Enumerable.Single 方法
重要
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返回序列中的单个特定元素。
| Single<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>) |
返回序列中满足指定条件的唯一元素；如果有多个这样的元素存在，则会引发异常。 |
| Single<TSource>(IEnumerable<TSource>) |
返回序列的唯一元素；如果该序列并非恰好包含一个元素，则会引发异常。 |
- Source:
- Single.cs
- Source:
- Single.cs
- Source:
- Single.cs
返回序列中满足指定条件的唯一元素；如果有多个这样的元素存在，则会引发异常。
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类型参数
- TSource
source 的元素类型。
参数
- source
- IEnumerable<TSource>
要从中返回单个元素的 IEnumerable<T>。
返回
TSource
输入序列中满足条件的单个元素。
例外
source 或 predicate 为 null。
示例
下面的代码示例演示如何使用 Single<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>) 选择满足条件的数组中唯一的元素。
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.
Console.WriteLine($"First query: {result}")
下面的代码示例演示当 Single<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>) 序列不包含满足条件的元素时引发异常。
string fruit2 = null;
try
{
fruit2 = fruits.Single(fruit => fruit.Length > 15);
}
catch (System.InvalidOperationException)
{
Console.WriteLine(@"The collection does not contain exactly
one element whose length is greater than 15.");
}
Console.WriteLine(fruit2);
// This code produces the following output:
//
// The collection does not contain exactly
// one element whose length is greater than 15.
result = String.Empty
' Try to get the single item in the array whose length is > 15.
Try
result = fruits.Single(Function(fruit) _
fruit.Length > 15)
Catch ex As System.InvalidOperationException
result = "There is not EXACTLY ONE element whose length is > 15."
End Try
' Display the result.
Console.WriteLine($"Second query: {result}")
' This code produces the following output:
'
' First query: passionfruit
' Second query: There is not EXACTLY ONE element whose length is > 15.
注解
如果输入序列不包含匹配元素，则 Single<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>) 方法将引发异常。 若要在找不到匹配元素时返回 null ，请使用 SingleOrDefault。
适用于
.NET 9 和其他版本
| 产品 | 版本 |
|---|---|
| .NET | Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9 |
| .NET Framework | 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1 |
| .NET Standard | 1.0, 1.1, 1.2, 1.3, 1.4, 1.6, 2.0, 2.1 |
| UWP | 10.0 |
- Source:
- Single.cs
- Source:
- Single.cs
- Source:
- Single.cs
返回序列的唯一元素；如果该序列并非恰好包含一个元素，则会引发异常。
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类型参数
- TSource
source 的元素类型。
参数
- source
- IEnumerable<TSource>
要返回其单个元素的 IEnumerable<T>。
返回
TSource
输入序列的单个元素。
例外
source 为 null。
示例
下面的代码示例演示如何使用 Single<TSource>(IEnumerable<TSource>) 选择数组的唯一元素。
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.
Console.WriteLine($"First query: {result}")
下面的代码示例演示当 Single<TSource>(IEnumerable<TSource>) 序列不包含正好包含一个元素时引发异常的 。
string[] fruits2 = { "orange", "apple" };
string fruit2 = null;
try
{
fruit2 = fruits2.Single();
}
catch (System.InvalidOperationException)
{
Console.WriteLine("The collection does not contain exactly one element.");
}
Console.WriteLine(fruit2);
/*
This code produces the following output:
The collection does not contain exactly one element.
*/
' Create an array that contains two items.
Dim fruits2() As String = {"orange", "apple"}
result = String.Empty
' Try to get the 'single' item in the array.
Try
result = fruits2.Single()
Catch ex As System.InvalidOperationException
result = "The collection does not contain exactly one element."
End Try
' Display the result.
Console.WriteLine($"Second query: {result}")
' This code produces the following output:
'
' First query: orange
' Second query: The collection does not contain exactly one element.
注解
如果输入序列为空，方法 Single<TSource>(IEnumerable<TSource>) 将引发异常。 若要在输入序列为空时返回 null ，请使用 SingleOrDefault。
适用于
.NET 9 和其他版本
| 产品 | 版本 |
|---|---|
| .NET | Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9 |
| .NET Framework | 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1 |
| .NET Standard | 1.0, 1.1, 1.2, 1.3, 1.4, 1.6, 2.0, 2.1 |
| UWP | 10.0 |
