KeyedCollection<TKey,TItem>.ClearItems Method
Definition
Important
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Removes all elements from the KeyedCollection<TKey,TItem>.
protected:
override void ClearItems();protected override void ClearItems ();override this.ClearItems : unit -> unitProtected Overrides Sub ClearItems ()Examples
This section contains two code examples that demonstrate overriding the ClearItems method to provide custom behavior for clearing all objects from the collection. The first example adds a custom notification event and the second provides support for a collection of objects with mutable keys.
Example 1
The following code example shows how to override the protected InsertItem, RemoveItem, ClearItems, and SetItem methods, to provide custom behavior for the Add, Remove, and Clear methods, and for setting the default Item[] property (the indexer in C#). The custom behavior provided in this example is a notification event named Changed, which is raised at the end of each of the overridden methods.
The code example creates the SimpleOrder class, which derives from KeyedCollection<TKey,TItem> and represents a simple order form. The order form contains OrderItem objects representing items ordered. The code example also creates a SimpleOrderChangedEventArgs class to contain the event information, and an enumeration to identify the type of change.
The code example demonstrates the custom behavior by calling the properties and methods of the derived class, in the Main method of the Demo class.
This code example uses objects with immutable keys. For a code example that uses mutable keys, see ChangeItemKey.
using namespace System;
using namespace System::Collections::Generic;
using namespace System::Collections::ObjectModel;
public enum class ChangeTypes
{
Added,
Removed,
Replaced,
Cleared
};
ref class SimpleOrderChangedEventArgs;
// This class represents a simple line item in an order. All the
// values are immutable except quantity.
//
public ref class OrderItem
{
private:
int _quantity;
public:
initonly int PartNumber;
initonly String^ Description;
initonly double UnitPrice;
OrderItem(int partNumber, String^ description, int quantity,
double unitPrice)
{
this->PartNumber = partNumber;
this->Description = description;
this->Quantity = quantity;
this->UnitPrice = unitPrice;
};
property int Quantity
{
int get() { return _quantity; };
void set(int value)
{
if (value < 0)
throw gcnew ArgumentException("Quantity cannot be negative.");
_quantity = value;
};
};
virtual String^ ToString() override
{
return String::Format(
"{0,9} {1,6} {2,-12} at {3,8:#,###.00} = {4,10:###,###.00}",
PartNumber, _quantity, Description, UnitPrice,
UnitPrice * _quantity);
};
};
// Event argument for the Changed event.
//
public ref class SimpleOrderChangedEventArgs : EventArgs
{
public:
OrderItem^ ChangedItem;
initonly ChangeTypes ChangeType;
OrderItem^ ReplacedWith;
SimpleOrderChangedEventArgs(ChangeTypes change,
OrderItem^ item, OrderItem^ replacement)
{
this->ChangeType = change;
this->ChangedItem = item;
this->ReplacedWith = replacement;
}
};
// This class derives from KeyedCollection and shows how to override
// the protected ClearItems, InsertItem, RemoveItem, and SetItem
// methods in order to change the behavior of the default Item
// property and the Add, Clear, Insert, and Remove methods. The
// class implements a Changed event, which is raised by all the
// protected methods.
//
// SimpleOrder is a collection of OrderItem objects, and its key
// is the PartNumber field of OrderItem-> PartNumber is an Integer,
// so SimpleOrder inherits KeyedCollection<int, OrderItem>.
// (Note that the key of OrderItem cannot be changed; if it could
// be changed, SimpleOrder would have to override ChangeItemKey.)
//
public ref class SimpleOrder : KeyedCollection<int, OrderItem^>
{
public:
event EventHandler<SimpleOrderChangedEventArgs^>^ Changed;
// This parameterless constructor calls the base class constructor
// that specifies a dictionary threshold of 0, so that the internal
// dictionary is created as soon as an item is added to the
// collection.
//
SimpleOrder() : KeyedCollection<int, OrderItem^>(nullptr, 0) {};
// This is the only method that absolutely must be overridden,
// because without it the KeyedCollection cannot extract the
// keys from the items.
//
protected:
virtual int GetKeyForItem(OrderItem^ item) override
{
// In this example, the key is the part number.
return item->PartNumber;
}
virtual void InsertItem(int index, OrderItem^ newItem) override
{
__super::InsertItem(index, newItem);
Changed(this, gcnew SimpleOrderChangedEventArgs(
ChangeTypes::Added, newItem, nullptr));
}
virtual void SetItem(int index, OrderItem^ newItem) override
{
OrderItem^ replaced = this->Items[index];
__super::SetItem(index, newItem);
Changed(this, gcnew SimpleOrderChangedEventArgs(
ChangeTypes::Replaced, replaced, newItem));
}
virtual void RemoveItem(int index) override
{
OrderItem^ removedItem = Items[index];
__super::RemoveItem(index);
Changed(this, gcnew SimpleOrderChangedEventArgs(
ChangeTypes::Removed, removedItem, nullptr));
}
virtual void ClearItems() override
{
__super::ClearItems();
Changed(this, gcnew SimpleOrderChangedEventArgs(
ChangeTypes::Cleared, nullptr, nullptr));
}
// This method uses the internal reference to the dictionary
// to test fo
public:
void AddOrMerge(OrderItem^ newItem)
{
int key = this->GetKeyForItem(newItem);
OrderItem^ existingItem = nullptr;
// The dictionary is not created until the first item is
// added, so it is necessary to test for null. Using
// AndAlso ensures that TryGetValue is not called if the
// dictionary does not exist.
