C# | StringDictionary Class

StringDictionary is a specialized collection. This class comes under the System.Collections.Specialized namespace. It only allows string keys and string values. It suffers from performance problems. It implements a hash table with the key and the value strongly typed to be strings rather than objects.

Characteristics:

• A key cannot be null, but a value can.
• The key is handled in a case-insensitive manner i.e, it is translated to lowercase before it is used with the string dictionary.
• The constructor StringDictionary() initializes a new instance of the StringDictionary class.

Constructors

Constructor	Description
StringDictionary()	Initializes a new instance of the StringDictionary class.

Example:

// C# code to create a StringDictionary
using System;
using System.Collections;
using System.Collections.Specialized;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating a StringDictionary named myDict
        StringDictionary myDict = new StringDictionary();

        // Adding key and value into the StringDictionary
        myDict.Add("A", "Apple");
        myDict.Add("B", "Banana");
        myDict.Add("C", "Cat");
        myDict.Add("D", "Dog");
        myDict.Add("E", "Elephant");

        // Displaying the keys and values in StringDictionary
        foreach(DictionaryEntry dic in myDict)
        {
            Console.WriteLine(dic.Key + " " + dic.Value);
        }
    }
}

Output:

d Dog
b Banana
c Cat
e Elephant
a Apple

Properties

Property	Description
Count	Gets the number of key/value pairs in the StringDictionary.
IsSynchronized	Gets a value indicating whether access to the StringDictionary is synchronized (thread safe).
Item[String]	Gets or sets the value associated with the specified key.
Keys	Gets a collection of keys in the StringDictionary.
SyncRoot	Gets an object that can be used to synchronize access to the StringDictionary.
Values	Gets a collection of values in the StringDictionary.

Example:

// C# code illustrate the Properties of
// StringDictionary class
using System;
using System.Collections;
using System.Collections.Specialized;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating a StringDictionary named myDict
        StringDictionary myDict = new StringDictionary();

        // Adding key and value into the StringDictionary
        myDict.Add("3", "prime & odd");
        myDict.Add("2", "prime & even");
        myDict.Add("4", "non-prime & even");
        myDict.Add("9", "non-prime & odd");


        // -------- Values Property --------

        // Getting a collection of values
        // in the StringDictionary
        foreach(string val in myDict.Values)
        {
            Console.WriteLine(val);
        }


        // -------- IsSynchronized Property --------

        // Checking if StringDictionary
        // is synchronized (thread safe)
        Console.WriteLine(myDict.IsSynchronized);
    }
}

Output:

prime & even
prime & odd
non-prime & odd
non-prime & even
False

Methods

Method	Description
Add(String, String)	Adds an entry with the specified key and value into the StringDictionary.
Clear()	Removes all entries from the StringDictionary.
ContainsKey(String)	Determines if the StringDictionary contains a specific key.
ContainsValue(String)	Determines if the StringDictionary contains a specific value.
CopyTo(Array, Int32)	Copies the string dictionary values to a one-dimensional Array instance at the specified index.
Equals(Object)	Determines whether the specified object is equal to the current object.
GetEnumerator()	Returns an enumerator that iterates through the string dictionary.
GetHashCode()	Serves as the default hash function.
GetType()	Gets the Type of the current instance.
MemberwiseClone()	Creates a shallow copy of the current Object.
Remove(String)	Removes the entry with the specified key from the string dictionary.
ToString()	Returns a string that represents the current object.

Example 1:

// C# code to remove the entry
// with the specified key from
// the StringDictionary
using System;
using System.Collections;
using System.Collections.Specialized;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating a StringDictionary named myDict
        StringDictionary myDict = new StringDictionary();

        // Adding key and value into the StringDictionary
        myDict.Add("A", "Apple");
        myDict.Add("B", "Banana");
        myDict.Add("C", "Cat");
        myDict.Add("D", "Dog");
        myDict.Add("E", "Elephant");
        myDict.Add("F", "Fish");

        // Displaying the keys and values in StringDictionary
        Console.WriteLine("The number of key/value pairs are : " + myDict.Count);

        // Removing the entry with the specified
        // key from the StringDictionary
        myDict.Remove("D");

        // Displaying the keys and values in StringDictionary
        Console.WriteLine("The number of key/value pairs are : " + myDict.Count);
    }
}

Output:

The number of key/value pairs are : 6
The number of key/value pairs are : 5

Example 2:

// C# code to copy StringDictionary
// to Array at the specified index
using System;
using System.Collections;
using System.Collections.Specialized;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating a StringDictionary named myDict
        StringDictionary myDict = new StringDictionary();

        // Adding key and value into the StringDictionary
        myDict.Add("A", "Apple");
        myDict.Add("B", "Banana");
        myDict.Add("C", "Cat");
        myDict.Add("D", "Dog");
        myDict.Add("E", "Elephant");

        // Creating an Array named myArr
        DictionaryEntry[] myArr = { new DictionaryEntry(),
                                    new DictionaryEntry(),
                                    new DictionaryEntry(),
                                    new DictionaryEntry(),
                                    new DictionaryEntry() };

        // Copying StringDictionary to
        // Array at the specified index
        myDict.CopyTo(myArr, 0);

        // Displaying key and value pairs in Array myArr
        for (int i = 0; i < myArr.Length; i++) {
            Console.WriteLine(myArr[i].Key + " " + myArr[i].Value);
        }
    }
}

Output:

d Dog
b Banana
c Cat
e Elephant
a Apple

Reference:

• https://docs.microsoft.com/en-us/dotnet/api/system.collections.specialized.stringdictionary?view=netframework-4.7.2