List(Of T).Count Property

Gets the number of elements contained in the List(Of T).

Namespace:  System.Collections.Generic
Assemblies:   mscorlib (in mscorlib.dll)
  System.Collections (in System.Collections.dll)

'Declaration
Public ReadOnly Property Count As Integer

Property Value

Type: System.Int32
The number of elements contained in the List(Of T).

Implements

ICollection(Of T).Count
ICollection.Count
IReadOnlyCollection(Of T).Count

Capacity is the number of elements that the List(Of T) can store before resizing is required. Count is the number of elements that are actually in the List(Of T).

Capacity is always greater than or equal to Count. If Count exceeds Capacity while adding elements, the capacity is increased by automatically reallocating the internal array before copying the old elements and adding the new elements.

Retrieving the value of this property is an O(1) operation.

The following example demonstrates how to check the capacity and count of a List(Of T) that contains a simple business object, and illustrates using the TrimExcess method to remove extra capacity.

Imports System.Collections.Generic
' Simple business object. A PartId is used to identify a part  
' but the part name can change. 
Public Class Part
    Implements IEquatable(Of Part)
    Public Property PartName() As String 
        Get 
            Return m_PartName
        End Get 
        Set(value As String)
            m_PartName = Value
        End Set 
    End Property 
    Private m_PartName As String 
    Public Property PartId() As Integer 
        Get 
            Return m_PartId
        End Get 
        Set(value As Integer)
            m_PartId = Value
        End Set 
    End Property 
    Private m_PartId As Integer 
    Public Overrides Function ToString() As String 
        Return "ID: " & PartId & "   Name: " & PartName
    End Function 
    Public Overrides Function Equals(obj As Object) As Boolean 
        If obj Is Nothing Then 
            Return False 
        End If 
        Dim objAsPart As Part = TryCast(obj, Part)
        If objAsPart Is Nothing Then 
            Return False 
        Else 
            Return Equals(objAsPart)
        End If 
    End Function 
    Public Overrides Function GetHashCode() As Integer 
        Return MyBase.GetHashCode()
    End Function 
    Public Overloads Function Equals(other As Part) As Boolean Implements IEquatable(Of Part).Equals
        If other Is Nothing Then 
            Return False 
        End If 
        Return (Me.PartId.Equals(other.PartId))
    End Function 
    ' Should also override == and != operators. 

End Class 
Public Class Example

    Public Shared Sub Main()
        Dim parts As New List(Of Part)()

        Console.WriteLine(vbLf & "Capacity: {0}", parts.Capacity)

        ' Add parts to the list.
        parts.Add(New Part() With { _
             .PartName = "crank arm", _
             .PartId = 1234 _
        })
        parts.Add(New Part() With { _
             .PartName = "chain ring", _
             .PartId = 1334 _
        })
        parts.Add(New Part() With { _
             .PartName = "regular seat", _
             .PartId = 1434 _
        })
        parts.Add(New Part() With { _
             .PartName = "banana seat", _
             .PartId = 1444 _
        })
        parts.Add(New Part() With { _
             .PartName = "cassette", _
             .PartId = 1534 _
        })
        parts.Add(New Part() With { _
             .PartName = "shift lever", _
             .PartId = 1634 _
        })



        Console.WriteLine()
        For Each aPart As Part In parts
            Console.WriteLine(aPart)
        Next

        Console.WriteLine(vbLf & "Capacity: {0}", parts.Capacity)
        Console.WriteLine("Count: {0}", parts.Count)

        parts.TrimExcess()
        Console.WriteLine(vbLf & "TrimExcess()")
        Console.WriteLine("Capacity: {0}", parts.Capacity)
        Console.WriteLine("Count: {0}", parts.Count)

        parts.Clear()
        Console.WriteLine(vbLf & "Clear()")
        Console.WriteLine("Capacity: {0}", parts.Capacity)
        Console.WriteLine("Count: {0}", parts.Count)
    End Sub 
    
