Collection<T>.Add(T) Method

Reference

Definition

Namespace:: System.Collections.ObjectModel

Assembly:: System.Runtime.dll

Assembly:: mscorlib.dll

Assembly:: netstandard.dll

Source:: Collection.cs

Source:: Collection.cs

Source:: Collection.cs

Important

Some information relates to prerelease product that may be substantially modified before it’s released. Microsoft makes no warranties, express or implied, with respect to the information provided here.

Adds an object to the end of the Collection<T>.

public:
 virtual void Add(T item);

public void Add (T item);

abstract member Add : 'T -> unit
override this.Add : 'T -> unit

Public Sub Add (item As T)

Parameters

item: T

The object to be added to the end of the Collection<T>. The value can be null for reference types.

Implements

Add(T)

Examples

The following code example demonstrates many of the properties and methods of Collection<T>. The code example creates a collection of strings, uses the Add method to add several strings, displays the Count, and lists the strings. The example uses the IndexOf method to find the index of a string and the Contains method to determine whether a string is in the collection. The example inserts a string using the Insert method and retrieves and sets strings using the default Item[] property (the indexer in C#). The example removes strings by string identity using the Remove method and by index using the RemoveAt method. Finally, the Clear method is used to clear all strings from the collection.

using namespace System;
using namespace System::Collections::Generic;
using namespace System::Collections::ObjectModel;

public ref class Demo
{
public:
    static void Main()
    {
        Collection<String^>^ dinosaurs = gcnew Collection<String^>();

        dinosaurs->Add("Psitticosaurus");
        dinosaurs->Add("Caudipteryx");
        dinosaurs->Add("Compsognathus");
        dinosaurs->Add("Muttaburrasaurus");

        Console::WriteLine("{0} dinosaurs:", dinosaurs->Count);
        Display(dinosaurs);

        Console::WriteLine("\nIndexOf(\"Muttaburrasaurus\"): {0}",
            dinosaurs->IndexOf("Muttaburrasaurus"));

        Console::WriteLine("\nContains(\"Caudipteryx\"): {0}",
            dinosaurs->Contains("Caudipteryx"));

        Console::WriteLine("\nInsert(2, \"Nanotyrannus\")");
        dinosaurs->Insert(2, "Nanotyrannus");
        Display(dinosaurs);

        Console::WriteLine("\ndinosaurs[2]: {0}", dinosaurs[2]);

        Console::WriteLine("\ndinosaurs[2] = \"Microraptor\"");
        dinosaurs[2] = "Microraptor";
        Display(dinosaurs);

        Console::WriteLine("\nRemove(\"Microraptor\")");
        dinosaurs->Remove("Microraptor");
        Display(dinosaurs);

        Console::WriteLine("\nRemoveAt(0)");
        dinosaurs->RemoveAt(0);
        Display(dinosaurs);

        Console::WriteLine("\ndinosaurs.Clear()");
        dinosaurs->Clear();
        Console::WriteLine("Count: {0}", dinosaurs->Count);
    }

private:
    static void Display(Collection<String^>^ cs)
    {
        Console::WriteLine();
        for each( String^ item in cs )
        {
            Console::WriteLine(item);
        }
    }
};

int main()
{
    Demo::Main();
}

/* This code example produces the following output:

4 dinosaurs:

Psitticosaurus
Caudipteryx
Compsognathus
Muttaburrasaurus

IndexOf("Muttaburrasaurus"): 3

Contains("Caudipteryx"): True

Insert(2, "Nanotyrannus")

Psitticosaurus
Caudipteryx
Nanotyrannus
Compsognathus
Muttaburrasaurus

dinosaurs[2]: Nanotyrannus

dinosaurs[2] = "Microraptor"

Psitticosaurus
Caudipteryx
Microraptor
Compsognathus
Muttaburrasaurus

Remove("Microraptor")

Psitticosaurus
Caudipteryx
Compsognathus
Muttaburrasaurus

RemoveAt(0)

Caudipteryx
Compsognathus
Muttaburrasaurus

dinosaurs.Clear()
Count: 0
 */

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;

public class Demo
{
    public static void Main()
    {
        Collection<string> dinosaurs = new Collection<string>();

        dinosaurs.Add("Psitticosaurus");
        dinosaurs.Add("Caudipteryx");
        dinosaurs.Add("Compsognathus");
        dinosaurs.Add("Muttaburrasaurus");

        Console.WriteLine("{0} dinosaurs:", dinosaurs.Count);
        Display(dinosaurs);

        Console.WriteLine("\nIndexOf(\"Muttaburrasaurus\"): {0}",
            dinosaurs.IndexOf("Muttaburrasaurus"));

        Console.WriteLine("\nContains(\"Caudipteryx\"): {0}",
            dinosaurs.Contains("Caudipteryx"));

        Console.WriteLine("\nInsert(2, \"Nanotyrannus\")");
        dinosaurs.Insert(2, "Nanotyrannus");
        Display(dinosaurs);

