Henry Interse - Using Template Method Design Mode
.NET event processing mechanism (2)
By Kevin McFarlane
Han Rui translation (2002.10.14)
4. Example - Template Method Design Mode Event Processing
The following is an example of a complete use of C # and Visual Basic.net. It consists of three classes: Supplier, ExternalClient, and InternalClient. Supplier triggers event. The other two classes perform this event. INTERNALCLIENT is derived from Supplier.
ExternalClient includes an embedded SuppliR reference. However, it is initialized by an InternalClient reference. Therefore, when the ExternalClient is registered for the Supplier event, it calls an onNameChangeD () of INTERNALCLIENT. The event is then processed by the INTERNALCLIENT's NameChanged (), and finally by the nameclient's NameChanged ().
The output of the code is: InternalClient.onnameChanged
INTERNALCLIENT.NAMECHANGED
ExternalClient.nameChanged 1) C # example:
Using system;
Class test
{
Static void main (string [] args)
{
EXTERNALCLIENT Client = New ExternalClient ();
Client.testsupplier ();
}
}
// When its attribute is set, an event is generated
Public Class Supplier
{
Public Supplier () {}
Public Event EventHandler NameChanged;
Public String Name
{
Get {return name;}
Set {name = value; internaMechanged ();
}
// Internal user, that is, derived class, can rewrite the default behavior
protected virtual void onnamechanged ()
{
/ / Execute the default behavior here
Console.writeline ("Supplier.onNameChanged");
}
// If the internal user (derived class) renovates the default behavior in the onNameChanged, the external user will still accept this event.
Private voidinnamechanged ()
{
// Derived class rewritten default behavior
ONNAMECHANGED ();
// After registration, the user can trigger this event.
IF (NameChanged! = null)
NameChanged (this, new evenetargs ());
}
PRIVATE STRING NAME;
}
// "Internal" user handling the support of the Supplier.nameChanged event, but first to rewrite its default behavior
Public Class InternalClient: Supplier
{
PublicinalClient ()
{
NameChanged = New EventHandler (this.supplier_namechanged);
}
protected override void onnamechanged ()
{
// Rewote the default behavior of Supplier.NameChanged
Console.writeline ("InternalClient.onNameChanged");
Private Void Supplier_NameChanged (Object Sender, Eventargs E)
{
// Handle Supplier.nameChanged
Console.writeline ("INTERNALCLIENT.NAMECHANGED");
}
}
// A "external" user that handles the Supplier.nameChanged event.
Public Class ExternalClient
{
Public externalclient ()
{
// Instantate the Supplier as a reference to an InternalClient instance. When an event is evoked, it triggers the overwritten INTERNALCLIENT.ONNAMECHANGED
Supplier = new internelclient ();
Supplier.namechanged = new eventhandler (this.supplier_namechange);
}
Public void testsupplier ()
{
// The following code triggers an event and processes the Handlers of INTERNALCLIENT and EXTERNALCLIENT.
Supplier.name = "kevin mcfarlane";
}
Private Void Supplier_NameChanged (Object Sender, Eventargs E)
{
// Handle Supplier.nameChanged
Console.writeline ("externalClient.namechange);
}
Private Supplier Supplier;
}
2) VB.NET example:
Module Test
Sub main () 'program entry
DIM Client As ExternalClient = New ExternalClient ()
Client.testsupplier ()
End Sub
End module
'When it is set, an event is generated
Public Class Supplier
Sub new ()
End Sub
Public Event NameChanged As EventHandler
Public property name () AS STRING
Get
Return Mname
END GET
Set (byval value as string)
mname = value
INTERNALONNAMECHANGED ()
End set
End Property
'The internal user, that is, derived class, can rewrite the default behavior
Protected overridable sub ?onnamechanged ()
'Execute the default behavior here
Console.writeline ("Supplier.onNameChanged")
End Sub
Private subinloadNameChanged ()
'Derived class rewritten default behavior
ONNAMECHANGED ()
'Evil events for users
RaiseEvent NameChanged (ME, New EventArgs ())
End Sub
Private mname as string
END CLASS
'"Internal" user handling the support of the support of the support, but first to rewrite its default behavior
Public Class InternalClient
Inherits Supplier
Sub new ()
End Sub
Protected overrides sub onnamechanged ()
'Rewrive the default behavior of support support for Supplier.NameChange
Console.writeline ("InternalClient.onNameChanged")
End Sub
Private subsupplier_namechanged (byval e AS Object, ByVal e as Eventargs) _ handles mybase.namechanged
'Hands Supplier.NameChanged
Console.writeline ("InternalClient.nameChanged")
End Sub
END CLASS
'A "external" user that handles the Supplier.NameChanged event.
Public Class ExternalClient
Sub new ()
'Instantilize Supplier as a reference to an INTERNALCLIENT instance. When an event is evoked, it triggers the overwritten INTERNALCLIENT.ONNAMECHANGED
Msupplier = new internelclient ()
'Register for Supplier.nameChanged events
AddHandler Msupplier.nameChanged, Addressof Msupplier_NameChanged
End Sub
Public Sub TestSupplier ()
'The following code triggers an event and processes the Handlers of INTERNALCLIENT and ExternalClient.
Msupplier.name = "kevin mcfarlane"
End Sub
Private sub msupplier_namechanged (Byval e AS Object, ByVal E as Eventargs)
'Hands Supplier.NameChanged
Console.writeline ("externalClient.namechange)
End Sub
Private Msupplier as Supplier
END CLASS
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