//
if (this->Dictionary != nullptr &&
this->Dictionary->TryGetValue(key, existingItem))
{
existingItem->Quantity += newItem->Quantity;
}
else
{
this->Add(newItem);
}
}
};
public ref class Demo
{
public:
static void Main()
{
SimpleOrder^ weekly = gcnew SimpleOrder();
weekly->Changed += gcnew
EventHandler<SimpleOrderChangedEventArgs^>(ChangedHandler);
// The Add method, inherited from Collection, takes OrderItem->
//
weekly->Add(gcnew OrderItem(110072674, "Widget", 400, 45.17));
weekly->Add(gcnew OrderItem(110072675, "Sprocket", 27, 5.3));
weekly->Add(gcnew OrderItem(101030411, "Motor", 10, 237.5));
weekly->Add(gcnew OrderItem(110072684, "Gear", 175, 5.17));
Display(weekly);
// The Contains method of KeyedCollection takes TKey.
//
Console::WriteLine("\nContains(101030411): {0}",
weekly->Contains(101030411));
// The default Item property of KeyedCollection takes the key
// type, Integer. The property is read-only.
//
Console::WriteLine("\nweekly[101030411]->Description: {0}",
weekly[101030411]->Description);
// The Remove method of KeyedCollection takes a key.
//
Console::WriteLine("\nRemove(101030411)");
weekly->Remove(101030411);
// The Insert method, inherited from Collection, takes an
// index and an OrderItem.
//
Console::WriteLine("\nInsert(2, gcnew OrderItem(...))");
weekly->Insert(2, gcnew OrderItem(111033401, "Nut", 10, .5));
// The default Item property is overloaded. One overload comes
// from KeyedCollection<int, OrderItem>; that overload
// is read-only, and takes Integer because it retrieves by key.
// The other overload comes from Collection<OrderItem>, the
// base class of KeyedCollection<int, OrderItem>; it
// retrieves by index, so it also takes an Integer. The compiler
// uses the most-derived overload, from KeyedCollection, so the
// only way to access SimpleOrder by index is to cast it to
// Collection<OrderItem>. Otherwise the index is interpreted
// as a key, and KeyNotFoundException is thrown.
//
Collection<OrderItem^>^ coweekly = weekly;
Console::WriteLine("\ncoweekly[2].Description: {0}",
coweekly[2]->Description);
Console::WriteLine("\ncoweekly[2] = gcnew OrderItem(...)");
coweekly[2] = gcnew OrderItem(127700026, "Crank", 27, 5.98);
OrderItem^ temp = coweekly[2];
// The IndexOf method, inherited from Collection<OrderItem>,
// takes an OrderItem instead of a key.
//
Console::WriteLine("\nIndexOf(temp): {0}", weekly->IndexOf(temp));
// The inherited Remove method also takes an OrderItem->
//
Console::WriteLine("\nRemove(temp)");
weekly->Remove(temp);
Console::WriteLine("\nRemoveAt(0)");
weekly->RemoveAt(0);
weekly->AddOrMerge(gcnew OrderItem(110072684, "Gear", 1000, 5.17));
Display(weekly);
Console::WriteLine();
weekly->Clear();
}
private:
static void Display(SimpleOrder^ order)
{
Console::WriteLine();
for each( OrderItem^ item in order )
{
Console::WriteLine(item);
}
}
static void ChangedHandler(Object^ source,
SimpleOrderChangedEventArgs^ e)
{
OrderItem^ item = e->ChangedItem;
if (e->ChangeType == ChangeTypes::Replaced)
{
OrderItem^ replacement = e->ReplacedWith;
Console::WriteLine("{0} (quantity {1}) was replaced " +
"by {2}, (quantity {3}).", item->Description,
item->Quantity, replacement->Description,
replacement->Quantity);
}
else if(e->ChangeType == ChangeTypes::Cleared)
{
Console::WriteLine("The order list was cleared.");
}
else
{
Console::WriteLine("{0} (quantity {1}) was {2}.",
item->Description, item->Quantity, e->ChangeType);
}
}
};
void main()
{
Demo::Main();
}
/* This code example produces the following output:
Widget (quantity 400) was Added.
Sprocket (quantity 27) was Added.
Motor (quantity 10) was Added.
Gear (quantity 175) was Added.
110072674 400 Widget at 45.17 = 18,068.00
110072675 27 Sprocket at 5.30 = 143.10
101030411 10 Motor at 237.50 = 2,375.00
110072684 175 Gear at 5.17 = 904.75
Contains(101030411): True
weekly[101030411]->Description: Motor
Remove(101030411)
Motor (quantity 10) was Removed.
Insert(2, gcnew OrderItem(...))
Nut (quantity 10) was Added.
coweekly[2].Description: Nut
coweekly[2] = gcnew OrderItem(...)
Nut (quantity 10) was replaced by Crank, (quantity 27).
IndexOf(temp): 2
Remove(temp)
Crank (quantity 27) was Removed.
RemoveAt(0)
Widget (quantity 400) was Removed.
