Enumerable.Count 方法

定義

命名空間:

System.Linq

組件:

netstandard.dll, System.Linq.dll

傳回序列中的項目數目。

多載

名稱	Description
Count<TSource>(IEnumerable<TSource>)	傳回序列中的項目數目。
Count<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>)	傳回數位，代表指定序列中滿足條件的項目數目。

Count<TSource>(IEnumerable<TSource>)

來源:

Count.cs

傳回序列中的項目數目。

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

元素 source的類型。

參數

source

IEnumerable<TSource>

包含待計數元素的序列。

傳回

Int32

輸入序列中的元素數量。

例外狀況

ArgumentNullException

source 是 null。

OverflowException

其中 source 的元素數量比 Int32.MaxValue 還多。

範例

以下程式碼範例示範如何使用 Count<TSource>(IEnumerable<TSource>) 來計算陣列中的元素。

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

若 的 source 實作類型為 ICollection<T>，則該實作用於取得元素的數量。 否則，此方法決定計數。

當你預期並希望結果大於 LongCount時，使用該MaxValue方法。

在Visual Basic查詢表達式語法中，Aggregate Into Count()子句可轉譯為Count的呼叫。

另請參閱

• 彙總子句 （Visual Basic）

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

來源:

Count.cs

傳回數位，代表指定序列中滿足條件的項目數目。

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

元素 source的類型。

參數

source

IEnumerable<TSource>

一個包含待測試與計數元素的序列。

predicate

Func<TSource,Boolean>

一個用來測試每個元素條件的函數。

傳回

Int32

一個數字，代表序列中有多少元素滿足謂詞函數的條件。

例外狀況

ArgumentNullException

source 或 predicate 為 null。

OverflowException

其中 source 的元素數量比 Int32.MaxValue 還多。

範例

以下程式碼範例示範如何使用 Count<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>) 計算陣列中滿足條件的元素。

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);
        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

若 的 source 實作類型為 ICollection<T>，則該實作用於取得元素的數量。 否則，此方法決定計數。

你應該在預期且希望結果大於 LongCount時使用此MaxValue方法。

在Visual Basic查詢表達式語法中，Aggregate Into Count()子句可轉譯為Count的呼叫。

另請參閱

• 彙總子句 （Visual Basic）