Enumerable.Contains Enumerable.Contains Enumerable.Contains Enumerable.Contains Method

定義

判斷序列是否包含指定的項目。Determines whether a sequence contains a specified element.

多載

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

判斷序列是否包含指定的項目,使用預設相等比較子。Determines whether a sequence contains a specified element by using the default equality comparer.

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

判斷序列是否包含指定的項目,使用指定的IEqualityComparer<T>Determines whether a sequence contains a specified element by using a specified IEqualityComparer<T>.

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

判斷序列是否包含指定的項目,使用預設相等比較子。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

類型參數

TSource

source 項目的類型。The type of the elements of source.

參數

source
IEnumerable<TSource>

要在其中尋找值的序列。A sequence in which to locate a value.

value
TSource TSource TSource TSource

要在序列中尋找的值。The value to locate in the sequence.

傳回

true 如果來源序列包含具有指定的值; 的項目否則, falsetrue if the source sequence contains an element that has the specified value; otherwise, false.

例外狀況

範例

下列程式碼範例示範如何使用Contains<TSource>(IEnumerable<TSource>, TSource)來判斷陣列是否包含特定項目。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.
MsgBox("The array " & text & " contain " & fruit)

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

備註

如果類型source會實作ICollection<T>,則Contains中實作的方法會叫用來取得結果。If the type of source implements ICollection<T>, the Contains method in that implementation is invoked to obtain the result. 否則,這個方法會判斷是否source包含指定的項目。Otherwise, this method determines whether source contains the specified element.

只要找到相符的項目,列舉型別就會終止。Enumeration is terminated as soon as a matching element is found.

項目時,會比較指定的值上,使用預設相等比較子, DefaultElements are compared to the specified value by using the default equality comparer, Default.

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

判斷序列是否包含指定的項目,使用指定的IEqualityComparer<T>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

類型參數

TSource

source 項目的類型。The type of the elements of source.

參數

source
IEnumerable<TSource>

要在其中尋找值的序列。A sequence in which to locate a value.

value
TSource TSource TSource TSource

要在序列中尋找的值。The value to locate in the sequence.

comparer
IEqualityComparer<TSource>

用來比較值的相等比較子。An equality comparer to compare values.

傳回

true 如果來源序列包含具有指定的值; 的項目否則, falsetrue if the source sequence contains an element that has the specified value; otherwise, false.

例外狀況

範例

下列範例示範如何實作可用於相等比較子Contains方法。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

實作這個比較子之後,您可以使用一連串Product中的物件Contains方法,如下列範例所示: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

備註

只要找到相符的項目,列舉型別就會終止。Enumeration is terminated as soon as a matching element is found.

如果comparernull,預設的相等比較子, Default,用來比較項目指定的值。If comparer is null, the default equality comparer, Default, is used to compare elements to the specified value.

適用於