110072675 27 Sprocket at 5.30 = 143.10
110072684 1175 Gear at 5.17 = 6,074.75
The order list was cleared.
*/
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
// This class derives from KeyedCollection and shows how to override
// the protected ClearItems, InsertItem, RemoveItem, and SetItem
// methods in order to change the behavior of the default Item
// property and the Add, Clear, Insert, and Remove methods. The
// class implements a Changed event, which is raised by all the
// protected methods.
//
// SimpleOrder is a collection of OrderItem objects, and its key
// is the PartNumber field of OrderItem. PartNumber is an Integer,
// so SimpleOrder inherits KeyedCollection<int, OrderItem>.
// (Note that the key of OrderItem cannot be changed; if it could
// be changed, SimpleOrder would have to override ChangeItemKey.)
//
public class SimpleOrder : KeyedCollection<int, OrderItem>
{
public event EventHandler<SimpleOrderChangedEventArgs> Changed;
// This parameterless constructor calls the base class constructor
// that specifies a dictionary threshold of 0, so that the internal
// dictionary is created as soon as an item is added to the
// collection.
//
public SimpleOrder() : base(null, 0) {}
// This is the only method that absolutely must be overridden,
// because without it the KeyedCollection cannot extract the
// keys from the items.
//
protected override int GetKeyForItem(OrderItem item)
{
// In this example, the key is the part number.
return item.PartNumber;
}
protected override void InsertItem(int index, OrderItem newItem)
{
base.InsertItem(index, newItem);
EventHandler<SimpleOrderChangedEventArgs> temp = Changed;
if (temp != null)
{
temp(this, new SimpleOrderChangedEventArgs(
ChangeType.Added, newItem, null));
}
}
protected override void SetItem(int index, OrderItem newItem)
{
OrderItem replaced = Items[index];
base.SetItem(index, newItem);
EventHandler<SimpleOrderChangedEventArgs> temp = Changed;
if (temp != null)
{
temp(this, new SimpleOrderChangedEventArgs(
ChangeType.Replaced, replaced, newItem));
}
}
protected override void RemoveItem(int index)
{
OrderItem removedItem = Items[index];
base.RemoveItem(index);
EventHandler<SimpleOrderChangedEventArgs> temp = Changed;
if (temp != null)
{
temp(this, new SimpleOrderChangedEventArgs(
ChangeType.Removed, removedItem, null));
}
}
protected override void ClearItems()
{
base.ClearItems();
EventHandler<SimpleOrderChangedEventArgs> temp = Changed;
if (temp != null)
{
temp(this, new SimpleOrderChangedEventArgs(
ChangeType.Cleared, null, null));
}
}
}
// Event argument for the Changed event.
//
public class SimpleOrderChangedEventArgs : EventArgs
{
private OrderItem _changedItem;
private ChangeType _changeType;
private OrderItem _replacedWith;
public OrderItem ChangedItem { get { return _changedItem; }}
public ChangeType ChangeType { get { return _changeType; }}
public OrderItem ReplacedWith { get { return _replacedWith; }}
public SimpleOrderChangedEventArgs(ChangeType change,
OrderItem item, OrderItem replacement)
{
_changeType = change;
_changedItem = item;
_replacedWith = replacement;
}
}
public enum ChangeType
{
Added,
Removed,
Replaced,
Cleared
};
public class Demo
{
public static void Main()
{
SimpleOrder weekly = new SimpleOrder();
weekly.Changed += new
EventHandler<SimpleOrderChangedEventArgs>(ChangedHandler);
// The Add method, inherited from Collection, takes OrderItem.
//
weekly.Add(new OrderItem(110072674, "Widget", 400, 45.17));
weekly.Add(new OrderItem(110072675, "Sprocket", 27, 5.3));
weekly.Add(new OrderItem(101030411, "Motor", 10, 237.5));
weekly.Add(new OrderItem(110072684, "Gear", 175, 5.17));
Display(weekly);
// The Contains method of KeyedCollection takes TKey.
//
Console.WriteLine("\nContains(101030411): {0}",
weekly.Contains(101030411));
// The default Item property of KeyedCollection takes the key
// type, Integer. The property is read-only.
//
Console.WriteLine("\nweekly[101030411].Description: {0}",
weekly[101030411].Description);
// The Remove method of KeyedCollection takes a key.
//
Console.WriteLine("\nRemove(101030411)");
weekly.Remove(101030411);
// The Insert method, inherited from Collection, takes an
// index and an OrderItem.
//
Console.WriteLine("\nInsert(2, new OrderItem(...))");
weekly.Insert(2, new OrderItem(111033401, "Nut", 10, .5));
// The default Item property is overloaded. One overload comes
// from KeyedCollection<int, OrderItem>; that overload
// is read-only, and takes Integer because it retrieves by key.
// The other overload comes from Collection<OrderItem>, the
// base class of KeyedCollection<int, OrderItem>; it
// retrieves by index, so it also takes an Integer. The compiler
// uses the most-derived overload, from KeyedCollection, so the
// only way to access SimpleOrder by index is to cast it to
// Collection<OrderItem>. Otherwise the index is interpreted
// as a key, and KeyNotFoundException is thrown.
