Enumerable.Contains 方法

參考

定義

命名空間:: System.Linq

組件:: System.Linq.dll

組件:: System.Core.dll

組件:: netstandard.dll

重要

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判斷序列是否包含指定的項目。

多載

Contains<TSource>(IEnumerable<TSource>, TSource)	使用預設的相等比較子 (Comparer) 來判斷序列是否包含指定的項目。
Contains<TSource>(IEnumerable<TSource>, TSource, IEqualityComparer<TSource>)	使用指定的 IEqualityComparer<T> 來判斷序列是否包含指定的項目。

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

來源:: Contains.cs

來源:: Contains.cs

來源:: Contains.cs

使用預設的相等比較子 (Comparer) 來判斷序列是否包含指定的項目。

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。

參數

source: IEnumerable<TSource>

要在其中尋找值的序列。

value: TSource

要在序列中尋找的值。

傳回

Boolean

如果來源序列包含具有指定值的項目，則為 true，否則為 false。

例外狀況

ArgumentNullException

source 為 null。

範例

下列程式代碼範例示範如何使用 Contains<TSource>(IEnumerable<TSource>, TSource) 來判斷數位語列是否包含特定專案。

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

備註

如果的型別實作 sourceICollection<T>，則會 Contains 叫用該實作中的方法以取得結果。否則，這個方法會判斷是否 source 包含指定的專案。

一旦找到相符的專案，列舉就會終止。

使用預設相等比較子 Default，將專案與指定的值進行比較。

適用於

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

來源:: Contains.cs

來源:: Contains.cs

來源:: Contains.cs

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

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

類型參數

TSource

source 項目的類型。

參數

source: IEnumerable<TSource>

要在其中尋找值的序列。

value: TSource

要在序列中尋找的值。

comparer: IEqualityComparer<TSource>

用來比較值的相等比較子。

傳回

Boolean

如果來源序列包含具有指定值的項目，則為 true，否則為 false。

例外狀況

ArgumentNullException

source 為 null。

範例

下列範例示範如何實作可用於方法的 Contains 相等比較子。

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，您可以在方法中使用Contains物件序列Product，如下列範例所示：

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

一旦找到相符的專案，列舉就會終止。

如果為 comparernull，則預設相等比較子 Default會用來比較專案與指定的值。

適用於

共用方式為

Enumerable.Contains 方法

定義

多載

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

類型參數

參數

傳回

例外狀況

範例

備註

適用於

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

類型參數

參數

傳回

例外狀況

範例

備註

適用於

其他資源