List<T>.TrimExcess Methode
Definition
Wichtig
Einige Informationen beziehen sich auf Vorabversionen, die vor dem Release ggf. grundlegend überarbeitet werden. Microsoft übernimmt hinsichtlich der hier bereitgestellten Informationen keine Gewährleistungen, seien sie ausdrücklich oder konkludent.
Legt die Kapazität auf die Anzahl der tatsächlich in der List<T> befindlichen Elemente fest, sofern diese Anzahl unter dem Schwellenwert liegt.
public:
void TrimExcess();
public void TrimExcess ();
member this.TrimExcess : unit -> unit
Public Sub TrimExcess ()
Beispiele
Im folgenden Beispiel wird veranschaulicht, wie Sie die Kapazität und Anzahl eines List<T> Objekts überprüfen, das ein einfaches Geschäftsobjekt enthält, und veranschaulicht die Verwendung der TrimExcess Methode zum Entfernen zusätzlicher Kapazität.
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
Das folgende Beispiel veranschaulicht die TrimExcess Methode. Mehrere Eigenschaften und Methoden der List<T> Klasse werden verwendet, um Elemente aus einer Liste von Zeichenfolgen hinzuzufügen, einzufügen und zu entfernen. Anschließend wird die TrimExcess Methode verwendet, um die Kapazität zu verringern, um die Anzahl zu entsprechen, und die Capacity Count Eigenschaften werden angezeigt. Wenn die nicht verwendete Kapazität kleiner als 10 Prozent der Gesamtkapazität war, wäre die Liste nicht geändert worden. Schließlich werden die Inhalte der Liste gelöscht.
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
*)
Hinweise
Diese Methode kann verwendet werden, um den Speicheraufwand einer Auflistung zu minimieren, wenn keine neuen Elemente zur Auflistung hinzugefügt werden. Die Kosten für die Neuverlagerung und das Kopieren eines Großen List<T> können jedoch erheblich sein, sodass die Methode nichts tut, wenn die TrimExcess Liste über 90 Prozent der Kapazität liegt. Dadurch wird vermieden, dass eine große Reallocation-Kosten für einen relativ kleinen Gewinn entstehen.
Hinweis
Der aktuelle Schwellenwert von 90 Prozent kann sich in zukünftigen Versionen ändern.
Diese Methode ist ein O(n)-Vorgang, wobei n ist Count.
Rufen Sie die Methode auf, um den anfangszustand zurückzusetzen List<T> , bevor Sie die Clear TrimExcess Methode aufrufen. Durch das Kürzen eines leeren List<T> Werts wird die Kapazität der List<T> Standardkapazität festgelegt.
Die Kapazität kann auch mithilfe der Capacity Eigenschaft festgelegt werden.