//
Collection<OrderItem> coweekly = weekly;
Console.WriteLine("\ncoweekly[2].Description: {0}",
coweekly[2].Description);
Console.WriteLine("\ncoweekly[2] = new OrderItem(...)");
coweekly[2] = new OrderItem(127700026, "Crank", 27, 5.98);
OrderItem temp = coweekly[2];
// The IndexOf method, inherited from Collection<OrderItem>,
// takes an OrderItem instead of a key.
//
Console.WriteLine("\nIndexOf(temp): {0}", weekly.IndexOf(temp));
// The inherited Remove method also takes an OrderItem.
//
Console.WriteLine("\nRemove(temp)");
weekly.Remove(temp);
Console.WriteLine("\nRemoveAt(0)");
weekly.RemoveAt(0);
// Increase the quantity for a line item.
Console.WriteLine("\ncoweekly(1) = New OrderItem(...)");
coweekly[1] = new OrderItem(coweekly[1].PartNumber,
coweekly[1].Description, coweekly[1].Quantity + 1000,
coweekly[1].UnitPrice);
Display(weekly);
Console.WriteLine();
weekly.Clear();
}
private static void Display(SimpleOrder order)
{
Console.WriteLine();
foreach( OrderItem item in order )
{
Console.WriteLine(item);
}
}
private static void ChangedHandler(object source,
SimpleOrderChangedEventArgs e)
{
OrderItem item = e.ChangedItem;
if (e.ChangeType==ChangeType.Replaced)
{
OrderItem replacement = e.ReplacedWith;
Console.WriteLine("{0} (quantity {1}) was replaced " +
"by {2}, (quantity {3}).", item.Description,
item.Quantity, replacement.Description,
replacement.Quantity);
}
else if(e.ChangeType == ChangeType.Cleared)
{
Console.WriteLine("The order list was cleared.");
}
else
{
Console.WriteLine("{0} (quantity {1}) was {2}.",
item.Description, item.Quantity, e.ChangeType);
}
}
}
// This class represents a simple line item in an order. All the
// values are immutable except quantity.
//
public class OrderItem
{
private int _partNumber;
private string _description;
private double _unitPrice;
private int _quantity;
public int PartNumber { get { return _partNumber; }}
public string Description { get { return _description; }}
public double UnitPrice { get { return _unitPrice; }}
public int Quantity { get { return _quantity; }}
public OrderItem(int partNumber, string description, int quantity,
double unitPrice)
{
_partNumber = partNumber;
_description = description;
_quantity = quantity;
_unitPrice = unitPrice;
}
public override string ToString()
{
return String.Format(
"{0,9} {1,6} {2,-12} at {3,8:#,###.00} = {4,10:###,###.00}",
PartNumber, _quantity, Description, UnitPrice,
UnitPrice * _quantity);
}
}
/* This code example produces the following output:
Widget (quantity 400) was Added.
Sprocket (quantity 27) was Added.
Motor (quantity 10) was Added.
Gear (quantity 175) was Added.
110072674 400 Widget at 45.17 = 18,068.00
110072675 27 Sprocket at 5.30 = 143.10
101030411 10 Motor at 237.50 = 2,375.00
110072684 175 Gear at 5.17 = 904.75
Contains(101030411): True
weekly[101030411].Description: Motor
Remove(101030411)
Motor (quantity 10) was Removed.
Insert(2, new OrderItem(...))
Nut (quantity 10) was Added.
coweekly[2].Description: Nut
coweekly[2] = new OrderItem(...)
Nut (quantity 10) was replaced by Crank, (quantity 27).
IndexOf(temp): 2
Remove(temp)
Crank (quantity 27) was Removed.
RemoveAt(0)
Widget (quantity 400) was Removed.
coweekly(1) = New OrderItem(...)
Gear (quantity 175) was replaced by Gear, (quantity 1175).
110072675 27 Sprocket at 5.30 = 143.10
110072684 1175 Gear at 5.17 = 6,074.75
The order list was cleared.
*/
Imports System.Collections.Generic
Imports System.Collections.ObjectModel
' This class derives from KeyedCollection and shows how to override
' the protected ClearItems, InsertItem, RemoveItem, and SetItem
' methods in order to change the behavior of the default Item
' property and the Add, Clear, Insert, and Remove methods. The
' class implements a Changed event, which is raised by all the
' protected methods.
'
' SimpleOrder is a collection of OrderItem objects, and its key
' is the PartNumber field of OrderItem. PartNumber is an Integer,
' so SimpleOrder inherits KeyedCollection(Of Integer, OrderItem).
' (Note that the key of OrderItem cannot be changed; if it could
' be changed, SimpleOrder would have to override ChangeItemKey.)
'
Public Class SimpleOrder
Inherits KeyedCollection(Of Integer, OrderItem)
Public Event Changed As EventHandler(Of SimpleOrderChangedEventArgs)
' This parameterless constructor calls the base class constructor
' that specifies a dictionary threshold of 0, so that the internal
' dictionary is created as soon as an item is added to the
' collection.
'
Public Sub New()
MyBase.New(Nothing, 0)
End Sub
' This is the only method that absolutely must be overridden,
' because without it the KeyedCollection cannot extract the
' keys from the items.
'
Protected Overrides Function GetKeyForItem( _
ByVal item As OrderItem) As Integer
' In this example, the key is the part number.
