Enumerable.Single Enumerable.Single Enumerable.Single Enumerable.Single Method

定義

傳回序列的單一特定項目。Returns a single, specific element of a sequence.

多載

Single<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>) Single<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>) Single<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>) Single<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>)

傳回序列中符合指定之條件的唯一一個元素,如果有一個以上這類元素,則擲回例外狀況。Returns the only element of a sequence that satisfies a specified condition, and throws an exception if more than one such element exists.

Single<TSource>(IEnumerable<TSource>) Single<TSource>(IEnumerable<TSource>) Single<TSource>(IEnumerable<TSource>) Single<TSource>(IEnumerable<TSource>)

傳回序列的唯一一個元素,如果序列中不是正好一個元素,則擲回例外狀況。Returns the only element of a sequence, and throws an exception if there is not exactly one element in the sequence.

Single<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>) Single<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>) Single<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>) Single<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>)

傳回序列中符合指定之條件的唯一一個元素,如果有一個以上這類元素,則擲回例外狀況。Returns the only element of a sequence that satisfies a specified condition, and throws an exception if more than one such element exists.

public:
generic <typename TSource>
[System::Runtime::CompilerServices::Extension]
 static TSource Single(System::Collections::Generic::IEnumerable<TSource> ^ source, Func<TSource, bool> ^ predicate);
public static TSource Single<TSource> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,bool> predicate);
static member Single : seq<'Source> * Func<'Source, bool> -> 'Source
<Extension()>
Public Function Single(Of TSource) (source As IEnumerable(Of TSource), predicate As Func(Of TSource, Boolean)) As TSource

類型參數

TSource

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

參數

source
IEnumerable<TSource>

IEnumerable<T>傳回單一項目。An IEnumerable<T> to return a single element from.

predicate
Func<TSource,Boolean>

用來測試項目是否符合條件的函式。A function to test an element for a condition.

傳回

TSource TSource TSource TSource

輸入序列中符合條件的單一項目。The single element of the input sequence that satisfies a condition.

例外狀況

sourcepredicatenullsource or predicate is null.

沒有任何項目符合 predicate 的條件。No element satisfies the condition in predicate.

-或--or- 多個項目符合條件中的predicateMore than one element satisfies the condition in predicate.

-或--or- 來源序列是空的。The source sequence is empty.

範例

下列程式碼範例示範如何使用Single<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>)選取陣列中符合條件的唯一項目。The following code example demonstrates how to use Single<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>) to select the only element of an array that satisfies a condition.

string[] fruits = { "apple", "banana", "mango", 
                      "orange", "passionfruit", "grape" };

string fruit1 = fruits.Single(fruit => fruit.Length > 10);

Console.WriteLine(fruit1);

/*
 This code produces the following output:

 passionfruit
*/
' Create an array of strings.
Dim fruits() As String =
{"apple", "banana", "mango", "orange", "passionfruit", "grape"}

' Get the single item in the array whose length is greater than 10.
Dim result As String =
fruits.Single(Function(fruit) fruit.Length > 10)

' Display the result.
MsgBox("First query: " & result)

下列程式碼範例示範Single<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>)序列不包含只有一個符合條件的項目時,會擲回例外狀況。The following code example demonstrates that Single<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>) throws an exception when the sequence does not contain exactly one element that satisfies the condition.

string fruit2 = null;

try
{
    fruit2 = fruits.Single(fruit => fruit.Length > 15);
}
catch (System.InvalidOperationException)
{
    Console.WriteLine(@"The collection does not contain exactly 
                    one element whose length is greater than 15.");
}

Console.WriteLine(fruit2);

// This code produces the following output:
//
// The collection does not contain exactly  
// one element whose length is greater than 15.
result = String.Empty

' Try to get the single item in the array whose length is > 15.
Try
    result = fruits.Single(Function(fruit) _
                           fruit.Length > 15)
Catch ex As System.InvalidOperationException
    result = "There is not EXACTLY ONE element whose length is > 15."
End Try

' Display the result.
MsgBox("Second query: " & result)

' This code produces the following output:
'
' First query: passionfruit
' Second query: There is not EXACTLY ONE element whose length is > 15.

備註

Single<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>)方法擲回例外狀況,如果輸入的序列不包含任何相符的項目。The Single<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>) method throws an exception if the input sequence contains no matching element. 若要改為傳回null找到任何相符的項目時,使用SingleOrDefaultTo instead return null when no matching element is found, use SingleOrDefault.

Single<TSource>(IEnumerable<TSource>) Single<TSource>(IEnumerable<TSource>) Single<TSource>(IEnumerable<TSource>) Single<TSource>(IEnumerable<TSource>)

傳回序列的唯一一個元素,如果序列中不是正好一個元素,則擲回例外狀況。Returns the only element of a sequence, and throws an exception if there is not exactly one element in the sequence.

public:
generic <typename TSource>
[System::Runtime::CompilerServices::Extension]
 static TSource Single(System::Collections::Generic::IEnumerable<TSource> ^ source);
public static TSource Single<TSource> (this System.Collections.Generic.IEnumerable<TSource> source);
static member Single : seq<'Source> -> 'Source
<Extension()>
Public Function Single(Of TSource) (source As IEnumerable(Of TSource)) As TSource

類型參數

TSource

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

參數

source
IEnumerable<TSource>

IEnumerable<T>来傳回的單一項目。An IEnumerable<T> to return the single element of.

傳回

TSource TSource TSource TSource

輸入序列的單一項目。The single element of the input sequence.

例外狀況

輸入的序列包含一個以上的項目。The input sequence contains more than one element.

-或--or- 輸入的序列是空的。The input sequence is empty.

範例

下列程式碼範例示範如何使用Single<TSource>(IEnumerable<TSource>)選取唯一元素的陣列。The following code example demonstrates how to use Single<TSource>(IEnumerable<TSource>) to select the only element of an array.

string[] fruits1 = { "orange" };

string fruit1 = fruits1.Single();

Console.WriteLine(fruit1);

/*
 This code produces the following output:

 orange
*/
' Create an array that contains one item.
Dim fruits1() As String = {"orange"}

' Get the single item in the array.
Dim result As String = fruits1.Single()

' Display the result.
MsgBox("First query: " & result)

下列程式碼範例示範Single<TSource>(IEnumerable<TSource>)序列不包含只有一個項目時,會擲回例外狀況。The following code example demonstrates that Single<TSource>(IEnumerable<TSource>) throws an exception when the sequence does not contain exactly one element.

string[] fruits2 = { "orange", "apple" };
string fruit2 = null;

try
{
    fruit2 = fruits2.Single();
}
catch (System.InvalidOperationException)
{
    Console.WriteLine("The collection does not contain exactly one element.");
}

Console.WriteLine(fruit2);

/*
 This code produces the following output:

 The collection does not contain exactly one element.
*/
' Create an array that contains two items.
Dim fruits2() As String = {"orange", "apple"}

result = String.Empty

' Try to get the 'single' item in the array.
Try
    result = fruits2.Single()
Catch ex As System.InvalidOperationException
    result = "The collection does not contain exactly one element."
End Try

' Display the result.
MsgBox("Second query: " & result)

' This code produces the following output:
'
' First query: orange
' Second query: The collection does not contain exactly one element.

備註

Single<TSource>(IEnumerable<TSource>)方法擲回例外狀況,如果輸入的序列是空的。The Single<TSource>(IEnumerable<TSource>) method throws an exception if the input sequence is empty. 若要改為傳回null輸入的序列是空的當使用SingleOrDefaultTo instead return null when the input sequence is empty, use SingleOrDefault.

適用於