Enumerable.Contains Method

Definition

确定序列是否包含指定的元素。Determines whether a sequence contains a specified element.

Overloads

Contains<TSource>(IEnumerable<TSource>, TSource)

通过使用默认的相等比较器确定序列是否包含指定的元素。Determines whether a sequence contains a specified element by using the default equality comparer.

Contains<TSource>(IEnumerable<TSource>, TSource, IEqualityComparer<TSource>)

通过使用指定的 IEqualityComparer<T> 确定序列是否包含指定的元素。Determines whether a sequence contains a specified element by using a specified IEqualityComparer<T>.

Contains<TSource>(IEnumerable<TSource>, TSource)

通过使用默认的相等比较器确定序列是否包含指定的元素。Determines whether a sequence contains a specified element by using the default equality comparer.

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

Type Parameters

TSource

source 的元素类型。The type of the elements of source.

Parameters

source
IEnumerable<TSource>

要在其中定位某个值的序列。A sequence in which to locate a value.

value
TSource

要在序列中定位的值。The value to locate in the sequence.

Returns

Boolean

如果源序列包含具有指定值的元素,则为 true;否则为 falsetrue if the source sequence contains an element that has the specified value; otherwise, false.

Exceptions

sourcenullsource is null.

Examples

下面的代码示例演示如何使用 Contains<TSource>(IEnumerable<TSource>, TSource) 来确定数组是否包含特定元素。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

Remarks

如果 source 的类型实现 ICollection<T>,则调用该实现中的 Contains 方法来获取结果。If the type of source implements ICollection<T>, the Contains method in that implementation is invoked to obtain the result. 否则,此方法将确定 source 是否包含指定的元素。Otherwise, this method determines whether source contains the specified element.

如果找到匹配的元素,则枚举将立即终止。Enumeration is terminated as soon as a matching element is found.

通过使用默认的相等比较器 Default,将元素与指定的值进行比较。Elements are compared to the specified value by using the default equality comparer, Default.

Contains<TSource>(IEnumerable<TSource>, TSource, IEqualityComparer<TSource>)

通过使用指定的 IEqualityComparer<T> 确定序列是否包含指定的元素。Determines whether a sequence contains a specified element by using a specified IEqualityComparer<T>.

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);
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

Type Parameters

TSource

source 的元素类型。The type of the elements of source.

Parameters

source
IEnumerable<TSource>

要在其中定位某个值的序列。A sequence in which to locate a value.

value
TSource

要在序列中定位的值。The value to locate in the sequence.

comparer
IEqualityComparer<TSource>

一个对值进行比较的相等比较器。An equality comparer to compare values.

Returns

Boolean

如果源序列包含具有指定值的元素,则为 true;否则为 falsetrue if the source sequence contains an element that has the specified value; otherwise, false.

Exceptions

sourcenullsource is null.

Examples

下面的示例演示如何实现可在 Contains 方法中使用的相等比较器。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

实现此比较器后,你可以在 Contains 方法中使用 Product 对象序列,如以下示例中所示: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

Remarks

如果找到匹配的元素,则枚举将立即终止。Enumeration is terminated as soon as a matching element is found.

如果 null``comparer,则使用默认的相等比较器 Default,将元素与指定值进行比较。If comparer is null, the default equality comparer, Default, is used to compare elements to the specified value.

Applies to