System.Collections.Generic.List<T> 類別

發行項
04/04/2025

本文提供此 API 參考文件的補充備註。

類別 List<T> 是類別 ArrayList 的泛型等價類別。它使用一個能夠根據需要動態增加大小的陣列來實現IList<T>泛型介面。

您可以使用 Add 或 AddRange 方法，將專案新增至 List<T>。

類別 List<T> 同時使用相等比較子和排序比較子。

方法如Contains、IndexOf、LastIndexOf和Remove會針對清單元素使用相等比對器。類型 T 的預設相等比較子會依下列方式決定。如果類型 T 實作 IEquatable<T> 泛型介面，則相等比較子是 Equals(T) 該介面的方法，否則，默認相等比較子為 Object.Equals(Object)。
像BinarySearch和Sort這類方法會針對清單專案使用排序比較子。類型 T 的預設比較子會依下列方式決定。如果類型 T 實作 IComparable<T> 泛型介面，則預設比較子是 CompareTo(T) 該介面的方法;否則，如果類型 T 實作非泛型 IComparable 介面，則預設比較子就是 CompareTo(Object) 該介面的方法。如果類型 T 未實作這兩個介面，則沒有預設比較子，而且必須明確提供比較子或比較委派。

List<T>不保證會排序。您必須先排序 List<T> ，才能執行需要List<T>排序的作業（例如BinarySearch）。

這個集合中的元素可以使用整數索引來存取。此集合中的索引是以零起始。

僅限 .NET Framework：對於非常大的List<T>物件，您可以在運行時環境中將組態元素<gcAllowVeryLargeObjects>的enabled屬性設定為true，以將64位系統上的最大容量增加到20億個元素。

List<T> 接受 null 作為參考類型的有效值，並允許重複元素。

如需類別的 List<T> 不可變版本，請參閱 ImmutableList<T>。

效能考量

在決定是否要使用 List<T> 或 ArrayList 類別時，兩者都有類似的功能，請記住，在大部分情況下，類別 List<T> 的執行效果更好，而且類型安全。如果在某個T類別中使用引用類型List<T>，則這兩個類別的行為是相同的。不過，如果是在型別 T 使用實值型別，您必須考慮實作和封箱問題。

如果實值型別用於型 T別，編譯程式就會針對該實值型別產生類別的 List<T> 實作。這表示物件的清單專案 List<T> 不需要在可以使用專案之前進行 Boxed，而且在建立大約 500 個清單元素之後，未將清單專案儲存的記憶體大於用來產生類別實作的記憶體。

請確定用於類型 T 的值類型實作了泛型介面 IEquatable<T>。如果沒有，這類 Contains 方法必須呼叫 Object.Equals(Object) 方法，以將受影響的清單元素裝箱。如果實值型別實作了 IComparable 介面且您擁有其原始程式碼，應同時實作 IComparable<T> 泛型介面，以防止 BinarySearch 和 Sort 方法對清單項目進行裝箱。如果您沒有原始程式碼，請將對象傳遞 IComparer<T> 至 BinarySearch 和 Sort 方法。

為了獲得優勢，建議使用List<T>類別的特定類型實作，而不是使用ArrayList類別或自行撰寫強型別包裝集合。這是因為您的實作必須為您執行 .NET 的功能，而且 .NET 運行時間可以共用通用中繼語言程式代碼和元數據，而您的實作則無法這麼做。

F# 考量因素

類別 List<T> 在 F# 程式代碼中不常使用。相反清單，是不可變的單向鏈結清單，通常更被偏好。 F# List 提供已排序且不可變的數列值，而且支援在功能樣式開發中使用。從 F# 使用時， List<T> 類別通常會由 ResizeArray<'T> 類型縮寫參照，以避免與 F# 清單發生命名衝突。

範例

下列範例示範如何在中 List<T>新增、移除和插入簡單的商業物件。

using System;
using System.Collections.Generic;

// Simple business object. A PartId is used to identify the type of part
// but the part name can change.
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 PartId;
    }
    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()
    {
        // Create a list of parts.
        List<Part> parts =
        [
            // Add parts to the list.
            new Part() { PartName = "crank arm", PartId = 1234 },
            new Part() { PartName = "chain ring", PartId = 1334 },
            new Part() { PartName = "regular seat", PartId = 1434 },
            new Part() { PartName = "banana seat", PartId = 1444 },
            new Part() { PartName = "cassette", PartId = 1534 },
            new Part() { PartName = "shift lever", PartId = 1634 },
        ];

        // Write out the parts in the list. This will call the overridden ToString method
        // in the Part class.
        Console.WriteLine();
        foreach (Part aPart in parts)
        {
            Console.WriteLine(aPart);
        }