Return item.PartNumber
End Function
Protected Overrides Sub InsertItem( _
ByVal index As Integer, ByVal newItem As OrderItem)
MyBase.InsertItem(index, newItem)
RaiseEvent Changed(Me, New SimpleOrderChangedEventArgs( _
ChangeType.Added, newItem, Nothing))
End Sub
Protected Overrides Sub SetItem(ByVal index As Integer, _
ByVal newItem As OrderItem)
Dim replaced As OrderItem = Items(index)
MyBase.SetItem(index, newItem)
RaiseEvent Changed(Me, New SimpleOrderChangedEventArgs( _
ChangeType.Replaced, replaced, newItem))
End Sub
Protected Overrides Sub RemoveItem(ByVal index As Integer)
Dim removedItem As OrderItem = Items(index)
MyBase.RemoveItem(index)
RaiseEvent Changed(Me, New SimpleOrderChangedEventArgs( _
ChangeType.Removed, removedItem, Nothing))
End Sub
Protected Overrides Sub ClearItems()
MyBase.ClearItems()
RaiseEvent Changed(Me, New SimpleOrderChangedEventArgs( _
ChangeType.Cleared, Nothing, Nothing))
End Sub
End Class
' Event argument for the Changed event.
'
Public Class SimpleOrderChangedEventArgs
Inherits EventArgs
Private _changedItem As OrderItem
Private _changeType As ChangeType
Private _replacedWith As OrderItem
Public ReadOnly Property ChangedItem As OrderItem
Get
Return _changedItem
End Get
End Property
Public ReadOnly Property ChangeType As ChangeType
Get
Return _changeType
End Get
End Property
Public ReadOnly Property ReplacedWith As OrderItem
Get
Return _replacedWith
End Get
End Property
Public Sub New(ByVal change As ChangeType, ByVal item As OrderItem, _
ByVal replacement As OrderItem)
_changeType = change
_changedItem = item
_replacedWith = replacement
End Sub
End Class
Public Enum ChangeType
Added
Removed
Replaced
Cleared
End Enum
Public Class Demo
Public Shared Sub Main()
Dim weekly As New SimpleOrder()
AddHandler weekly.Changed, AddressOf ChangedHandler
' The Add method, inherited from Collection, takes OrderItem.
'
weekly.Add(New OrderItem(110072674, "Widget", 400, 45.17))
weekly.Add(New OrderItem(110072675, "Sprocket", 27, 5.3))
weekly.Add(New OrderItem(101030411, "Motor", 10, 237.5))
weekly.Add(New OrderItem(110072684, "Gear", 175, 5.17))
Display(weekly)
' The Contains method of KeyedCollection takes TKey.
'
Console.WriteLine(vbLf & "Contains(101030411): {0}", _
weekly.Contains(101030411))
' The default Item property of KeyedCollection takes the key
' type, Integer. The property is read-only.
'
Console.WriteLine(vbLf & "weekly(101030411).Description: {0}", _
weekly(101030411).Description)
' The Remove method of KeyedCollection takes a key.
'
Console.WriteLine(vbLf & "Remove(101030411)")
weekly.Remove(101030411)
' The Insert method, inherited from Collection, takes an
' index and an OrderItem.
'
Console.WriteLine(vbLf & "Insert(2, New OrderItem(...))")
weekly.Insert(2, New OrderItem(111033401, "Nut", 10, .5))
' The default Item property is overloaded. One overload comes
' from KeyedCollection(Of Integer, OrderItem); that overload
' is read-only, and takes Integer because it retrieves by key.
' The other overload comes from Collection(Of OrderItem), the
' base class of KeyedCollection(Of Integer, OrderItem); it
' retrieves by index, so it also takes an Integer. The compiler
' uses the most-derived overload, from KeyedCollection, so the
' only way to access SimpleOrder by index is to cast it to
' Collection(Of OrderItem). Otherwise the index is interpreted
' as a key, and KeyNotFoundException is thrown.
'
Dim coweekly As Collection(Of OrderItem) = weekly
Console.WriteLine(vbLf & "coweekly(2).Description: {0}", _
coweekly(2).Description)
Console.WriteLine(vbLf & "coweekly(2) = New OrderItem(...)")
coweekly(2) = New OrderItem(127700026, "Crank", 27, 5.98)
Dim temp As OrderItem = coweekly(2)
' The IndexOf method, inherited from Collection(Of OrderItem),
' takes an OrderItem instead of a key.
'
Console.WriteLine(vbLf & "IndexOf(temp): {0}", _
weekly.IndexOf(temp))
' The inherited Remove method also takes an OrderItem.
'
Console.WriteLine(vbLf & "Remove(temp)")
weekly.Remove(temp)
Console.WriteLine(vbLf & "RemoveAt(0)")
weekly.RemoveAt(0)
' Increase the quantity for a line item.
