Check if Hashtable is read-only in C#

The Hashtable class in C# provides the IsReadOnly property to determine whether the hashtable is read-only or allows modifications. A read-only hashtable prevents adding, removing, or modifying elements after creation.

Syntax

Following is the syntax for checking if a Hashtable is read-only −

bool isReadOnly = hashtable.IsReadOnly;

Return Value

The IsReadOnly property returns a bool value −

• true if the Hashtable is read-only

• false if the Hashtable allows modifications

Using IsReadOnly with Standard Hashtable

A standard Hashtable created using the default constructor is not read-only −

using System;
using System.Collections;

public class Demo {
   public static void Main() {
      Hashtable hash = new Hashtable();
      hash.Add("One", "Katie");
      hash.Add("Two", "John");
      hash.Add("Three", "Barry");
      hash.Add("Four", "David");
      hash.Add("Five", "Harry");
      
      Console.WriteLine("Hashtable Key and Value pairs...");
      foreach(DictionaryEntry entry in hash) {
         Console.WriteLine("{0} and {1}", entry.Key, entry.Value);
      }
      
      Console.WriteLine("Is the Hashtable having fixed size? = " + hash.IsFixedSize);
      Console.WriteLine("Is Hashtable read-only? = " + hash.IsReadOnly);
   }
}

The output of the above code is −

Hashtable Key and Value pairs...
One and Katie
Five and Harry
Three and Barry
Two and John
Four and David
Is the Hashtable having fixed size? = False
Is Hashtable read-only? = False

Creating a Read-Only Hashtable

You can create a read-only wrapper around an existing hashtable using Hashtable.ReadOnly() method −

using System;
using System.Collections;

public class Demo {
   public static void Main() {
      Hashtable originalHash = new Hashtable();
      originalHash.Add("1", "A");
      originalHash.Add("2", "B");
      originalHash.Add("3", "C");
      
      // Create a read-only wrapper
      Hashtable readOnlyHash = Hashtable.ReadOnly(originalHash);
      
      Console.WriteLine("Original Hashtable:");
      Console.WriteLine("Is read-only? = " + originalHash.IsReadOnly);
      
      Console.WriteLine("\nRead-only wrapper:");
      Console.WriteLine("Is read-only? = " + readOnlyHash.IsReadOnly);
      
      Console.WriteLine("\nContents of read-only hashtable:");
      foreach(DictionaryEntry entry in readOnlyHash) {
         Console.WriteLine("{0} and {1}", entry.Key, entry.Value);
      }
   }
}

The output of the above code is −

Original Hashtable:
Is read-only? = False

Read-only wrapper:
Is read-only? = True

Contents of read-only hashtable:
1 and A
2 and B
3 and C

Comparison

Conclusion

The IsReadOnly property provides a simple way to check if a Hashtable allows modifications. Standard hashtables return false, while read-only wrappers created using Hashtable.ReadOnly() return true.