ArrayList::ReadOnly Method (ArrayList)
Returns a read-only ArrayList wrapper.
Assembly: mscorlib (in mscorlib.dll)
Parameters
- list
- Type: System.Collections::ArrayList
The ArrayList to wrap.
| Exception | Condition |
|---|---|
| ArgumentNullException | list is nullptr. |
To prevent any modifications to list, expose list only through this wrapper.
A collection that is read-only is simply a collection with a wrapper that prevents modifying the collection. If changes are made to the underlying collection, the read-only collection reflects those changes.
This method is an O(1) operation.
The following code example shows how to create a read-only wrapper around an ArrayList and how to determine if an ArrayList is read-only.
#using <system.dll> using namespace System; using namespace System::Collections; int main() { // Creates and initializes a new ArrayList. ArrayList^ myAL = gcnew ArrayList; myAL->Add( "red" ); myAL->Add( "orange" ); myAL->Add( "yellow" ); // Creates a read-only copy of the ArrayList. ArrayList^ myReadOnlyAL = ArrayList::ReadOnly( myAL ); // Displays whether the ArrayList is read-only or writable. Console::WriteLine( "myAL is {0}.", myAL->IsReadOnly ? (String^)"read-only" : "writable" ); Console::WriteLine( "myReadOnlyAL is {0}.", myReadOnlyAL->IsReadOnly ? (String^)"read-only" : "writable" ); // Displays the contents of both collections. Console::WriteLine( "\nInitially," ); Console::WriteLine( "The original ArrayList myAL contains:" ); for ( int i(0); i < myAL->Count; ++i ) Console::WriteLine( " {0}", static_cast<String^>(myAL[ i ]) ); Console::WriteLine( "The read-only ArrayList myReadOnlyAL contains:" ); for ( int i(0); i < myReadOnlyAL->Count; ++i ) Console::WriteLine( " {0}", static_cast<String^>(myReadOnlyAL[ i ]) ); // Adding an element to a read-only ArrayList throws an exception. Console::WriteLine( "\nTrying to add a new element to the read-only ArrayList:" ); try { myReadOnlyAL->Add( "green" ); } catch ( Exception^ myException ) { Console::WriteLine( String::Concat( "Exception: ", myException->ToString() ) ); } // Adding an element to the original ArrayList affects the read-only ArrayList. myAL->Add( "blue" ); // Displays the contents of both collections again. Console::WriteLine( "\nAfter adding a new element to the original ArrayList," ); Console::WriteLine( "The original ArrayList myAL contains:" ); for ( int i(0); i < myAL->Count; ++i ) Console::WriteLine( " {0}", static_cast<String^>(myAL[ i ]) ); Console::WriteLine( "The read-only ArrayList myReadOnlyAL contains:" ); for ( int i(0); i < myReadOnlyAL->Count; ++i ) Console::WriteLine( " {0}", static_cast<String^>(myReadOnlyAL[ i ]) ); } /* This code produces the following output. myAL is writable. myReadOnlyAL is read-only. Initially, The original ArrayList myAL contains: red orange yellow The read-only ArrayList myReadOnlyAL contains: red orange yellow Trying to add a new element to the read-only ArrayList: Exception: System.NotSupportedException: Collection is read-only. at System.Collections.ReadOnlyArrayList.Add(Object obj) at SamplesArrayList.Main() After adding a new element to the original ArrayList, The original ArrayList myAL contains: red orange yellow blue The read-only ArrayList myReadOnlyAL contains: red orange yellow blue */
Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98
The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.