Console.WriteLine(vbLf & "coweekly(1) = New OrderItem(...)")
coweekly(1) = New OrderItem(coweekly(1).PartNumber, _
coweekly(1).Description, coweekly(1).Quantity + 1000, _
coweekly(1).UnitPrice)
Display(weekly)
Console.WriteLine()
weekly.Clear()
End Sub
Private Shared Sub Display(ByVal order As SimpleOrder)
Console.WriteLine()
For Each item As OrderItem In order
Console.WriteLine(item)
Next item
End Sub
Private Shared Sub ChangedHandler(ByVal source As Object, _
ByVal e As SimpleOrderChangedEventArgs)
Dim item As OrderItem = e.ChangedItem
If e.ChangeType = ChangeType.Replaced Then
Dim replacement As OrderItem = e.ReplacedWith
Console.WriteLine("{0} (quantity {1}) was replaced " & _
"by {2}, (quantity {3}).", item.Description, _
item.Quantity, replacement.Description, replacement.Quantity)
ElseIf e.ChangeType = ChangeType.Cleared Then
Console.WriteLine("The order list was cleared.")
Else
Console.WriteLine("{0} (quantity {1}) was {2}.", _
item.Description, item.Quantity, e.ChangeType)
End If
End Sub
End Class
' This class represents a simple line item in an order. All the
' values are immutable except quantity.
'
Public Class OrderItem
Private _partNumber As Integer
Private _description As String
Private _unitPrice As Double
Private _quantity As Integer
Public ReadOnly Property PartNumber As Integer
Get
Return _partNumber
End Get
End Property
Public ReadOnly Property Description As String
Get
Return _description
End Get
End Property
Public ReadOnly Property UnitPrice As Double
Get
Return _unitPrice
End Get
End Property
Public ReadOnly Property Quantity() As Integer
Get
Return _quantity
End Get
End Property
Public Sub New(ByVal partNumber As Integer, _
ByVal description As String, _
ByVal quantity As Integer, _
ByVal unitPrice As Double)
_partNumber = partNumber
_description = description
_quantity = quantity
_unitPrice = unitPrice
End Sub
Public Overrides Function ToString() As String
Return String.Format( _
"{0,9} {1,6} {2,-12} at {3,8:#,###.00} = {4,10:###,###.00}", _
PartNumber, _quantity, Description, UnitPrice, _
UnitPrice * _quantity)
End Function
End Class
' This code example produces the following output:
'
'Widget (quantity 400) was Added.
'Sprocket (quantity 27) was Added.
'Motor (quantity 10) was Added.
'Gear (quantity 175) was Added.
'
'110072674 400 Widget at 45.17 = 18,068.00
'110072675 27 Sprocket at 5.30 = 143.10
'101030411 10 Motor at 237.50 = 2,375.00
'110072684 175 Gear at 5.17 = 904.75
'
'Contains(101030411): True
'
'weekly(101030411).Description: Motor
'
'Remove(101030411)
'Motor (quantity 10) was Removed.
'
'Insert(2, New OrderItem(...))
'Nut (quantity 10) was Added.
'
'coweekly(2).Description: Nut
'
'coweekly(2) = New OrderItem(...)
'Nut (quantity 10) was replaced by Crank, (quantity 27).
'
'IndexOf(temp): 2
'
'Remove(temp)
'Crank (quantity 27) was Removed.
'
'RemoveAt(0)
'Widget (quantity 400) was Removed.
'
'coweekly(1) = New OrderItem(...)
'Gear (quantity 175) was replaced by Gear, (quantity 1175).
'
'110072675 27 Sprocket at 5.30 = 143.10
'110072684 1175 Gear at 5.17 = 6,074.75
'
'The order list was cleared.
Example 2
The following code example shows how to override the protected ChangeItemKey method to support mutable keys, and how to override the protected InsertItem, RemoveItem, ClearItems, and SetItem methods to maintain the integrity of the keys and the collection.
The code example creates the MutableKeys collection, which derives from KeyedCollection<TKey,TItem>, and the MutableKey class. The MutableKey class has a settable Key property. When a new key is assigned to the property, the property setter calls the internal (Friend in Visual Basic) ChangeKey method of the collection to test whether the new key would conflict with an existing key. If so, an exception is thrown and the property value is not changed.
In order to maintain the connection between a MutableKey object and the MutableKeys collection and to prevent an object from being inserted into two collections, the MutableKey class has an internal (Friend in Visual Basic) Collection field. This field is maintained by the protected methods that provide custom behavior for adding and removing items from the collection, such as the InsertItem method. The field is set when the item is added to a collection and cleared when the item is removed.
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
// This class demonstrates one way to use the ChangeItemKey
// method to store objects with keys that can be changed. The
// ChangeItemKey method is used to keep the internal lookup
// Dictionary in sync with the keys of the stored objects.
//
// MutableKeys stores MutableKey objects, which have an Integer
// Key property that can be set. Therefore, MutableKeys inherits
// KeyedCollection(Of Integer, MutableKey).
//
public class MutableKeys : KeyedCollection<int, MutableKey>
{
// This parameterless constructor delegates to the base class
// constructor that specifies a dictionary threshold. A
// threshold of 0 means the internal Dictionary is created
// the first time an object is added.
