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link之家  ›  List<t>.Add(T) 方法 (System.Collections.Generic) | Microsoft Learn</t>
string each
https://learn.microsoft.com/zh-cn/dotnet/api/system.collections.generic.list-1.add?view=net-8.0
仗义的人字拖
2 月前 
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 = new List<Part>();
        // Add parts to the list.
        parts.Add(new Part() { PartName = "crank arm", PartId = 1234 });
        parts.Add(new Part() { PartName = "chain ring", PartId = 1334 });
        parts.Add(new Part() { PartName = "regular seat", PartId = 1434 });
        parts.Add(new Part() { PartName = "banana seat", PartId = 1444 });
        parts.Add(new Part() { PartName = "cassette", PartId = 1534 });
        parts.Add(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("\nContains(\"1734\"): {0}",
        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]: {0}", 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

Imports 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
    Implements IEquatable(Of Part)
    Public Property PartName() As String
            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
            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
            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)
        ' 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)
        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)
        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)
    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

以下示例演示泛型类的 List<T> 多个属性和方法，包括 Add 方法。 无参数构造函数用于创建容量为 0 的字符串列表。 显示 Capacity 属性，然后使用 Add 方法添加多个项。 将列出项，并 Capacity 再次显示 属性以及 Count 属性，以显示容量已根据需要增加。




    



其他属性和方法用于搜索、插入和删除列表中的元素，最后清除列表。


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)
        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)
        ' 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)
        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
	
List<T> 接受 null 作为引用类型的有效值，并允许重复元素。


如果 Count 已等于 Capacity，则通过自动重新分配内部数组来增加 的容量 List<T> ，并在添加新元素之前将现有元素复制到新数组。


如果 Count 小于 Capacity，则此方法为 O (1) 运算。 如果需要增加容量以适应新元素，此方法将成为 O (n) 操作，其中 n 为 Count。
 
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