List<T>.Clear Method

public:
 virtual void Clear();

public void Clear();

abstract member Clear : unit -> unit
override this.Clear : unit -> unit

Public Sub Clear ()

Implements

Examples

The following example demonstrates the Clear method and various other properties and methods of the List<T> generic class. The Clear method is used at the end of the program, to remove all items from the list, and the Capacity and Count properties are then displayed.

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

Partial Public Class Program
 Public Shared Sub ShowPlanets()
 Dim planets As New List(Of String)

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

 planets.Add("Mercury")
 planets.Add("Venus")
 planets.Add("Earth")
 planets.Add("Mars")
 planets.Add("Jupiter")

 Console.WriteLine()
 For Each planet As String In planets
 Console.WriteLine(planet)
 Next

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

 Console.WriteLine(vbLf & "Contains(""Mars""): {0}", _
 planets.Contains("Mars"))

 Console.WriteLine(vbLf & "Insert(2, ""Saturn"")")
 planets.Insert(2, "Saturn")

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

 Console.WriteLine()
 For Each planet As String In planets
 Console.WriteLine(planet)
 Next

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

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

' This code example produces the following output:
'
' Capacity: 0
'
' Mercury
' Venus
' Earth
' Mars
' Jupiter
'
' Capacity: 8
' Count: 5
'
' Contains("Mars"): True
'
' Insert(2, "Saturn")
'
' Mercury
' Venus
' Saturn
' Earth
' Mars
' Jupiter
'
' planets(3): Earth
'
' Remove("Jupiter")
'
' Mercury
' Venus
' Saturn
' Earth
' Mars
'
' 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
 *)

Remarks

Count is set to 0, and references to other objects from elements of the collection are also released.

Capacity remains unchanged. To reset the capacity of the List<T>, call the TrimExcess method or set the Capacity property directly. Decreasing the capacity reallocates memory and copies all the elements in the List<T>. Trimming an empty List<T> sets the capacity of the List<T> to the default capacity.

This method is an O(n) operation, where n is Count.

See also

• TrimExcess()
• Capacity
• Count