        Console.WriteLine("\ndinosaurs[2]: {0}", dinosaurs[2]);

        Console.WriteLine("\ndinosaurs[2] = \"Microraptor\"");
        dinosaurs[2] = "Microraptor";
        Display(dinosaurs);

        Console.WriteLine("\nRemove(\"Microraptor\")");
        dinosaurs.Remove("Microraptor");
        Display(dinosaurs);

        Console.WriteLine("\nRemoveAt(0)");
        dinosaurs.RemoveAt(0);
        Display(dinosaurs);

        Console.WriteLine("\ndinosaurs.Clear()");
        dinosaurs.Clear();
        Console.WriteLine("Count: {0}", dinosaurs.Count);
    }

    private static void Display(Collection<string> cs)
    {
        Console.WriteLine();
        foreach( string item in cs )
        {
            Console.WriteLine(item);
        }
    }
}

/* This code example produces the following output:

4 dinosaurs:

Psitticosaurus
Caudipteryx
Compsognathus
Muttaburrasaurus

IndexOf("Muttaburrasaurus"): 3

Contains("Caudipteryx"): True

Insert(2, "Nanotyrannus")

Psitticosaurus
Caudipteryx
Nanotyrannus
Compsognathus
Muttaburrasaurus

dinosaurs[2]: Nanotyrannus

dinosaurs[2] = "Microraptor"

Psitticosaurus
Caudipteryx
Microraptor
Compsognathus
Muttaburrasaurus

Remove("Microraptor")

Psitticosaurus
Caudipteryx
Compsognathus
Muttaburrasaurus

RemoveAt(0)

Caudipteryx
Compsognathus
Muttaburrasaurus

dinosaurs.Clear()
Count: 0
 */

Imports System.Collections.Generic
Imports System.Collections.ObjectModel

Public Class Demo
    
    Public Shared Sub Main() 

        Dim dinosaurs As New Collection(Of String)

        dinosaurs.Add("Psitticosaurus")
        dinosaurs.Add("Caudipteryx")
        dinosaurs.Add("Compsognathus")
        dinosaurs.Add("Muttaburrasaurus")

        Console.WriteLine("{0} dinosaurs:", dinosaurs.Count)
        Display(dinosaurs)
    
        Console.WriteLine(vbLf & "IndexOf(""Muttaburrasaurus""): {0}", _
            dinosaurs.IndexOf("Muttaburrasaurus"))

        Console.WriteLine(vbLf & "Contains(""Caudipteryx""): {0}", _
            dinosaurs.Contains("Caudipteryx"))

        Console.WriteLine(vbLf & "Insert(2, ""Nanotyrannus"")")
        dinosaurs.Insert(2, "Nanotyrannus")
        Display(dinosaurs)

        Console.WriteLine(vbLf & "dinosaurs(2): {0}", dinosaurs(2))

        Console.WriteLine(vbLf & "dinosaurs(2) = ""Microraptor""")
        dinosaurs(2) = "Microraptor"
        Display(dinosaurs)

        Console.WriteLine(vbLf & "Remove(""Microraptor"")")
        dinosaurs.Remove("Microraptor")
        Display(dinosaurs)

        Console.WriteLine(vbLf & "RemoveAt(0)")
        dinosaurs.RemoveAt(0)
        Display(dinosaurs)
 
        Console.WriteLine(vbLf & "dinosaurs.Clear()")
        dinosaurs.Clear()
        Console.WriteLine("Count: {0}", dinosaurs.Count)

    End Sub
    
    Private Shared Sub Display(ByVal cs As Collection(Of String)) 
        Console.WriteLine()
        For Each item As String In cs
            Console.WriteLine(item)
        Next item
    End Sub
End Class

' This code example produces the following output:
'
'4 dinosaurs:
'
'Psitticosaurus
'Caudipteryx
'Compsognathus
'Muttaburrasaurus
'
'IndexOf("Muttaburrasaurus"): 3
'
'Contains("Caudipteryx"): True
'
'Insert(2, "Nanotyrannus")
'
'Psitticosaurus
'Caudipteryx
'Nanotyrannus
'Compsognathus
'Muttaburrasaurus
'
'dinosaurs(2): Nanotyrannus
'
'dinosaurs(2) = "Microraptor"
'
'Psitticosaurus
'Caudipteryx
'Microraptor
'Compsognathus
'Muttaburrasaurus
'
'Remove("Microraptor")
'
'Psitticosaurus
'Caudipteryx
'Compsognathus
'Muttaburrasaurus
'
'RemoveAt(0)
'
'Caudipteryx
'Compsognathus
'Muttaburrasaurus
'
'dinosaurs.Clear()
'Count: 0

Remarks

Collection<T> accepts null as a valid value for reference types and allows duplicate elements.

This method is an O(1) operation.

Applies to

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