Array.Exists<T>(T[], Predicate<T>) Method

Definition

Určuje, zda zadané pole obsahuje prvky, které odpovídají podmínkám definovaným zadaným predikátem.Determines whether the specified array contains elements that match the conditions defined by the specified predicate.

public:
generic <typename T>
 static bool Exists(cli::array <T> ^ array, Predicate<T> ^ match);
public static bool Exists<T> (T[] array, Predicate<T> match);
static member Exists : 'T[] * Predicate<'T> -> bool
Public Shared Function Exists(Of T) (array As T(), match As Predicate(Of T)) As Boolean

Type Parameters

T

Typ prvků pole.The type of the elements of the array.

Parameters

array
T[]

Jednorozměrné Array založené na nule pro hledání.The one-dimensional, zero-based Array to search.

match
Predicate<T>

Predicate<T> definující podmínky prvků, které se mají hledat.The Predicate<T> that defines the conditions of the elements to search for.

Returns

Boolean

true, pokud array obsahuje jeden nebo více prvků, které splňují podmínky definované zadaným predikátem; v opačném případě false.true if array contains one or more elements that match the conditions defined by the specified predicate; otherwise, false.

Exceptions

array je null.array is null.

-nebo--or- match je null.match is null.

Examples

Následující příklad určuje podmínky shody pro metodu Exists pomocí výrazů lambda ke kontrole, zda globálním začíná zadaným písmenem nebo zda je v daném poli Nalezeno globálním.The following example specifies the match conditions for the Exists method using lambda expressions to check whether a planet starts with a given letter or whether the planet is found on the given array.

using System;

namespace Example
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] planets = { "Mercury", "Venus",
                "Earth", "Mars", "Jupiter",
                "Saturn", "Uranus", "Neptune" };

            Console.WriteLine("One or more planets begin with 'M': {0}",
                Array.Exists(planets, element => element.StartsWith("M")));

            Console.WriteLine("One or more planets begin with 'T': {0}",
                Array.Exists(planets, element => element.StartsWith("T")));

            Console.WriteLine("Is Pluto one of the planets? {0}",
                Array.Exists(planets, element => element == "Pluto"));
        }
    }
}
// The example displays the following output:
//       One or more planets begin with 'M': True
//       One or more planets begin with 'T': False
//       Is Pluto one of the planets? False
Module Example
    Public Sub Main()
        Dim planets() As String = {"Mercury", "Venus",
                                    "Earth", "Mars", "Jupiter",
                                    "Saturn", "Uranus", "Neptune"}

        Console.WriteLine("One or more planets begin with 'M': {0}",
            Array.Exists(planets, Function(element)
                                      Return element.StartsWith("M")
                                  End Function))

        Console.WriteLine("One or more planets begin with 'T': {0}",
            Array.Exists(planets, Function(element)
                                      Return element.StartsWith("T")
                                  End Function))

        Console.WriteLine("Is Pluto one of the planets? {0}",
            Array.Exists(planets, Function(element)
                                      Return element.Equals("Pluto")
                                  End Function))

    End Sub
End Module
' The example displays the following output:
'       One or more planets begin with 'M': True
'       One or more planets begin with 'T': False
'       Is Pluto one of the planets? False

Následující příklad používá metodu Exists k označení, zda jakékoli názvy v poli řetězce začínají zadaným znakem.The following example uses the Exists method to indicate whether any names in a string array begin with a specified character. Příklad vytvoří instanci objektu StringSearcher předáním řetězce, který se má vyhledat do konstruktoru třídy.The example instantiates a StringSearcher object by passing the string to search for to its class constructor. Metoda StringSearcher.StartsWith má stejný podpis jako delegát Predicate<T>.The StringSearcher.StartsWith method has same signature as the Predicate<T> delegate. Když je volána metoda Exists, je každý člen pole předán delegátovi, dokud nevrátí true nebo neprojde všechny prvky v poli.When the Exists 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
Module Example
   Public Sub Main()
      Dim names() As String = { "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" }
      Dim charsToFind() As Char = { "A"c, "K"c, "W"c, "Z"c }
      
      For Each charToFind In charsToFind
         Console.WriteLine("One or more names begin with '{0}': {1}",
                           charToFind,
                           Array.Exists(names, AddressOf (New StringSearcher(charToFind)).StartsWith))
      Next
   End Sub
   
End Module

Public Class StringSearcher
   Dim firstChar As Char
   
   Public Sub New(firstChar As Char)
      Me.firstChar = Char.ToUpper(firstChar)
   End Sub
   
   Public Function StartsWith(s As String) As Boolean
      If String.IsNullOrEmpty(s) Then Return False
      
      If s.Substring(0, 1).ToUpper = firstChar Then
         Return True
      Else
         Return False
      End If
   End Function
End Class
' 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

Můžete také použít výraz lambda namísto explicitního definování metody, jejíž signatura odpovídá delegátovi.You can also use a lambda expression rather than explicitly define a method whose signature corresponds to that of the delegate. Následující příklad nahrazuje třídu StringSearcher a její StartsWith metoda pomocí výrazu lambda.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
Module Example
   Public Sub Main()
      Dim names() As String = { "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" }
      Dim charsToFind() As Char = { "A"c, "K"c, "W"c, "Z"c }

      For Each charToFind In charsToFind
         Console.WriteLine("One or more names begin with '{0}': {1}",
                           charToFind,
                           Array.Exists(names, Function(s)
                                                  If String.IsNullOrEmpty(s) Then Return False

                                                  If s.Substring(0, 1).ToUpper = charToFind Then
                                                     Return True
                                                  Else
                                                     Return False
                                                  End If
                                               End Function ))
      Next
   End Sub
End Module
' 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

Remarks

Predicate<T> je delegát metody, která vrací true, pokud předaný objekt odpovídá podmínkám definovaným v delegátovi.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. Prvky array jsou jednotlivě předány do Predicate<T>a zpracování je zastaveno, když je nalezena shoda.The elements of array are individually passed to the Predicate<T>, and processing is stopped when a match is found.

Note

V C# a Visual Basic není nutné Predicate<T> delegáta explicitně vytvořit.In C# and Visual Basic, it is not necessary to create the Predicate<T> delegate explicitly. Tyto jazyky odvozují správného delegáta z kontextu a vytvoří jej automaticky.These languages infer the correct delegate from context and create it automatically.

Tato metoda je operace O (n), kde n je Length array.This method is an O(n) operation, where n is the Length of array.

Applies to

See also