Enumerable.Contains 方法
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) |
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。Determines whether a sequence contains a specified element by using the default equality comparer. |
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。Determines whether a sequence contains a specified element by using a specified IEqualityComparer<T>. |
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。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
要在序列中尋找的值。The value to locate in the sequence.
傳回
如果來源序列包含具有指定值的項目,則為 true
,否則為 false
。true
if the source sequence contains an element that has the specified value; otherwise, false
.
例外狀況
source
為 null
。source
is null
.
範例
下列程式碼範例將示範如何使用 Contains<TSource>(IEnumerable<TSource>, TSource) 來判斷陣列是否包含特定的元素。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
備註
如果實作為型 source
別 ICollection<T> ,則 Contains
會叫用該實作為的方法來取得結果。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
包含指定的元素。Otherwise, this method determines whether source
contains the specified element.
一旦找到相符的元素,就會終止列舉。Enumeration is terminated as soon as a matching element is found.
使用預設相等比較子來比較元素與指定的值 Default 。Elements are compared to the specified value by using the default equality comparer, Default.
適用於
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。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);
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
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
如果來源序列包含具有指定值的項目,則為 true
,否則為 false
。true
if the source sequence contains an element that has the specified value; otherwise, false
.
例外狀況
source
為 null
。source
is null
.
範例
下列範例示範如何執行可用於方法的相等比較子 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
在您執行此比較子之後,您可以 Product
在方法中使用一連串的物件 Contains ,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
一旦找到相符的元素,就會終止列舉。Enumeration is terminated as soon as a matching element is found.
如果 comparer
為 null
,則會使用預設的相等比較子來 Default 比較元素與指定的值。If comparer
is null
, the default equality comparer, Default, is used to compare elements to the specified value.