Enumerable.Contains Metodo
Definizione
Determina se una sequenza contiene un elemento specifico.Determines whether a sequence contains a specified element.
Overload
Contains<TSource>(IEnumerable<TSource>, TSource) |
Determina se una sequenza contiene uno specifico elemento utilizzando l'operatore di confronto uguaglianze predefinito.Determines whether a sequence contains a specified element by using the default equality comparer. |
Contains<TSource>(IEnumerable<TSource>, TSource, IEqualityComparer<TSource>) |
Determina se una sequenza contiene un elemento specificato utilizzando un oggetto IEqualityComparer<T> specificato.Determines whether a sequence contains a specified element by using a specified IEqualityComparer<T>. |
Contains<TSource>(IEnumerable<TSource>, TSource)
Determina se una sequenza contiene uno specifico elemento utilizzando l'operatore di confronto uguaglianze predefinito.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
Parametri di tipo
- TSource
Tipo degli elementi di source
.The type of the elements of source
.
Parametri
- source
- IEnumerable<TSource>
Sequenza in cui individuare un valore.A sequence in which to locate a value.
- value
- TSource
Valore da individuare nella sequenza .The value to locate in the sequence.
Restituisce
true
se la sequenza di origine contiene un elemento con il valore specificato; altrimenti, false
.true
if the source sequence contains an element that has the specified value; otherwise, false
.
Eccezioni
source
è null
.source
is null
.
Esempio
Nell'esempio di codice riportato di seguito viene illustrato come utilizzare Contains<TSource>(IEnumerable<TSource>, TSource) per determinare se una matrice contiene un elemento specifico.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
Commenti
Se il tipo di source
implementa ICollection<T> , Contains
viene richiamato il metodo in tale implementazione per ottenere il risultato.If the type of source
implements ICollection<T>, the Contains
method in that implementation is invoked to obtain the result. In caso contrario, questo metodo determina se source
contiene l'elemento specificato.Otherwise, this method determines whether source
contains the specified element.
L'enumerazione viene terminata non appena viene trovato un elemento corrispondente.Enumeration is terminated as soon as a matching element is found.
Gli elementi vengono confrontati con il valore specificato utilizzando l'operatore di confronto di uguaglianza predefinito Default .Elements are compared to the specified value by using the default equality comparer, Default.
Si applica a
Contains<TSource>(IEnumerable<TSource>, TSource, IEqualityComparer<TSource>)
Determina se una sequenza contiene un elemento specificato utilizzando un oggetto IEqualityComparer<T> specificato.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
Parametri di tipo
- TSource
Tipo degli elementi di source
.The type of the elements of source
.
Parametri
- source
- IEnumerable<TSource>
Sequenza in cui individuare un valore.A sequence in which to locate a value.
- value
- TSource
Valore da individuare nella sequenza .The value to locate in the sequence.
- comparer
- IEqualityComparer<TSource>
Operatore di confronto uguaglianze per confrontare valori.An equality comparer to compare values.
Restituisce
true
se la sequenza di origine contiene un elemento con il valore specificato; altrimenti, false
.true
if the source sequence contains an element that has the specified value; otherwise, false
.
Eccezioni
source
è null
.source
is null
.
Esempio
Nell'esempio seguente viene illustrato come implementare un operatore di confronto di uguaglianza che può essere utilizzato nel Contains metodo.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
Dopo aver implementato questo operatore di confronto, è possibile usare una sequenza di Product
oggetti nel Contains metodo, come illustrato nell'esempio seguente: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
Commenti
L'enumerazione viene terminata non appena viene trovato un elemento corrispondente.Enumeration is terminated as soon as a matching element is found.
Se comparer
è null
, viene usato l'operatore di confronto di uguaglianza predefinito, Default , per confrontare gli elementi con il valore specificato.If comparer
is null
, the default equality comparer, Default, is used to compare elements to the specified value.