ReadOnlyCollection<T>::Item Property
Gets the element at the specified index.
Assembly: mscorlib (in mscorlib.dll)
| Exception | Condition |
|---|---|
| ArgumentOutOfRangeException | 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<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 namespace System; using namespace System::Collections::Generic; using namespace System::Collections::ObjectModel; void main() { List<String^>^ dinosaurs = gcnew List<String^>(); dinosaurs->Add("Tyrannosaurus"); dinosaurs->Add("Amargasaurus"); dinosaurs->Add("Deinonychus"); dinosaurs->Add("Compsognathus"); ReadOnlyCollection<String^>^ readOnlyDinosaurs = gcnew ReadOnlyCollection<String^>(dinosaurs); Console::WriteLine(); for each(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(); for each( String^ dinosaur in readOnlyDinosaurs ) { Console::WriteLine(dinosaur); } array<String^>^ dinoArray = gcnew array<String^>(readOnlyDinosaurs->Count + 2); readOnlyDinosaurs->CopyTo(dinoArray, 1); Console::WriteLine("\nCopied array has {0} elements:", dinoArray->Length); for each( 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 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.