        // Check the list for part #1734. This calls the IEquatable.Equals method
        // of the Part class, which checks the PartId for equality.
        Console.WriteLine($"""
        Contains("1734"): {parts.Contains(new Part { PartId = 1734, PartName = "" })}
        """);

        // Insert a new item at position 2.
        Console.WriteLine("\nInsert(2, \"1834\")");
        parts.Insert(2, new Part() { PartName = "brake lever", PartId = 1834 });

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

        Console.WriteLine($"\nParts[3]: {parts[3]}");

        Console.WriteLine("\nRemove(\"1534\")");

        // This will remove part 1534 even though the PartName is different,
        // because the Equals method only checks PartId for equality.
        parts.Remove(new Part() { PartId = 1534, PartName = "cogs" });

        Console.WriteLine();
        foreach (Part aPart in parts)
        {
            Console.WriteLine(aPart);
        }
        Console.WriteLine("\nRemoveAt(3)");
        // This will remove the part at index 3.
        parts.RemoveAt(3);

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

        /*

         ID: 1234   Name: crank arm
         ID: 1334   Name: chain ring
         ID: 1434   Name: regular seat
         ID: 1444   Name: banana seat
         ID: 1534   Name: cassette
         ID: 1634   Name: shift lever

         Contains("1734"): False

         Insert(2, "1834")
         ID: 1234   Name: crank arm
         ID: 1334   Name: chain ring
         ID: 1834   Name: brake lever
         ID: 1434   Name: regular seat
         ID: 1444   Name: banana seat
         ID: 1534   Name: cassette
         ID: 1634   Name: shift lever

         Parts[3]: ID: 1434   Name: regular seat

         Remove("1534")

         ID: 1234   Name: crank arm
         ID: 1334   Name: chain ring
         ID: 1834   Name: brake lever
         ID: 1434   Name: regular seat
         ID: 1444   Name: banana seat
         ID: 1634   Name: shift lever

         RemoveAt(3)

         ID: 1234   Name: crank arm
         ID: 1334   Name: chain ring
         ID: 1834   Name: brake lever
         ID: 1444   Name: banana seat
         ID: 1634   Name: shift lever


     */
    }
}


' Simple business object. A PartId is used to identify the type of 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 PartId
    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()
        ' Create a list of parts.
        Dim parts As New List(Of Part)()

        ' 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
        })



        ' Write out the parts in the list. This will call the overridden ToString method
        ' in the Part class.
        Console.WriteLine()
        For Each aPart As Part In parts
            Console.WriteLine(aPart)
        Next


        ' Check the list for part #1734. This calls the IEquatable.Equals method
        ' of the Part class, which checks the PartId for equality.
        Console.WriteLine(vbLf & "Contains(""1734""): {0}", parts.Contains(New Part() With {
             .PartId = 1734,
             .PartName = ""
        }))

        ' Insert a new item at position 2.
        Console.WriteLine(vbLf & "Insert(2, ""1834"")")
        parts.Insert(2, New Part() With {
             .PartName = "brake lever",
             .PartId = 1834
        })


        'Console.WriteLine();
        For Each aPart As Part In parts
            Console.WriteLine(aPart)
        Next

        Console.WriteLine(vbLf & "Parts[3]: {0}", parts(3))

        Console.WriteLine(vbLf & "Remove(""1534"")")

        ' This will remove part 1534 even though the PartName is different,
        ' because the Equals method only checks PartId for equality.
        parts.Remove(New Part() With {
             .PartId = 1534,
             .PartName = "cogs"
        })

        Console.WriteLine()
        For Each aPart As Part In parts
            Console.WriteLine(aPart)
        Next

        Console.WriteLine(vbLf & "RemoveAt(3)")
        ' This will remove part at index 3.
        parts.RemoveAt(3)

        Console.WriteLine()
        For Each aPart As Part In parts
            Console.WriteLine(aPart)
        Next
    End Sub
    '
    '        This example code produces the following output:
    '        ID: 1234   Name: crank arm
    '        ID: 1334   Name: chain ring
    '        ID: 1434   Name: regular seat
    '        ID: 1444   Name: banana seat
    '        ID: 1534   Name: cassette
    '        ID: 1634   Name: shift lever
    '
    '        Contains("1734"): False
    '
    '        Insert(2, "1834")
    '        ID: 1234   Name: crank arm
    '        ID: 1334   Name: chain ring
    '        ID: 1834   Name: brake lever
    '        ID: 1434   Name: regular seat
    '        ID: 1444   Name: banana seat
    '        ID: 1534   Name: cassette
    '        ID: 1634   Name: shift lever
    '
    '        Parts[3]: ID: 1434   Name: regular seat
    '
    '        Remove("1534")
    '
    '        ID: 1234   Name: crank arm
    '        ID: 1334   Name: chain ring
    '        ID: 1834   Name: brake lever
    '        ID: 1434   Name: regular seat
    '        ID: 1444   Name: banana seat
    '        ID: 1634   Name: shift lever
    '   '
    '        RemoveAt(3)
    '
    '        ID: 1234   Name: crank arm
    '        ID: 1334   Name: chain ring
    '        ID: 1834   Name: brake lever
    '        ID: 1444   Name: banana seat
    '        ID: 1634   Name: shift lever
    '        

