefully, because MyClass is NOT a dictionary, and you cannot use any dictionary methods on it unless you implement them for the wrapper class. But indexers are a great tool in certain situations.

Solution 4

In order to ensure the encapsulation is correct and the dictionary cannot be updated outside the class using Add or the form ExampleDictionary[1]= "test", use IReadOnlyDictionary.

public class Example
{
    private Dictionary<int, string> exampleDictionary;

    public Example() 
    { 
        exampleDictionary = new Dictionary<int, string>(); 
    }

    public IReadOnlyDictionary<int, string> ExampleDictionary
    {
        get { return (IReadOnlyDictionary<int, string>)exampleDictionary; }
    }
}

The following code will not work, which is not the case if IDictionary is used:

var example = new Example();
example.ExampleDictionary[1] = test;

Solution 5

Another example of using a dictionary as a static property with only the get accessor:

  private static Dictionary <string, string> dict = new  Dictionary   <string,string>(){            
            {"Design Matrix", "Design Case"},
            {"N/A", "Other"}
    };


    public static Dictionary <string, string> Dict
    {
        get { return dict}
    }          

This structure can be used to replace values.

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