Enumerable.ElementAtOrDefault(IEnumerable<TSource>, Int32) Enumerable.ElementAtOrDefault(IEnumerable<TSource>, Int32) Enumerable.ElementAtOrDefault(IEnumerable<TSource>, Int32) Enumerable.ElementAtOrDefault(IEnumerable<TSource>, Int32) Method

定義

傳回位於序列中指定索引處的元素;如果索引超出範圍,則傳回預設值。Returns the element at a specified index in a sequence or a default value if the index is out of range.

public:
generic <typename TSource>
[System::Runtime::CompilerServices::Extension]
 static TSource ElementAtOrDefault(System::Collections::Generic::IEnumerable<TSource> ^ source, int index);
public static TSource ElementAtOrDefault<TSource> (this System.Collections.Generic.IEnumerable<TSource> source, int index);
static member ElementAtOrDefault : seq<'Source> * int -> 'Source
<Extension()>
Public Function ElementAtOrDefault(Of TSource) (source As IEnumerable(Of TSource), index As Integer) 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>来傳回的項目。An IEnumerable<T> to return an element from.

index
Int32 Int32 Int32 Int32

要擷取的項目之以零為起始索引。The zero-based index of the element to retrieve.

傳回

TSource TSource TSource TSource

default(TSource) 如果索引超出範圍的來源序列中,否則來源序列中的指定位置處的項目。default(TSource) if the index is outside the bounds of the source sequence; otherwise, the element at the specified position in the source sequence.

例外狀況

範例

下列程式碼範例將示範如何使用 ElementAtOrDefaultThe following code example demonstrates how to use ElementAtOrDefault. 此範例使用陣列界限之外的索引。This example uses an index that is outside the bounds of the array.

string[] names =
    { "Hartono, Tommy", "Adams, Terry", "Andersen, Henriette Thaulow",
        "Hedlund, Magnus", "Ito, Shu" };

int index = 20;

string name = names.ElementAtOrDefault(index);

Console.WriteLine(
    "The name chosen at index {0} is '{1}'.",
    index,
    String.IsNullOrEmpty(name) ? "<no name at this index>" : name);

/*
 This code produces the following output:

 The name chosen at index 20 is '<no name at this index>'.
*/
' Create an array of strings.
Dim names() As String =
{"Hartono, Tommy", "Adams, Terry", "Andersen, Henriette Thaulow", "Hedlund, Magnus", "Ito, Shu"}

Dim index As Integer = 20

' Get a string at an index that is out of range in the array.
Dim name As String = names.ElementAtOrDefault(index)

Dim text As String = If(String.IsNullOrEmpty(name), "[THERE IS NO NAME AT THIS INDEX]", name)

' Display the output.
MsgBox("The name chosen at index " & index & " is " & text)

' This code produces the following output:
'
' The name chosen at index 20 is [THERE IS NO NAME AT THIS INDEX]

備註

如果類型source實作IList<T>,該實作用來取得指定索引處的項目。If the type of source implements IList<T>, that implementation is used to obtain the element at the specified index. 否則,這個方法會取得指定的項目。Otherwise, this method obtains the specified element.

參考和可為 null 類型的預設值是nullThe default value for reference and nullable types is null.

適用於