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Array.Exists<T> Method

Determines whether the specified array contains elements that match the conditions defined by the specified predicate.

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)

public static bool Exists<T>(
	T[] array,
	Predicate<T> match
)

Type Parameters

T

The type of the elements of the array.

Parameters

array
Type: T[]

The one-dimensional, zero-based Array to search.

match
Type: System.Predicate<T>

The Predicate<T> that defines the conditions of the elements to search for.

Return Value

Type: System.Boolean
true if array contains one or more elements that match the conditions defined by the specified predicate; otherwise, false.

ExceptionCondition
ArgumentNullException

array is null.

-or-

match is null.

The Predicate<T> is a delegate to a method that returns true if the object passed to it matches the conditions defined in the delegate. The elements of array are individually passed to the Predicate<T>, and processing is stopped when a match is found.

NoteNote

In C# and Visual Basic, it is not necessary to create the Predicate<T> delegate explicitly. These languages infer the correct delegate from context and create it automatically.

This method is an O(n) operation, where n is the Length of array.

The following example uses the Exists<T> method to indicate whether any names in a string array begin with a specified character. The example instantiates a StringSearcher object by passing the string to search for to its class constructor. The StringSearcher.StartsWith method has same signature as the Predicate<T> delegate. When the Exists<T> method is called, each member of the array is passed to the delegate until it returns true or iterates all the elements in the array.

using System;

public class Example
{
   public static void Main()
   {
      String[] names = { "Adam", "Adel", "Bridgette", "Carla",
                         "Charles", "Daniel", "Elaine", "Frances",
                         "George", "Gillian", "Henry", "Irving",
                         "James", "Janae", "Lawrence", "Miguel",
                         "Nicole", "Oliver", "Paula", "Robert",
                         "Stephen", "Thomas", "Vanessa",
                         "Veronica", "Wilberforce" };
      Char[] charsToFind = { 'A', 'K', 'W', 'Z' };

      foreach (var charToFind in charsToFind)
         Console.WriteLine("One or more names begin with '{0}': {1}",
                           charToFind,
                           Array.Exists(names, (new StringSearcher(charToFind)).StartsWith));
   }
}

public class StringSearcher
{
   Char firstChar;

   public StringSearcher(Char firstChar)
   {
      this.firstChar = Char.ToUpper(firstChar);
   }

   public bool StartsWith(String s)
   {
      if (String.IsNullOrEmpty(s)) return false;

      if(s.Substring(0, 1).ToUpper() == firstChar.ToString())
         return true;
      else 
         return false;
   }
}
// The example displays the following output: 
//       One or more names begin with 'A': True 
//       One or more names begin with 'K': False 
//       One or more names begin with 'W': True 
//       One or more names begin with 'Z': False

You can also use a lambda expression rather than explicitly define a method whose signature corresponds to that of the delegate. The following example replaces the StringSearcher class and its StartsWith method with a lambda expression.

using System;

public class Example
{
   public static void Main()
   {
      String[] names = { "Adam", "Adel", "Bridgette", "Carla",
                         "Charles", "Daniel", "Elaine", "Frances",
                         "George", "Gillian", "Henry", "Irving",
                         "James", "Janae", "Lawrence", "Miguel",
                         "Nicole", "Oliver", "Paula", "Robert",
                         "Stephen", "Thomas", "Vanessa",
                         "Veronica", "Wilberforce" };
      Char[] charsToFind = { 'A', 'K', 'W', 'Z' };

      foreach (var charToFind in charsToFind)
         Console.WriteLine("One or more names begin with '{0}': {1}",
                           charToFind,
                           Array.Exists(names,
                                        s => { if (String.IsNullOrEmpty(s))
                                                  return false;

                                               if (s.Substring(0, 1).ToUpper() == charToFind.ToString())
                                                  return true;
                                               else 
                                                  return false;
                                             } ));
   }
}
// The example displays the following output: 
//       One or more names begin with 'A': True 
//       One or more names begin with 'K': False 
//       One or more names begin with 'W': True 
//       One or more names begin with 'Z': False
using System;

public class Example
{
   public static void Main()
   {
      String[] names = { "Adam", "Adel", "Bridgette", "Carla",
                         "Charles", "Daniel", "Elaine", "Frances",
                         "George", "Gillian", "Henry", "Irving",
                         "James", "Janae", "Lawrence", "Miguel",
                         "Nicole", "Oliver", "Paula", "Robert",
                         "Stephen", "Thomas", "Vanessa",
                         "Veronica", "Wilberforce" };
      Char[] charsToFind = { 'A', 'K', 'W', 'Z' };

      foreach (var charToFind in charsToFind)
         Console.WriteLine("One or more names begin with '{0}': {1}",
                           charToFind,
                           Array.Exists(names,
                                        s => { if (String.IsNullOrEmpty(s))
                                                  return false;

                                               if (s.Substring(0, 1).ToUpper() == charToFind.ToString())
                                                  return true;
                                               else 
                                                  return false;
                                             } ));
   }
}
// The example displays the following output: 
//       One or more names begin with 'A': True 
//       One or more names begin with 'K': False 
//       One or more names begin with 'W': True 
//       One or more names begin with 'Z': False

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8
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