ReadOnlyCollectionBase Class
Assembly: mscorlib (in mscorlib.dll)
'Declaration <SerializableAttribute> _ <ComVisibleAttribute(True)> _ Public MustInherit Class ReadOnlyCollectionBase Implements ICollection, IEnumerable 'Usage Dim instance As ReadOnlyCollectionBase
/** @attribute SerializableAttribute() */ /** @attribute ComVisibleAttribute(true) */ public abstract class ReadOnlyCollectionBase implements ICollection, IEnumerable
SerializableAttribute ComVisibleAttribute(true) public abstract class ReadOnlyCollectionBase implements ICollection, IEnumerable
Not applicable.
A ReadOnlyCollectionBase instance is always read-only. See CollectionBase for a modifiable version of this class.
Notes to Implementers: This base class is provided to make it easier for implementers to create a strongly typed read-only custom collection. Implementers are encouraged to extend this base class instead of creating their own. Members of this base class are protected and are intended to be used through a derived class only. This class makes the underlying collection available through the InnerList property, which is intended for use only by classes that are derived directly from ReadOnlyCollectionBase. The derived class must ensure that its own users cannot modify the underlying collection.The following code example implements the ReadOnlyCollectionBase class.
Imports System Imports System.Collections Public Class ROCollection Inherits ReadOnlyCollectionBase Public Sub New(sourceList As IList) InnerList.AddRange(sourceList) End Sub 'New Default Public ReadOnly Property Item(index As Integer) As [Object] Get Return InnerList(index) End Get End Property Public Function IndexOf(value As [Object]) As Integer Return InnerList.IndexOf(value) End Function 'IndexOf Public Function Contains(value As [Object]) As Boolean Return InnerList.Contains(value) End Function 'Contains End Class 'ROCollection Public Class SamplesCollectionBase Public Shared Sub Main() ' Create an ArrayList. Dim myAL As New ArrayList() myAL.Add("red") myAL.Add("blue") myAL.Add("yellow") myAL.Add("green") myAL.Add("orange") myAL.Add("purple") ' Create a new ROCollection that contains the elements in myAL. Dim myCol As New ROCollection(myAL) ' Display the contents of the collection using For Each. This is the preferred method. Console.WriteLine("Contents of the collection (using For Each):") PrintValues1(myCol) ' Display the contents of the collection using the enumerator. Console.WriteLine("Contents of the collection (using enumerator):") PrintValues2(myCol) ' Display the contents of the collection using the Count property and the Item property. Console.WriteLine("Contents of the collection (using Count and Item):") PrintIndexAndValues(myCol) ' Search the collection with Contains and IndexOf. Console.WriteLine("Contains yellow: {0}", myCol.Contains("yellow")) Console.WriteLine("orange is at index {0}.", myCol.IndexOf("orange")) Console.WriteLine() End Sub 'Main ' Uses the Count property and the Item property. Public Shared Sub PrintIndexAndValues(myCol As ROCollection) Dim i As Integer For i = 0 To myCol.Count - 1 Console.WriteLine(" [{0}]: {1}", i, myCol(i)) Next i Console.WriteLine() End Sub 'PrintIndexAndValues ' Uses the For Each statement which hides the complexity of the enumerator. ' NOTE: The For Each statement is the preferred way of enumerating the contents of a collection. Public Shared Sub PrintValues1(myCol As ROCollection) Dim obj As [Object] For Each obj In myCol Console.WriteLine(" {0}", obj) Next obj Console.WriteLine() End Sub 'PrintValues1 ' Uses the enumerator. ' NOTE: The For Each statement is the preferred way of enumerating the contents of a collection. Public Shared Sub PrintValues2(myCol As ROCollection) Dim myEnumerator As System.Collections.IEnumerator = myCol.GetEnumerator() While myEnumerator.MoveNext() Console.WriteLine(" {0}", myEnumerator.Current) End While Console.WriteLine() End Sub 'PrintValues2 End Class 'SamplesCollectionBase 'This code produces the following output. ' 'Contents of the collection (using For Each): ' red ' blue ' yellow ' green ' orange ' purple ' 'Contents of the collection (using enumerator): ' red ' blue ' yellow ' green ' orange ' purple ' 'Contents of the collection (using Count and Item): ' [0]: red ' [1]: blue ' [2]: yellow ' [3]: green ' [4]: orange ' [5]: purple ' 'Contains yellow: True 'orange is at index 4.
