List<T>.Clear Metodo

Definizione

Spazio dei nomi:

System.Collections.Generic

Assembly:

netstandard.dll, System.Collections.dll

Origine:

List.cs

Rimuove tutti gli elementi da List<T>.

public:
 virtual void Clear();

public void Clear();

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

Public Sub Clear ()

Implementazioni

Clear() Clear()

Esempio

Nell'esempio seguente viene illustrato il Clear metodo e varie altre proprietà e metodi della List<T> classe generica. Il Clear metodo viene utilizzato alla fine del programma, per rimuovere tutti gli elementi dall'elenco e le Capacity proprietà e Count vengono quindi visualizzate.

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
    *)

Commenti

Count è impostato su 0 e vengono rilasciati anche riferimenti ad altri oggetti degli elementi della raccolta.

Capacity rimane invariato. Per reimpostare la capacità di List<T>, chiamare il TrimExcess metodo o impostare direttamente la Capacity proprietà . La riduzione della capacità rialloca la memoria e copia tutti gli elementi in List<T>. Il taglio di un oggetto vuoto List<T> imposta la capacità dell'oggetto List<T> sulla capacità predefinita.

Questo metodo è un'operazione O(n), dove n è Count.

Vedi anche

• TrimExcess()
• Capacity
• Count