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C# | Check if ListDictionary contains a specific key

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ListDictionary.Contains(Object) method is used to check whether the ListDictionary contains a specific key or not. Syntax:
public bool Contains (object key);
Here, key is the key to locate in the ListDictionary. Return Value: The method returns true if the ListDictionary contains an entry with the specified key, otherwise it returns false. Exception: This method will give ArgumentNullException if the key is null. Below given are some examples to understand the implementation in a better way: Example 1:
// C# code to check if ListDictionary
// contains a specific key
using System;
using System.Collections;
using System.Collections.Specialized;
  
class GFG {
  
    // Driver code
    public static void Main()
    {
  
        // Creating a ListDictionary named myDict
        ListDictionary myDict = new ListDictionary();
  
        myDict.Add("Australia", "Canberra");
        myDict.Add("Belgium", "Brussels");
        myDict.Add("Netherlands", "Amsterdam");
        myDict.Add("China", "Beijing");
        myDict.Add("Russia", "Moscow");
        myDict.Add("India", "New Delhi");
  
        // Checking if ListDictionary contains
        // the key "Brazil"
        Console.WriteLine(myDict.Contains("Brazil"));
    }
}

                    
Output:
False
Example 2:
// C# code to check if ListDictionary
// contains a specific key
using System;
using System.Collections;
using System.Collections.Specialized;
  
class GFG {
  
    // Driver code
    public static void Main()
    {
  
        // Creating a ListDictionary named myDict
        ListDictionary myDict = new ListDictionary();
  
        myDict.Add("Australia", "Canberra");
        myDict.Add("Belgium", "Brussels");
        myDict.Add("Netherlands", "Amsterdam");
        myDict.Add("China", "Beijing");
        myDict.Add("Russia", "Moscow");
        myDict.Add("India", "New Delhi");
  
        // Checking if ListDictionary contains
        // the key "null". This should raise
        // "ArgumentNullException" as the key is null
        Console.WriteLine(myDict.Contains(null));
    }
}

                    
Runtime Error:
Unhandled Exception: System.ArgumentNullException: Key cannot be null. Parameter name: key
Note: This method is an O(n) operation, where n is Count. Reference:

Last Updated : 01 Feb, 2019
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