List<T>.TrimExcess Método

Referência

Definição

Namespace:: System.Collections.Generic

Assembly:: System.Collections.dll

Assembly:: mscorlib.dll

Assembly:: netstandard.dll

Origem:: List.cs

Origem:: List.cs

Origem:: List.cs

Importante

Algumas informações se referem a produtos de pré-lançamento que podem ser substancialmente modificados antes do lançamento. A Microsoft não oferece garantias, expressas ou implícitas, das informações aqui fornecidas.

Define a capacidade para o número real de elementos de List<T>, se esse número for menor que um valor limite.

public:
 void TrimExcess();

public void TrimExcess ();

member this.TrimExcess : unit -> unit

Public Sub TrimExcess ()

Exemplos

O exemplo a seguir demonstra como marcar a capacidade e a contagem de um List<T> que contém um objeto comercial simples e ilustra o uso do TrimExcess método para remover a capacidade extra.

using System;
using System.Collections.Generic;
// Simple business object. A PartId is used to identify a part
// but the part name be different for the same Id.
public class Part : IEquatable<Part>
{
    public string PartName { get; set; }
    public int PartId { get; set; }
    public override string ToString()
    {
        return "ID: " + PartId + "   Name: " + PartName;
    }
    public override bool Equals(object obj)
    {
        if (obj == null) return false;
        Part objAsPart = obj as Part;
        if (objAsPart == null) return false;
        else return Equals(objAsPart);
    }
    public override int GetHashCode()
    {
        return base.GetHashCode();
    }
    public bool Equals(Part other)
    {
        if (other == null) return false;
        return (this.PartId.Equals(other.PartId));
    }
    // Should also override == and != operators.
}
public class Example
{

    public static void Main()
    {
        List<Part> parts = new List<Part>();

        Console.WriteLine("\nCapacity: {0}", parts.Capacity);

        parts.Add(new Part() { PartName = "crank arm", PartId = 1234 });
        parts.Add(new Part() { PartName = "chain ring", PartId = 1334 });
        parts.Add(new Part() { PartName = "seat", PartId = 1434 });
        parts.Add(new Part() { PartName = "cassette", PartId = 1534 });
        parts.Add(new Part() { PartName = "shift lever", PartId = 1634 }); ;

        Console.WriteLine();
        foreach (Part aPart in parts)
        {
            Console.WriteLine(aPart);
        }

        Console.WriteLine("\nCapacity: {0}", parts.Capacity);
        Console.WriteLine("Count: {0}", parts.Count);

        parts.TrimExcess();
        Console.WriteLine("\nTrimExcess()");
        Console.WriteLine("Capacity: {0}", parts.Capacity);
        Console.WriteLine("Count: {0}", parts.Count);

        parts.Clear();
        Console.WriteLine("\nClear()");
        Console.WriteLine("Capacity: {0}", parts.Capacity);
        Console.WriteLine("Count: {0}", parts.Count);
    }
    /*
     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: 5

            TrimExcess()
            Capacity: 5
            Count: 5

            Clear()
            Capacity: 5
            Count: 0
     */
}

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

O exemplo a seguir demonstra o TrimExcess método. Várias propriedades e métodos da List<T> classe são usados para adicionar, inserir e remover itens de uma lista de cadeias de caracteres. Em seguida, o TrimExcess método é usado para reduzir a capacidade para corresponder à contagem e as Capacity propriedades e Count são exibidas. Se a capacidade não utilizada tivesse sido inferior a 10% da capacidade total, a lista não teria sido redimensionada. Por fim, o conteúdo da lista é limpo.

using namespace System;
using namespace System::Collections::Generic;

void main()
{
    List<String^>^ dinosaurs = gcnew List<String^>();

    Console::WriteLine("\nCapacity: {0}", dinosaurs->Capacity);

    dinosaurs->Add("Tyrannosaurus");
    dinosaurs->Add("Amargasaurus");
    dinosaurs->Add("Mamenchisaurus");
    dinosaurs->Add("Deinonychus");
    dinosaurs->Add("Compsognathus");

    Console::WriteLine();
    for each(String^ dinosaur in dinosaurs )
    {
        Console::WriteLine(dinosaur);
    }

    Console::WriteLine("\nCapacity: {0}", dinosaurs->Capacity);
    Console::WriteLine("Count: {0}", dinosaurs->Count);

    Console::WriteLine("\nContains(\"Deinonychus\"): {0}",
        dinosaurs->Contains("Deinonychus"));

    Console::WriteLine("\nInsert(2, \"Compsognathus\")");
    dinosaurs->Insert(2, "Compsognathus");

    Console::WriteLine();
    for each(String^ dinosaur in dinosaurs )
    {
        Console::WriteLine(dinosaur);
    }

    Console::WriteLine("\ndinosaurs[3]: {0}", dinosaurs[3]);

    Console::WriteLine("\nRemove(\"Compsognathus\")");
    dinosaurs->Remove("Compsognathus");