    '     This code example produces the following output.  
    '            Capacity: 0 
    
    '            ID: 1234   Name: crank arm 
    '            ID: 1334   Name: chain ring 
    '            ID: 1434   Name: seat 
    '            ID: 1534   Name: cassette 
    '            ID: 1634   Name: shift lever 
    
    '            Capacity: 8 
    '            Count: 6 
    
    '            TrimExcess() 
    '            Capacity: 6 
    '            Count: 6 
    
    '            Clear() 
    '            Capacity: 6 
    '            Count: 0 
    '      

End Class

The following example shows the value of the Count property at various points in the life of a list. After the list has been created and populated and its elements displayed, the Capacity and Count properties are displayed. These properties are displayed again after the TrimExcess method has been called, and again after the contents of the list are cleared.

Imports System
Imports System.Collections.Generic

Public Class Example

    Public Shared Sub Main()
        Dim dinosaurs As New List(Of String)

        Console.WriteLine(vbLf & "Capacity: {0}", dinosaurs.Capacity)

        dinosaurs.Add("Tyrannosaurus")
        dinosaurs.Add("Amargasaurus")
        dinosaurs.Add("Mamenchisaurus")
        dinosaurs.Add("Deinonychus")
        dinosaurs.Add("Compsognathus")

        Console.WriteLine()
        For Each dinosaur As String In dinosaurs
            Console.WriteLine(dinosaur)
        Next

        Console.WriteLine(vbLf & "Capacity: {0}", dinosaurs.Capacity)
        Console.WriteLine("Count: {0}", dinosaurs.Count)

        Console.WriteLine(vbLf & "Contains(""Deinonychus""): {0}", _
            dinosaurs.Contains("Deinonychus"))

        Console.WriteLine(vbLf & "Insert(2, ""Compsognathus"")")
        dinosaurs.Insert(2, "Compsognathus")

        Console.WriteLine()
        For Each dinosaur As String In dinosaurs
            Console.WriteLine(dinosaur)
        Next 
        ' Shows how to access the list using the Item property.
        Console.WriteLine(vbLf & "dinosaurs(3): {0}", dinosaurs(3))
        Console.WriteLine(vbLf & "Remove(""Compsognathus"")")
        dinosaurs.Remove("Compsognathus")

        Console.WriteLine()
        For Each dinosaur As String In dinosaurs
            Console.WriteLine(dinosaur)
        Next

        dinosaurs.TrimExcess()
        Console.WriteLine(vbLf & "TrimExcess()")
        Console.WriteLine("Capacity: {0}", dinosaurs.Capacity)
        Console.WriteLine("Count: {0}", dinosaurs.Count)

        dinosaurs.Clear()
        Console.WriteLine(vbLf & "Clear()")
        Console.WriteLine("Capacity: {0}", dinosaurs.Capacity)
        Console.WriteLine("Count: {0}", dinosaurs.Count)
    End Sub 
End Class 

' This code example produces the following output: 

'Capacity: 0 

'Tyrannosaurus 
'Amargasaurus 
'Mamenchisaurus 
'Deinonychus 
'Compsognathus 

'Capacity: 8 
'Count: 5 

'Contains("Deinonychus"): True 

'Insert(2, "Compsognathus") 

'Tyrannosaurus 
'Amargasaurus 
'Compsognathus 
'Mamenchisaurus 
'Deinonychus 
'Compsognathus 

'dinosaurs(3): Mamenchisaurus 

'Remove("Compsognathus") 

'Tyrannosaurus 
'Amargasaurus 
'Mamenchisaurus 
'Deinonychus 
'Compsognathus 

'TrimExcess() 
'Capacity: 5 
'Count: 5 

'Clear() 
'Capacity: 5 
'Count: 0

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0, 2.0, 1.0

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Portable Class Library

Supported in: Portable Class Library
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