Enumerable.Contains Methode

public:
generic <typename TSource>
[System::Runtime::CompilerServices::Extension]
 static bool Contains(System::Collections::Generic::IEnumerable<TSource> ^ source, TSource value);

public static bool Contains<TSource> (this System.Collections.Generic.IEnumerable<TSource> source, TSource value);

static member Contains : seq<'Source> * 'Source -> bool

<Extension()>
Public Function Contains(Of TSource) (source As IEnumerable(Of TSource), value As TSource) As Boolean

Typparameter

Parameter

Gibt zurück

Boolean

true, wenn die Quellsequenz ein Element mit dem angegebenen Wert enthält, andernfalls false.true if the source sequence contains an element that has the specified value; otherwise, false.

Ausnahmen

Beispiele

Im folgenden Codebeispiel wird veranschaulicht, wie verwendet wird, Contains<TSource>(IEnumerable<TSource>, TSource) um zu bestimmen, ob ein Array ein bestimmtes Element enthält.The following code example demonstrates how to use Contains<TSource>(IEnumerable<TSource>, TSource) to determine whether an array contains a specific element.

string[] fruits = { "apple", "banana", "mango", "orange", "passionfruit", "grape" };

string fruit = "mango";

bool hasMango = fruits.Contains(fruit);

Console.WriteLine(
    "The array {0} contain '{1}'.",
    hasMango ? "does" : "does not",
    fruit);

// This code produces the following output:
//
// The array does contain 'mango'.

' Create an array of strings.
Dim fruits() As String = {"apple", "banana", "mango", "orange", "passionfruit", "grape"}

' This is the string to search the array for.
Dim fruit As String = "mango"

' Determine if the array contains the specified string.
Dim hasMango As Boolean = fruits.Contains(fruit)

Dim text As String = IIf(hasMango, "does", "does not")

' Display the output.
Console.WriteLine($"The array {text} contain {fruit}")

' This code produces the following output:
'
' The array does contain mango

Hinweise

Wenn der Typ von source implementiert ICollection<T> , wird die- Contains Methode in dieser Implementierung aufgerufen, um das Ergebnis zu erhalten.If the type of source implements ICollection<T>, the Contains method in that implementation is invoked to obtain the result. Andernfalls bestimmt diese Methode, ob source das angegebene Element enthält.Otherwise, this method determines whether source contains the specified element.

Die Enumeration wird beendet, sobald ein entsprechendes Element gefunden wurde.Enumeration is terminated as soon as a matching element is found.

Elemente werden mit dem angegebenen Wert verglichen, indem der Standard Gleichheits Vergleich verwendet wird Default .Elements are compared to the specified value by using the default equality comparer, Default.

public:
generic <typename TSource>
[System::Runtime::CompilerServices::Extension]
 static bool Contains(System::Collections::Generic::IEnumerable<TSource> ^ source, TSource value, System::Collections::Generic::IEqualityComparer<TSource> ^ comparer);

public static bool Contains<TSource> (this System.Collections.Generic.IEnumerable<TSource> source, TSource value, System.Collections.Generic.IEqualityComparer<TSource> comparer);

public static bool Contains<TSource> (this System.Collections.Generic.IEnumerable<TSource> source, TSource value, System.Collections.Generic.IEqualityComparer<TSource>? comparer);

static member Contains : seq<'Source> * 'Source * System.Collections.Generic.IEqualityComparer<'Source> -> bool

<Extension()>
Public Function Contains(Of TSource) (source As IEnumerable(Of TSource), value As TSource, comparer As IEqualityComparer(Of TSource)) As Boolean

Typparameter

Parameter

Gibt zurück

Boolean

true, wenn die Quellsequenz ein Element mit dem angegebenen Wert enthält, andernfalls false.true if the source sequence contains an element that has the specified value; otherwise, false.

