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ReadOnlyCollection<T>.CopyTo Method

Copies the entire ReadOnlyCollection<T> to a compatible one-dimensional Array, starting at the specified index of the target array.

Namespace:  System.Collections.ObjectModel
Assembly:  mscorlib (in mscorlib.dll)

public void CopyTo(
	T[] array,
	int index
)

Parameters

array
Type: T[]

The one-dimensional Array that is the destination of the elements copied from ReadOnlyCollection<T>. The Array must have zero-based indexing.

index
Type: System.Int32

The zero-based index in array at which copying begins.

Implements

ICollection<T>.CopyTo(T[], Int32)

ExceptionCondition
ArgumentNullException

array is null.

ArgumentOutOfRangeException

index is less than zero.

ArgumentException

The number of elements in the source ReadOnlyCollection<T> is greater than the available space from index to the end of the destination array.

This method uses Array.Copy to copy the elements.

The elements are copied to the Array in the same order that the enumerator iterates through the ReadOnlyCollection<T>.

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

The following code example demonstrates several members of the ReadOnlyCollection<T> class. The code example creates a List<T> of strings and adds four dinosaur names to it. The code example then wraps the list in a ReadOnlyCollection<T>.

After demonstrating the Count, Contains, Item, and IList.IndexOf members, the code example shows that the ReadOnlyCollection<T> is just a wrapper for the original List<T> by adding a new item to the List<T> and displaying the contents of the ReadOnlyCollection<T>.

Finally, the code example creates an array larger than the collection and uses the CopyTo method to insert the elements of the collection into the middle of the array.

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

public class Example
{
    public static void Main()
    {
        List<string> dinosaurs = new List<string>();

        dinosaurs.Add("Tyrannosaurus");
        dinosaurs.Add("Amargasaurus");
        dinosaurs.Add("Deinonychus");
        dinosaurs.Add("Compsognathus");

        ReadOnlyCollection<string> readOnlyDinosaurs = 
            new ReadOnlyCollection<string>(dinosaurs);

        Console.WriteLine();
        foreach( string dinosaur in readOnlyDinosaurs )
        {
            Console.WriteLine(dinosaur);
        }

        Console.WriteLine("\nCount: {0}", readOnlyDinosaurs.Count);

        Console.WriteLine("\nContains(\"Deinonychus\"): {0}", 
            readOnlyDinosaurs.Contains("Deinonychus"));

        Console.WriteLine("\nreadOnlyDinosaurs[3]: {0}", 
            readOnlyDinosaurs[3]);

        Console.WriteLine("\nIndexOf(\"Compsognathus\"): {0}", 
            readOnlyDinosaurs.IndexOf("Compsognathus"));

        Console.WriteLine("\nInsert into the wrapped List:");
        Console.WriteLine("Insert(2, \"Oviraptor\")");
        dinosaurs.Insert(2, "Oviraptor");

        Console.WriteLine();
        foreach( string dinosaur in readOnlyDinosaurs )
        {
            Console.WriteLine(dinosaur);
        }

        string[] dinoArray = new string[readOnlyDinosaurs.Count + 2];
        readOnlyDinosaurs.CopyTo(dinoArray, 1);

        Console.WriteLine("\nCopied array has {0} elements:", 
            dinoArray.Length);
        foreach( string dinosaur in dinoArray )
        {
            Console.WriteLine("\"{0}\"", dinosaur);
        }
    }
}

/* This code example produces the following output:

Tyrannosaurus
Amargasaurus
Deinonychus
Compsognathus

Count: 4

Contains("Deinonychus"): True

readOnlyDinosaurs[3]: Compsognathus

IndexOf("Compsognathus"): 3

Insert into the wrapped List:
Insert(2, "Oviraptor")

Tyrannosaurus
Amargasaurus
Oviraptor
Deinonychus
Compsognathus

Copied array has 7 elements:
""
"Tyrannosaurus"
"Amargasaurus"
"Oviraptor"
"Deinonychus"
"Compsognathus"
""
 */

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0, 2.0, 1.0

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Portable Class Library

Supported in: Portable Class Library
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