Check if two StringDictionary objects are equal or not in C#

The Equals() method for StringDictionary performs reference comparison, meaning it returns true only when both variables point to the same object in memory. Even if two dictionaries contain identical key-value pairs, they will not be considered equal unless they reference the same object.

Using Reference Assignment for Equality

Example

using System;
using System.Collections.Specialized;

public class Demo {
   public static void Main() {
      StringDictionary strDict1 = new StringDictionary();
      strDict1.Add("A", "John");
      strDict1.Add("B", "Andy");
      strDict1.Add("C", "Tim");
      strDict1.Add("D", "Ryan");
      strDict1.Add("E", "Kevin");
      strDict1.Add("F", "Katie");
      strDict1.Add("G", "Brad");
      
      StringDictionary strDict2 = new StringDictionary();
      strDict2.Add("A", "John");
      strDict2.Add("B", "Andy");
      strDict2.Add("C", "Tim");
      strDict2.Add("D", "Ryan");
      strDict2.Add("E", "Kevin");
      strDict2.Add("F", "Katie");
      strDict2.Add("G", "Brad");
      
      StringDictionary strDict3 = new StringDictionary();
      strDict3 = strDict2;
      
      Console.WriteLine("Is Dictionary2 equal to Dictionary3? = " + strDict2.Equals(strDict3));
      Console.WriteLine("Is Dictionary1 equal to Dictionary3? = " + strDict1.Equals(strDict3));
   }
}

The output of the above code is −

Is Dictionary2 equal to Dictionary3? = True
Is Dictionary1 equal to Dictionary2? = False

Content Comparison Between StringDictionaries

The following example demonstrates that even dictionaries with identical content are not considered equal by the default Equals() method −

Example

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

public class Demo {
   public static void Main() {
      StringDictionary strDict1 = new StringDictionary();
      strDict1.Add("A", "John");
      strDict1.Add("B", "Andy");
      strDict1.Add("C", "Tim");
      strDict1.Add("D", "Ryan");
      strDict1.Add("E", "Kevin");
      strDict1.Add("F", "Katie");
      strDict1.Add("G", "Brad");
      
      Console.WriteLine("StringDictionary1 elements...");
      foreach(DictionaryEntry d in strDict1) {
         Console.WriteLine(d.Key + " " + d.Value);
      }
      
      StringDictionary strDict2 = new StringDictionary();
      strDict2.Add("A", "John");
      strDict2.Add("B", "Andy");
      strDict2.Add("C", "Tim");
      strDict2.Add("D", "Ryan");
      strDict2.Add("E", "Kevin");
      strDict2.Add("F", "Katie");
      strDict2.Add("G", "Brad");
      
      Console.WriteLine("\nStringDictionary2 elements...");
      foreach(DictionaryEntry d in strDict2) {
         Console.WriteLine(d.Key + " " + d.Value);
      }
      
      Console.WriteLine("\nIs Dictionary2 equal to Dictionary1? = " + strDict2.Equals(strDict1));
   }
}

The output of the above code is −

StringDictionary1 elements...
a John
b Andy
c Tim
d Ryan
e Kevin
f Katie
g Brad

StringDictionary2 elements...
a John
b Andy
c Tim
d Ryan
e Kevin
f Katie
g Brad

Is Dictionary2 equal to Dictionary1? = False

Custom Content Equality Method

To check if two StringDictionary objects have the same content, you need to implement custom comparison logic −

Example

using System;
using System.Collections.Specialized;

public class Demo {
   public static bool AreEqual(StringDictionary dict1, StringDictionary dict2) {
      if (dict1.Count != dict2.Count) return false;
      
      foreach (string key in dict1.Keys) {
         if (!dict2.ContainsKey(key) || dict1[key] != dict2[key])
            return false;
      }
      return true;
   }
   
   public static void Main() {
      StringDictionary strDict1 = new StringDictionary();
      strDict1.Add("A", "John");
      strDict1.Add("B", "Andy");
      strDict1.Add("C", "Tim");
      
      StringDictionary strDict2 = new StringDictionary();
      strDict2.Add("A", "John");
      strDict2.Add("B", "Andy");
      strDict2.Add("C", "Tim");
      
      Console.WriteLine("Reference equality: " + strDict1.Equals(strDict2));
      Console.WriteLine("Content equality: " + AreEqual(strDict1, strDict2));
   }
}

The output of the above code is −

Reference equality: False
Content equality: True

Conclusion

The Equals() method for StringDictionary performs reference comparison, not content comparison. Two dictionaries with identical key-value pairs will return false unless they reference the same object. For content-based equality checking, implement custom comparison logic that iterates through keys and values.