Enumerable.Count 方法

定義

傳回序列中的項目數。Returns the number of elements in a sequence.

多載

Count<TSource>(IEnumerable<TSource>)

傳回序列中的項目數。Returns the number of elements in a sequence.

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

傳回數字,代表指定之序列中符合條件的項目數目。Returns a number that represents how many elements in the specified sequence satisfy a condition.

Count<TSource>(IEnumerable<TSource>)

傳回序列中的項目數。Returns the number of elements in a sequence.

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

類型參數

TSource

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

參數

source
IEnumerable<TSource>

包含要計算之項目的序列。A sequence that contains elements to be counted.

傳回

Int32

輸入序列中的項目數目。The number of elements in the input sequence.

例外狀況

sourcenullsource is null.

source 中的項目數目大於 MaxValueThe number of elements in source is larger than MaxValue.

範例

下列程式碼範例示範如何使用 Count<TSource>(IEnumerable<TSource>) 來計算陣列中的元素。The following code example demonstrates how to use Count<TSource>(IEnumerable<TSource>) to count the elements in an array.

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

try
{
    int numberOfFruits = fruits.Count();
    Console.WriteLine(
        "There are {0} fruits in the collection.",
        numberOfFruits);
}
catch (OverflowException)
{
    Console.WriteLine("The count is too large to store as an Int32.");
    Console.WriteLine("Try using the LongCount() method instead.");
}

// This code produces the following output:
//
// There are 6 fruits in the collection.
' Create an array of strings.
Dim fruits() As String = {"apple", "banana", "mango", "orange", "passionfruit", "grape"}

Try
    ' Count the number of items in the array.
    Dim numberOfFruits As Integer = fruits.Count()
    ' Display the output.
    Console.WriteLine($"There are {numberOfFruits} fruits in the collection.")
Catch e As OverflowException
    Console.WriteLine("The count is too large to store as an Int32. Try using LongCount() instead.")
End Try

' This code produces the following output:
'
' There are 6 fruits in the collection.

備註

如果實作為型 sourceICollection<T> ,則會使用該執行來取得專案的計數。If the type of source implements ICollection<T>, that implementation is used to obtain the count of elements. 否則,此方法會決定計數。Otherwise, this method determines the count.

LongCount當您預期並想要讓結果大於時,請使用方法 MaxValueUse the LongCount method when you expect and want to allow the result to be greater than MaxValue.

在 Visual Basic 查詢運算式語法中, Aggregate Into Count() 子句會轉譯為的調用 CountIn Visual Basic query expression syntax, an Aggregate Into Count() clause translates to an invocation of Count.

另請參閱

適用於

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

傳回數字,代表指定之序列中符合條件的項目數目。Returns a number that represents how many elements in the specified sequence satisfy a condition.

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

類型參數

TSource

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

參數

source
IEnumerable<TSource>

包含要測試及計算之項目的序列。A sequence that contains elements to be tested and counted.

predicate
Func<TSource,Boolean>

用來測試每個項目是否符合條件的函式。A function to test each element for a condition.

傳回

Int32

數字,代表序列中符合述詞函式之條件的項目數目。A number that represents how many elements in the sequence satisfy the condition in the predicate function.

例外狀況

sourcepredicatenullsource or predicate is null.

source 中的項目數目大於 MaxValueThe number of elements in source is larger than MaxValue.

範例

下列程式碼範例示範如何使用 Count<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>) 來計算陣列中滿足條件的元素。The following code example demonstrates how to use Count<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>) to count the elements in an array that satisfy a condition.

class Pet
{
    public string Name { get; set; }
    public bool Vaccinated { get; set; }
}

public static void CountEx2()
{
    Pet[] pets = { new Pet { Name="Barley", Vaccinated=true },
                   new Pet { Name="Boots", Vaccinated=false },
                   new Pet { Name="Whiskers", Vaccinated=false } };

    try
    {
        int numberUnvaccinated = pets.Count(p => p.Vaccinated == false);
        Console.WriteLine("There are {0} unvaccinated animals.", numberUnvaccinated);
    }
    catch (OverflowException)
    {
        Console.WriteLine("The count is too large to store as an Int32.");
        Console.WriteLine("Try using the LongCount() method instead.");
    }
}

// This code produces the following output:
//
// There are 2 unvaccinated animals.
Structure Pet
    Public Name As String
    Public Vaccinated As Boolean
End Structure

Public Shared Sub CountEx2()
    ' Create an array of Pet objects.
    Dim pets() As Pet = {New Pet With {.Name = "Barley", .Vaccinated = True},
                 New Pet With {.Name = "Boots", .Vaccinated = False},
                 New Pet With {.Name = "Whiskers", .Vaccinated = False}}

    Try
        ' Count the number of Pets in the array where the Vaccinated property is False.
        Dim numberUnvaccinated As Integer =
    pets.Count(Function(p) p.Vaccinated = False)
        ' Display the output.
        Console.WriteLine($"There are {numberUnvaccinated} unvaccinated animals.")
    Catch e As OverflowException
        Console.WriteLine("The count is too large to store as an Int32. Try using LongCount() instead.")
    End Try

End Sub

' This code produces the following output:
'
' There are 2 unvaccinated animals.

備註

如果實作為型 sourceICollection<T> ,則會使用該執行來取得專案的計數。If the type of source implements ICollection<T>, that implementation is used to obtain the count of elements. 否則,此方法會決定計數。Otherwise, this method determines the count.

您應該在 LongCount 預期的情況使用方法,並想要讓結果大於 MaxValueYou should use the LongCount method when you expect and want to allow the result to be greater than MaxValue.

在 Visual Basic 查詢運算式語法中, Aggregate Into Count() 子句會轉譯為的調用 CountIn Visual Basic query expression syntax, an Aggregate Into Count() clause translates to an invocation of Count.

另請參閱

適用於