Check if OrderedDictionary collection contains a specific key in C#

The OrderedDictionary collection in C# provides the Contains() method to check if a specific key exists in the collection. This method returns a boolean value − true if the key is found, false otherwise.

Syntax

Following is the syntax for checking if an OrderedDictionary contains a specific key −

bool result = orderedDictionary.Contains(key);

Parameters

• key − The key to locate in the OrderedDictionary collection.

Return Value

The method returns true if the OrderedDictionary contains an element with the specified key; otherwise, false.

Using Contains() with Numeric Keys

Example

using System;
using System.Collections;
using System.Collections.Specialized;

public class Demo {
   public static void Main(){
      OrderedDictionary dict = new OrderedDictionary();
      dict.Add("1", "One");
      dict.Add("2", "Two");
      dict.Add("3", "Three");
      dict.Add("4", "Four");
      dict.Add("5", "Five");
      dict.Add("6", "Six");
      dict.Add("7", "Seven");
      dict.Add("8", "Eight");

      ICollection col = dict.Values;
      String[] strVal = new String[dict.Count];
      col.CopyTo(strVal, 0);
      
      Console.WriteLine("Displaying the values...");
      for (int i = 0; i < dict.Count; i++) {
         Console.WriteLine(strVal[i]);
      }
      
      Console.WriteLine("If OrderedDictionary read-only? = " + dict.IsReadOnly);
      Console.WriteLine("The OrderedDictionary has the key 15? = " + dict.Contains("15"));
      Console.WriteLine("The OrderedDictionary has the key 5? = " + dict.Contains("5"));
   }
}

The output of the above code is −

Displaying the values...
One
Two
Three
Four
Five
Six
Seven
Eight
If OrderedDictionary read-only? = False
The OrderedDictionary has the key 15? = False
The OrderedDictionary has the key 5? = True

Using Contains() with String Keys

Example

using System;
using System.Collections;
using System.Collections.Specialized;

public class Demo {
   public static void Main(){
      OrderedDictionary dict = new OrderedDictionary();
      dict.Add("A", "Pen");
      dict.Add("B", "Pencil");
      dict.Add("C", "Notebook");
      dict.Add("D", "Table");
      dict.Add("E", "Chair");
      dict.Add("F", "Coworking");
      dict.Add("G", "Cubicle");
      dict.Add("H", "Sticky Notes");
      dict.Add("I", "WhiteBoard");
      dict.Add("J", "Marker");

      ICollection col = dict.Values;
      String[] strVal = new String[dict.Count];
      col.CopyTo(strVal, 0);
      
      Console.WriteLine("Displaying the values...");
      for (int i = 0; i < dict.Count; i++) {
         Console.WriteLine(strVal[i]);
      }
      
      Console.WriteLine("If OrderedDictionary read-only? = " + dict.IsReadOnly);
      Console.WriteLine("The OrderedDictionary has the key B? = " + dict.Contains("B"));
      Console.WriteLine("The OrderedDictionary has the key Z? = " + dict.Contains("Z"));
   }
}

The output of the above code is −

Displaying the values...
Pen
Pencil
Notebook
Table
Chair
Coworking
Cubicle
Sticky Notes
WhiteBoard
Marker
If OrderedDictionary read-only? = False
The OrderedDictionary has the key B? = True
The OrderedDictionary has the key Z? = False

Key Features of OrderedDictionary.Contains()

• The method performs key-based lookup, not value-based search.

• Key comparison is case-sensitive for string keys.

• The method has O(n) time complexity as it may need to search through the collection.

• Works with any object type as keys, not just strings.

Conclusion

The Contains() method provides an efficient way to check if a specific key exists in an OrderedDictionary collection. It returns a boolean value indicating the presence of the key, making it useful for conditional operations and validation before accessing dictionary elements.