Ausnahmen

Beispiele

Im folgenden Beispiel wird gezeigt, wie ein Gleichheits Vergleich implementiert wird, der in der-Methode verwendet werden kann Contains .The following example shows how to implement an equality comparer that can be used in the Contains method.

public class Product
{
    public string Name { get; set; }
    public int Code { get; set; }
}

// Custom comparer for the Product class
class ProductComparer : IEqualityComparer<Product>
{
    // Products are equal if their names and product numbers are equal.
    public bool Equals(Product x, Product y)
    {

        //Check whether the compared objects reference the same data.
        if (Object.ReferenceEquals(x, y)) return true;

        //Check whether any of the compared objects is null.
        if (Object.ReferenceEquals(x, null) || Object.ReferenceEquals(y, null))
            return false;

        //Check whether the products' properties are equal.
        return x.Code == y.Code && x.Name == y.Name;
    }

    // If Equals() returns true for a pair of objects
    // then GetHashCode() must return the same value for these objects.

    public int GetHashCode(Product product)
    {
        //Check whether the object is null
        if (Object.ReferenceEquals(product, null)) return 0;

        //Get hash code for the Name field if it is not null.
        int hashProductName = product.Name == null ? 0 : product.Name.GetHashCode();

        //Get hash code for the Code field.
        int hashProductCode = product.Code.GetHashCode();

        //Calculate the hash code for the product.
        return hashProductName ^ hashProductCode;
    }
}

Public Class Product
    Public Property Name As String
    Public Property Code As Integer
End Class

' Custom comparer for the Product class
Public Class ProductComparer
    Implements IEqualityComparer(Of Product)

    Public Function Equals1(
        ByVal x As Product, 
        ByVal y As Product
        ) As Boolean Implements IEqualityComparer(Of Product).Equals

        ' Check whether the compared objects reference the same data.
        If x Is y Then Return True

        'Check whether any of the compared objects is null.
        If x Is Nothing OrElse y Is Nothing Then Return False

        ' Check whether the products' properties are equal.
        Return (x.Code = y.Code) AndAlso (x.Name = y.Name)
    End Function

    Public Function GetHashCode1(
        ByVal product As Product
        ) As Integer Implements IEqualityComparer(Of Product).GetHashCode

        ' Check whether the object is null.
        If product Is Nothing Then Return 0

        ' Get hash code for the Name field if it is not null.
        Dim hashProductName = 
            If(product.Name Is Nothing, 0, product.Name.GetHashCode())

        ' Get hash code for the Code field.
        Dim hashProductCode = product.Code.GetHashCode()

        ' Calculate the hash code for the product.
        Return hashProductName Xor hashProductCode
    End Function
End Class

Nachdem Sie diesen Vergleich implementiert haben, können Sie eine Sequenz von- Product Objekten in der- Contains Methode verwenden, wie im folgenden Beispiel gezeigt:After you implement this comparer, you can use a sequence of Product objects in the Contains method, as shown in the following example:

Product[] fruits = { new Product { Name = "apple", Code = 9 },
                       new Product { Name = "orange", Code = 4 },
                       new Product { Name = "lemon", Code = 12 } };

Product apple = new Product { Name = "apple", Code = 9 };
Product kiwi = new Product {Name = "kiwi", Code = 8 };

ProductComparer prodc = new ProductComparer();

bool hasApple = fruits.Contains(apple, prodc);
bool hasKiwi = fruits.Contains(kiwi, prodc);

Console.WriteLine("Apple? " + hasApple);
Console.WriteLine("Kiwi? " + hasKiwi);

/*
    This code produces the following output:

    Apple? True
    Kiwi? False
*/

Dim fruits() As Product = 
   {New Product With {.Name = "apple", .Code = 9}, 
    New Product With {.Name = "orange", .Code = 4}, 
    New Product With {.Name = "lemon", .Code = 12}}

Dim apple = New Product With {.Name = "apple", .Code = 9}
Dim kiwi = New Product With {.Name = "kiwi", .Code = 8}

Dim prodc As New ProductComparer()

Dim hasApple = fruits.Contains(apple, prodc)
Dim hasKiwi = fruits.Contains(kiwi, prodc)

Console.WriteLine("Apple? " & hasApple)
Console.WriteLine("Kiwi? " & hasKiwi)


' This code produces the following output:
'
' Apple? True
' Kiwi? False

Hinweise

Die Enumeration wird beendet, sobald ein entsprechendes Element gefunden wurde.Enumeration is terminated as soon as a matching element is found.

Wenn comparer null den Wert hat, wird der Standard Gleichheits Vergleich Default verwendet, um Elemente mit dem angegebenen Wert zu vergleichen.If comparer is null, the default equality comparer, Default, is used to compare elements to the specified value.