ReadOnlyCollection.Item Property
Assembly: mscorlib (in mscorlib.dll)
| Exception type | Condition |
|---|---|
| index is less than zero. -or- index is equal to or greater than Count. |
This property provides the ability to access a specific element in the collection by using the following C# syntax: myCollection[index] (myCollection(index) in Visual Basic).
The C# language uses the this keyword to define the indexers instead of implementing the Item property. Visual Basic implements Item as a default property, which provides the same indexing functionality.
Retrieving the value of this property is an O(1) operation.
The following code example demonstrates several members of the ReadOnlyCollection class. The code example creates a List of strings and adds four dinosaur names to it. The code example then wraps the list in a ReadOnlyCollection.
After demonstrating the Count, Contains, Item, and System#Collections#IList#IndexOf members, the code example shows that the ReadOnlyCollection is just a wrapper for the original List by adding a new item to the List and displaying the contents of the ReadOnlyCollection.
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" "" */
Windows 98, Windows Server 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition
The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.