//
public MutableKeys() : base(null, 0) {}
protected override int GetKeyForItem(MutableKey item)
{
// The key is MutableKey.Key.
return item.Key;
}
protected override void InsertItem(int index, MutableKey newItem)
{
if (newItem.Collection != null)
throw new ArgumentException("The item already belongs to a collection.");
base.InsertItem(index, newItem);
newItem.Collection = this;
}
protected override void SetItem(int index, MutableKey newItem)
{
MutableKey replaced = Items[index];
if (newItem.Collection != null)
throw new ArgumentException("The item already belongs to a collection.");
base.SetItem(index, newItem);
newItem.Collection = this;
replaced.Collection = null;
}
protected override void RemoveItem(int index)
{
MutableKey removedItem = Items[index];
base.RemoveItem(index);
removedItem.Collection = null;
}
protected override void ClearItems()
{
foreach( MutableKey mk in Items )
{
mk.Collection = null;
}
base.ClearItems();
}
internal void ChangeKey(MutableKey item, int newKey)
{
base.ChangeItemKey(item, newKey);
}
public void Dump()
{
Console.WriteLine("\nDUMP:");
if (Dictionary == null)
{
Console.WriteLine(" The dictionary has not been created.");
}
else
{
Console.WriteLine(" Dictionary entries");
Console.WriteLine(" ------------------");
foreach( KeyValuePair<int, MutableKey> kvp in Dictionary )
{
Console.WriteLine(" {0} : {1}", kvp.Key, kvp.Value);
}
}
Console.WriteLine("\n List of items");
Console.WriteLine(" -------------");
foreach( MutableKey mk in Items )
{
Console.WriteLine(" {0}", mk);
}
}
}
public class Demo
{
public static void Main()
{
MutableKeys mkeys = new MutableKeys();
// The Add method is inherited from Collection.
//
mkeys.Add(new MutableKey(110072674, "Widget"));
mkeys.Add(new MutableKey(110072675, "Sprocket"));
mkeys.Dump();
Console.WriteLine("\nCreate and insert a new item:");
MutableKey test = new MutableKey(110072684, "Gear");
mkeys.Insert(1, test);
mkeys.Dump();
try
{
Console.WriteLine("\nTry to insert the item again:");
mkeys.Insert(1, test);
}
catch(ArgumentException ex)
{
Console.WriteLine("Error: {0}", ex.Message);
}
Console.WriteLine("\nChange the Key property of the item:");
test.Key = 100000072;
mkeys.Dump();
try
{
Console.WriteLine("\nTry to set the Key property to an existing key:");
test.Key = 110072674;
}
catch(ArgumentException ex)
{
Console.WriteLine("Error: {0}", ex.Message);
}
mkeys.Dump();
}
private static void Display(MutableKeys order)
{
Console.WriteLine();
foreach( MutableKey item in order )
{
Console.WriteLine(item);
}
}
}
// This class has a key that can be changed.
//
public class MutableKey
{
public MutableKey(int newKey, string newValue)
{
_key = newKey;
Value = newValue;
} //New
public string Value;
internal MutableKeys Collection;
private int _key;
public int Key
{
get
{
return _key;
}
set
{
if (Collection != null)
{
Collection.ChangeKey(this, value);
}
_key = value;
}
}
public override string ToString()
{
return String.Format("{0,9} {1}", _key, Value);
}
}
/* This code example produces the following output:
DUMP:
Dictionary entries
------------------
110072674 : 110072674 Widget
110072675 : 110072675 Sprocket
List of items
-------------
110072674 Widget
110072675 Sprocket
Create and insert a new item:
DUMP:
Dictionary entries
------------------
110072674 : 110072674 Widget
110072675 : 110072675 Sprocket
110072684 : 110072684 Gear
List of items
-------------
110072674 Widget
110072684 Gear
110072675 Sprocket
Try to insert the item again:
Error: The item already belongs to a collection.
Change the Key property of the item:
DUMP:
Dictionary entries
------------------
110072674 : 110072674 Widget
110072675 : 110072675 Sprocket
100000072 : 100000072 Gear
List of items
-------------
110072674 Widget
100000072 Gear
110072675 Sprocket
Try to set the Key property to an existing key:
Error: An item with the same key has already been added.
DUMP:
Dictionary entries
------------------
110072674 : 110072674 Widget
110072675 : 110072675 Sprocket
100000072 : 100000072 Gear
List of items
-------------
110072674 Widget
100000072 Gear
110072675 Sprocket
*/
Imports System.Collections.Generic
Imports System.Collections.ObjectModel
' This class demonstrates one way to use the ChangeItemKey
' method to store objects with keys that can be changed. The
' ChangeItemKey method is used to keep the internal lookup
' Dictionary in sync with the keys of the stored objects.
'
' MutableKeys stores MutableKey objects, which have an Integer
' Key property that can be set. Therefore, MutableKeys inherits
' KeyedCollection(Of Integer, MutableKey).
'
Public Class MutableKeys
Inherits KeyedCollection(Of Integer, MutableKey)
' This parameterless constructor delegates to the base class
' constructor that specifies a dictionary threshold. A
' threshold of 0 means the internal Dictionary is created
' the first time an object is added.
'
Public Sub New()
MyBase.New(Nothing, 0)
End Sub
Protected Overrides Function GetKeyForItem( _
ByVal item As MutableKey) As Integer
' The key is MutableKey.Key.
Return item.Key
End Function
Protected Overrides Sub InsertItem( _
ByVal index As Integer, ByVal newItem As MutableKey)
If newItem.Collection IsNot Nothing Then _
Throw New ArgumentException("The item already belongs to a collection.")
