Sets the capacity to the actual number of elements in the ListT, if that number is less than a threshold value.
Assembly: mscorlib (in mscorlib.dll)
This method can be used to minimize a collection's memory overhead if no new elements will be added to the collection. The cost of reallocating and copying a large ListT can be considerable, however, so the TrimExcess method does nothing if the list is at more than 90 percent of capacity. This avoids incurring a large reallocation cost for a relatively small gain.
.gif) Note |
|---|
The current threshold of 90 percent might change in future releases. |
This method is an O(n) operation, where n is Count.
To reset a ListT to its initial state, call the Clear method before calling the TrimExcess method. Trimming an empty ListT sets the capacity of the ListT to the default capacity.
The capacity can also be set using the Capacity property.
The following code example demonstrates the TrimExcess method. Several properties and methods of the ListT class are used to add, insert, and remove items from a list of strings. Then the TrimExcess method is used to reduce the capacity to match the count, and the Capacity and Count properties are displayed. If the unused capacity had been less than 10 percent of total capacity, the list would not have been resized. Finally, 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
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: 0using System;
using System.Collections.Generic;
public class Example
{
public static void Main()
{
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);
}
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
*/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
*/Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
