We usually represent our data in a variety of different forms, such as lists, graphics, and more.
We also wish to notify all objects that depend on its object when data changes.
For example: We can use graphics, forms, or list boxes to display stock prices. When the price of stock changes, we expect to change the other parts.
In this case we can use the OBServer mode. We can easily use Observer mode to make our program can easily solve the above problems.
Structural map:
The observer mode assumes that the object of the object and the object of display data are separated, and the objects to display the data objects to observe the changes in the data object. (As shown)
When we want to implement OBServer mode, the data object is usually used as a target, and the object of each display data is used as an Observer. Each Observer is registered in the data he is interested in data by calling a publication in the target (SubiC). Thus, when the data changes, each target transmits an update notification through the Observer interface.
We define two interfaces:
'Observer.vb
'Define Observer interface
Public Interface Observer
Sub sendnotify (Byval Mesg As String) 'is used to send update notifications
End interface
SUBJECT.VB
'Define the Subject interface
Public Interface Subject
Sub Registerinterest (Byval Obs As Observer) 'for registering the observer
End interface
We can write a simple program to better understand the obselver observer mode.. The first form-main form, which has 3 radio button, named Red, Blue and Green.
Our main window is implemented on the Subject interface, which means it must provide public method REGISTEREST for registration (OBSERVER) observer.
Public Sub Registerinterest (Byval Obs As VBServer.observer) IMPLEments VBNETOBSERVER.SUBJECT.REGISTERINTEREST
Observers.Add (OBS)
End Sub
We build two OBServer, a display color, and another color in a list box. We show them in the main window body class.
DIM LSCOL AS New Listobs (ME)
Lscol.show ()
Dim Frcol As New Colframe (ME)
Frcol.show ()
The first observer (OBServer) --------- ColorFrame, it implements the OBServer interface, below is part of the main code.
'Class Colorframe
Public Class Colframe
Inherits System.Windows.Forms.form
Implements Observer 'implements OBServer interface
Private colname as string
DIM FNT AS FONT
DIM BBRUSH As Solidbrush 'Constructor
Public Sub New (Byval Subj As Subject)
Mybase.new ()
Subj.Registerinterest (me) 'Register OBServer
COLFRAME = ME
InitializeComponent ()
FNT = New Font ("Arial", 18, Drawing.FontStyle.Bold)
Bbrush = new solidbrush (color.black)
AddHandler Pic.Paint, New Forms.PainteventHandler (Addressof Painthandler)
End Sub
Public Shadows Sub Dispose ()
Mybase.dispose ()
Components.dispose ()
End Sub
'----
Public Sub SendNotify (Byval Mesg As System.String) IMPLEments VBNETOBSERVER.OBSERVER.SENDNOTIFY
ColName = MESG
Select Case Mesg.Tolower
Case "Red"
Pic.backcolor = color.red '
Case "blue"
Pic.backcolor = color.blue
Case "Green"
Pic.backcolor = color.green
End SELECT
End Sub
END CLASS
Our Listbox form is also an Observer observer that adds colors to the list. Here are some main code.
Public Class Listobs
Inherits System.Windows.Forms.form
Implements Observer
Public Sub New (Byval Subj As Subject)
Mybase.new ()
Listobs = me
InitializeComponent ()
Subj.Registerinterest (ME)
End Sub
'-----
Public Shadows Sub Dispose ()
Mybase.dispose ()
Components.dispose ()
End Sub
'-----
Public Sub SendNotify (Byval Mesg As System.String) IMPLEments Observer.sendnotify
Lscolors.Items.Add (MESG)
End Sub
END CLASS
In our program, click any of the Radio Button in the main form, which will call the SendNotify method of each registered OBServer.
The effect of operation is:
Reference:
Design Patterns: the use of C # Delegate to improve the Observer pattern of: Lu Yan explore the observer design pattern
I just started learning the design mode in .NET, I hope to help everyone in the learning process!
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