End Class


// Simple business object. A PartId is used to identify the type of part  
// but the part name can change.  
[<CustomEquality; NoComparison>]
type Part = { PartId : int ; mutable PartName : string } with
    override this.GetHashCode() = hash this.PartId
    override this.Equals(other) =
        match other with
        | :? Part as p -> this.PartId = p.PartId
        | _ -> false
    override this.ToString() = sprintf "ID: %i   Name: %s" this.PartId this.PartName

[<EntryPoint>]
let main argv = 
    // We refer to System.Collections.Generic.List<'T> by its type 
    // abbreviation ResizeArray<'T> to avoid conflicts with the F# List module.    
    // Note: In F# code, F# linked lists are usually preferred over
    // ResizeArray<'T> when an extendable collection is required.
    let parts = ResizeArray<_>()
    parts.Add({PartName = "crank arm" ; PartId = 1234})
    parts.Add({PartName = "chain ring"; PartId = 1334 })
    parts.Add({PartName = "regular seat"; PartId = 1434 })
    parts.Add({PartName = "banana seat"; PartId = 1444 })
    parts.Add({PartName = "cassette"; PartId = 1534 })
    parts.Add({PartName = "shift lever"; PartId = 1634 })

    // Write out the parts in the ResizeArray.  This will call the overridden ToString method
    // in the Part type
    printfn ""
    parts |> Seq.iter (fun p -> printfn "%O" p)

    // Check the ResizeArray for part #1734. This calls the IEquatable.Equals method 
    // of the Part type, which checks the PartId for equality.    
    printfn "\nContains(\"1734\"): %b" (parts.Contains({PartId=1734; PartName=""}))
    
    // Insert a new item at position 2.
    printfn "\nInsert(2, \"1834\")"
    parts.Insert(2, { PartName = "brake lever"; PartId = 1834 })

    // Write out all parts
    parts |> Seq.iter (fun p -> printfn "%O" p)

    printfn "\nParts[3]: %O" parts.[3]

    printfn "\nRemove(\"1534\")"
    // This will remove part 1534 even though the PartName is different, 
    // because the Equals method only checks PartId for equality.
    // Since Remove returns true or false, we need to ignore the result
    parts.Remove({PartId=1534; PartName="cogs"}) |> ignore

    // Write out all parts
    printfn ""
    parts |> Seq.iter (fun p -> printfn "%O" p)

    printfn "\nRemoveAt(3)"
    // This will remove the part at index 3.
    parts.RemoveAt(3)

    // Write out all parts
    printfn ""
    parts |> Seq.iter (fun p -> printfn "%O" p)

    0 // return an integer exit code

下列範例示範類型字串之泛型類別的 List<T> 數個屬性和方法。（如需複雜類型的範例 List<T> ，請參閱 Contains 方法。

無參數建構函式可用來建立具有預設容量的字串清單。屬性 Capacity 隨即顯示，然後使用 Add 方法新增數個專案。項目列出，並 Capacity 屬性和 Count 屬性再次顯示，以顯示容量已視需要增加。

方法 Contains 可用來測試清單中的專案是否存在， Insert 方法是用來在清單中間插入新專案，並再次顯示清單的內容。

默認 Item[] 屬性（C# 中的索引器）是用來擷取專案， Remove 方法是用來移除稍早新增之重複專案的第一個實例，並再次顯示內容。方法 Remove 一律會移除它遇到的第一個實例。

方法 TrimExcess 可用來減少容量以符合計數，並顯示 Capacity 和 Count 屬性。如果未使用的容量少於總容量的 10%，清單就不會重新調整大小。

最後，使用 Clear 方法從列表中移除所有專案，並顯示 Capacity 和 Count 屬性。

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

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

Console.WriteLine($"""\nContains("Deinonychus"): {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]: {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($"Capacity: {dinosaurs.Capacity}");
Console.WriteLine($"Count: {dinosaurs.Count}");

dinosaurs.Clear();
Console.WriteLine("\nClear()");
Console.WriteLine($"Capacity: {dinosaurs.Capacity}");
Console.WriteLine($"Count: {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
 */

Public Class Example2

    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
    *)

共用方式為

System.Collections.Generic.List<T> 類別

效能考量

F# 考量因素

範例

其他資源