C# | Check if ListDictionary contains a specific key
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:
- https://docs.microsoft.com/en-us/dotnet/api/system.collections.specialized.listdictionary.contains?view=netframework-4.7.2