import System.*;
import System.Collections.*;
public class ROCollection extends ReadOnlyCollectionBase
{
public ROCollection(IList sourceList)
{
get_InnerList().AddRange(sourceList);
} //ROCollection
/** @property
*/
public Object get_Item(int index)
{
return get_InnerList().get_Item(index);
} //get_Item
public int IndexOf(Object value)
{
return get_InnerList().IndexOf(value);
} //IndexOf
public boolean Contains(Object value)
{
return get_InnerList().Contains(value);
} //Contains
} //ROCollection
public class SamplesCollectionBase
{
public static void main(String[] args)
{
// Create an ArrayList.
ArrayList myAL = new ArrayList();
myAL.Add("red");
myAL.Add("blue");
myAL.Add("yellow");
myAL.Add("green");
myAL.Add("orange");
myAL.Add("purple");
// Create a new ROCollection that contains the elements in myAL.
ROCollection myCol = new ROCollection(myAL);
// Display the contents of the collection using for. This is the
// preferred method.
Console.WriteLine("Contents of the collection (using for):");
PrintValues1(myCol);
// Display the contents of the collection using the enumerator.
Console.WriteLine("Contents of the collection (using enumerator):");
PrintValues2(myCol);
// Display the contents of the collection using the Count property and
// the Item property.
Console.WriteLine("Contents of the collection (using Count and Item):");
PrintIndexAndValues(myCol);
// Search the collection with Contains and IndexOf.
Console.WriteLine("Contains yellow: {0}",
(System.Boolean)myCol.Contains("yellow"));
Console.WriteLine("orange is at index {0}.",
(Int32)myCol.IndexOf("orange"));
Console.WriteLine();
} //main
// Uses the Count property and the Item property.
public static void PrintIndexAndValues(ROCollection myCol)
{
for(int i = 0; i < myCol.get_Count(); i++) {
Console.WriteLine(" [{0}]: {1}",(Int32)i, myCol.get_Item(i));
}
Console.WriteLine();
} //PrintIndexAndValues
// Uses the for statement which hides the complexity of the enumerator.
// NOTE: The for statement is the preferred way of enumerating the contents
// of a collection.
public static void PrintValues1(ROCollection myCol)
{
for (int iCtr = 0; iCtr < myCol.get_Count(); iCtr++ ) {
Object obj = myCol.get_Item(iCtr);
Console.WriteLine(" {0}", obj);
}
Console.WriteLine();
} //PrintValues1
// Uses the enumerator.
// NOTE: The for statement is the preferred way of enumerating the
// contents of a collection.
public static void PrintValues2(ROCollection myCol)
{
System.Collections.IEnumerator myEnumerator = myCol.GetEnumerator();
while(myEnumerator.MoveNext()) {
Console.WriteLine(" {0}", myEnumerator.get_Current());
}
Console.WriteLine();
} //PrintValues2
} //SamplesCollectionBase
/*
This code produces the following output.
Contents of the collection (using for):
red
blue
yellow
green
orange
purple
Contents of the collection (using enumerator):
red
blue
yellow
green
orange
purple
Contents of the collection (using Count and Item):
[0]: red
[1]: blue
[2]: yellow
[3]: green
[4]: orange
[5]: purple
Contains yellow: True
orange is at index 4.
*/
Public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.
This implementation does not provide a synchronized (thread safe) wrapper for a ReadOnlyCollectionBase, but derived classes can create their own synchronized versions of the ReadOnlyCollectionBase using the SyncRoot property.
Enumerating through a collection is intrinsically not a thread-safe procedure. Even when a collection is synchronized, other threads can still modify the collection, which causes the enumerator to throw an exception. To guarantee thread safety during enumeration, you can either lock the collection during the entire enumeration or catch the exceptions resulting from changes made by other threads.
Windows 98, Windows Server 2000 SP4, Windows Millennium Edition, 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.