    Console::WriteLine();
    for each(String^ dinosaur in dinosaurs )
    {
        Console::WriteLine(dinosaur);
    }

    dinosaurs->TrimExcess();
    Console::WriteLine("\nTrimExcess()");
    Console::WriteLine("Capacity: {0}", dinosaurs->Capacity);
    Console::WriteLine("Count: {0}", dinosaurs->Count);

    dinosaurs->Clear();
    Console::WriteLine("\nClear()");
    Console::WriteLine("Capacity: {0}", dinosaurs->Capacity);
    Console::WriteLine("Count: {0}", dinosaurs->Count);
}

/* 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
 */

List<string> dinosaurs = new List<string>();

Console.WriteLine("\nCapacity: {0}", dinosaurs.Capacity);

dinosaurs.Add("Tyrannosaurus");
dinosaurs.Add("Amargasaurus");
dinosaurs.Add("Mamenchisaurus");
dinosaurs.Add("Deinonychus");
dinosaurs.Add("Compsognathus");
Console.WriteLine();
foreach(string dinosaur in dinosaurs)
{
    Console.WriteLine(dinosaur);
}

Console.WriteLine("\nCapacity: {0}", dinosaurs.Capacity);
Console.WriteLine("Count: {0}", dinosaurs.Count);

Console.WriteLine("\nContains(\"Deinonychus\"): {0}",
    dinosaurs.Contains("Deinonychus"));

Console.WriteLine("\nInsert(2, \"Compsognathus\")");
dinosaurs.Insert(2, "Compsognathus");

Console.WriteLine();
foreach(string dinosaur in dinosaurs)
{
    Console.WriteLine(dinosaur);
}

// Shows accessing the list using the Item property.
Console.WriteLine("\ndinosaurs[3]: {0}", dinosaurs[3]);

Console.WriteLine("\nRemove(\"Compsognathus\")");
dinosaurs.Remove("Compsognathus");

Console.WriteLine();
foreach(string dinosaur in dinosaurs)
{
    Console.WriteLine(dinosaur);
}

dinosaurs.TrimExcess();
Console.WriteLine("\nTrimExcess()");
Console.WriteLine("Capacity: {0}", dinosaurs.Capacity);
Console.WriteLine("Count: {0}", dinosaurs.Count);

dinosaurs.Clear();
Console.WriteLine("\nClear()");
Console.WriteLine("Capacity: {0}", dinosaurs.Capacity);
Console.WriteLine("Count: {0}", dinosaurs.Count);

/* 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
 */

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


[<EntryPoint>]
let main argv = 
    // We refer to System.Collections.Generic.List<'T> by its type 
    // abbreviation ResizeArray<'T> to avoid conflict with the List module.    
    // Note: In F# code, F# linked lists are usually preferred over
    // ResizeArray<'T> when an extendable collection is required.
    let dinosaurs = ResizeArray<_>()
 
    // Write out the dinosaurs in the ResizeArray.
    let printDinosaurs() =
        printfn ""
        dinosaurs |> Seq.iter (fun p -> printfn "%O" p) 
 
    
    printfn "\nCapacity: %i" dinosaurs.Capacity
 
    dinosaurs.Add("Tyrannosaurus")
    dinosaurs.Add("Amargasaurus")
    dinosaurs.Add("Mamenchisaurus")
    dinosaurs.Add("Deinonychus")
    dinosaurs.Add("Compsognathus")
 
    printDinosaurs()
 
    printfn "\nCapacity: %i" dinosaurs.Capacity
    printfn "Count: %i" dinosaurs.Count
 
    printfn "\nContains(\"Deinonychus\"): %b" (dinosaurs.Contains("Deinonychus"))
 
    printfn "\nInsert(2, \"Compsognathus\")"
    dinosaurs.Insert(2, "Compsognathus")
 
    printDinosaurs()
 
    // Shows accessing the list using the Item property.
    printfn "\ndinosaurs[3]: %s" dinosaurs.[3]
 
    printfn "\nRemove(\"Compsognathus\")"
    dinosaurs.Remove("Compsognathus") |> ignore
 
    printDinosaurs()
 
    dinosaurs.TrimExcess()
    printfn "\nTrimExcess()"
    printfn "Capacity: %i" dinosaurs.Capacity
    printfn "Count: %i" dinosaurs.Count
 
    dinosaurs.Clear()
    printfn "\nClear()"
    printfn "Capacity: %i" dinosaurs.Capacity
    printfn "Count: %i" dinosaurs.Count
 
    0 // return an integer exit code
 
    (* 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
    *)

Comentários

Esse método pode ser usado para minimizar a sobrecarga de memória de uma coleção se nenhum elemento novo for adicionado à coleção. No entanto, o custo de realocar e copiar um grande List<T> pode ser considerável, portanto, o TrimExcess método não fará nada se a lista estiver em mais de 90% da capacidade. Isso evita incorrer em um grande custo de realocação para um ganho relativamente pequeno.

Observação

O limite atual de 90% pode mudar em versões futuras.

Esse método é uma operação O(n), em que n é Count.

Para redefinir um List<T> para seu estado inicial, chame o Clear método antes de chamar o TrimExcess método . Cortar um vazio List<T> define a capacidade do List<T> como a capacidade padrão.

A capacidade também pode ser definida usando a Capacity propriedade .

Aplica-se a

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List<T>.TrimExcess Método

Definição

Exemplos

Comentários

Aplica-se a

Confira também

Recursos adicionais