MyBase.InsertItem(index, newItem)
newItem.Collection = Me
End Sub
Protected Overrides Sub SetItem(ByVal index As Integer, _
ByVal newItem As MutableKey)
Dim replaced As MutableKey = Items(index)
If newItem.Collection IsNot Nothing Then _
Throw New ArgumentException("The item already belongs to a collection.")
MyBase.SetItem(index, newItem)
newItem.Collection = Me
replaced.Collection = Nothing
End Sub
Protected Overrides Sub RemoveItem(ByVal index As Integer)
Dim removedItem As MutableKey = Items(index)
MyBase.RemoveItem(index)
removedItem.Collection = Nothing
End Sub
Protected Overrides Sub ClearItems()
For Each mk As MutableKey In Items
mk.Collection = Nothing
Next
MyBase.ClearItems()
End Sub
Friend Sub ChangeKey(ByVal item As MutableKey, _
ByVal newKey As Integer)
MyBase.ChangeItemKey(item, newKey)
End Sub
Public Sub Dump()
Console.WriteLine(vbLf & "DUMP:")
If Dictionary Is Nothing Then
Console.WriteLine(" The dictionary has not been created.")
Else
Console.WriteLine(" Dictionary entries")
Console.WriteLine(" ------------------")
For Each kvp As KeyValuePair(Of Integer, MutableKey) In Dictionary
Console.WriteLine(" {0} : {1}", kvp.Key, kvp.Value)
Next
End If
Console.WriteLine(vbLf & " List of items")
Console.WriteLine(" -------------")
For Each mk As MutableKey In Items
Console.WriteLine(" {0}", mk)
Next
End Sub
End Class
Public Class Demo
Public Shared Sub Main()
Dim mkeys As New MutableKeys()
' The Add method is inherited from Collection.
'
mkeys.Add(New MutableKey(110072674, "Widget"))
mkeys.Add(New MutableKey(110072675, "Sprocket"))
mkeys.Dump()
Console.WriteLine(vbLf & "Create and insert a new item:")
Dim test As New MutableKey(110072684, "Gear")
mkeys.Insert(1, test)
mkeys.Dump()
Try
Console.WriteLine(vbLf & "Try to insert the item again:")
mkeys.Insert(1, test)
Catch ex As ArgumentException
Console.WriteLine("Error: {0}", ex.Message)
End Try
Console.WriteLine(vbLf & "Change the Key property of the item:")
test.Key = 100000072
mkeys.Dump()
Try
Console.WriteLine(vbLf & "Try to set the Key property to an existing key:")
test.Key = 110072674
Catch ex As ArgumentException
Console.WriteLine("Error: {0}", ex.Message)
End Try
mkeys.Dump()
End Sub
Private Shared Sub Display(ByVal order As MutableKeys)
Console.WriteLine()
For Each item As MutableKey In order
Console.WriteLine(item)
Next item
End Sub
End Class
' This class has a key that can be changed.
'
Public Class MutableKey
Public Sub New(ByVal newKey As Integer, ByVal newValue As String)
_key = newKey
Value = newValue
End Sub
Public Value As String
Friend Collection As MutableKeys
Private _key As Integer
Public Property Key As Integer
Get
Return _key
End Get
Set
If Collection IsNot Nothing Then
Collection.ChangeKey(Me, value)
End If
_key = value
End Set
End Property
Public Overrides Function ToString() As String
Return String.Format("{0,9} {1}", _key, Value)
End Function
End Class
' This code example produces the following output:
'
'DUMP:
' Dictionary entries
' ------------------
' 110072674 : 110072674 Widget
' 110072675 : 110072675 Sprocket
'
' List of items
' -------------
' 110072674 Widget
' 110072675 Sprocket
'
'Create and insert a new item:
'
'DUMP:
' Dictionary entries
' ------------------
' 110072674 : 110072674 Widget
' 110072675 : 110072675 Sprocket
' 110072684 : 110072684 Gear
'
' List of items
' -------------
' 110072674 Widget
' 110072684 Gear
' 110072675 Sprocket
'
'Try to insert the item again:
'Error: The item already belongs to a collection.
'
'Change the Key property of the item:
'
'DUMP:
' Dictionary entries
' ------------------
' 110072674 : 110072674 Widget
' 110072675 : 110072675 Sprocket
' 100000072 : 100000072 Gear
'
' List of items
' -------------
' 110072674 Widget
' 100000072 Gear
' 110072675 Sprocket
'
'Try to set the Key property to an existing key:
'Error: An item with the same key has already been added.
'
'DUMP:
' Dictionary entries
' ------------------
' 110072674 : 110072674 Widget
' 110072675 : 110072675 Sprocket
' 100000072 : 100000072 Gear
'
' List of items
' -------------
' 110072674 Widget
' 100000072 Gear
' 110072675 Sprocket
Remarks
If there is a lookup dictionary, this method clears it but does not delete it.
If the number of elements has exceeded the dictionary creation threshold and the KeyedCollection<TKey,TItem> is using a lookup dictionary, it will continue to use a lookup dictionary even though the number of elements is again under the threshold.
This method is an O(n) operation, where n is Count.
Notes for Implementers
Override this method to provide customized behavior for the Clear method, inherited from the Collection<T> generic class.
Call the base class implementation of this method to clear the underlying collection and to clear the lookup dictionary.
Applies to
See also
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