在上例子中传递的信息是一个字符串，当我们点击其中一个radio button，我们可以得到这个radio button的名称（Red Blue Green），将这个名称发送到观察者（Observer）。
Observer提供一个对目标主体（Subject）抽象连接，一个目标主体（Subject）不知道他的观察者（Observer）的任何信息，但是当他改变时可以更新通知发送到各个注册过的观察者（Observer）。
我们也可以使用委托（Delegate）来实现Observer模式
Public Class Subject
'定义委托
Public Delegate Sub SendMessageDelegate(ByVal aPrice As String)
'定义事件
Public Event SendMessage As SendMessageDelegate
Dim _askprice As String
Public WriteOnly Property Message() As String
Set(ByVal Value As String)
_askprice = Value
'引发事件
RaiseEvent SendMessage(_askprice)
End Set
End Property
End Class
在主窗体中：
Dim lscol As New listObs
Dim frcol As New frmD
Public Sub New()
MyBase.New()
Form1 = Me
InitializeComponent()
Dim evh As EventHandler = New EventHandler(AddressOf RadioHandler)
AddHandler opRed.Click, evh
AddHandler opBlue.Click, evh
AddHandler opGreen.Click, evh
lscol.Show() ‘显示两个Observer
frcol.Show()
End Sub
‘处理Radio Button的单击事件
Protected Sub RadioHandler(ByVal sender As Object, ByVal e As EventArgs)
Dim i As Integer
Dim rbut As Windows.Forms.RadioButton = CType(sender, Windows.Forms.RadioButton)
Dim subject As New subject
Dim aDelegate As subject.SendMessageDelegate = New subject.SendMessageDelegate(AddressOf lscol.Add)
Dim aDelegate1 As subject.SendMessageDelegate = New subject.SendMessageDelegate(AddressOf frcol.DrawMessage)
‘布线
AddHandler subject.SendMessage, aDelegate
AddHandler subject.SendMessage, aDelegate1
'AddHandler subject.SendMessage, AddressOf lscol.Add
'AddHandler subject.SendMessage, AddressOf frcol.DrawMessage
subject.Message = rbut.Text
‘撤销布线
RemoveHandler subject.SendMessage, aDelegate
RemoveHandler subject.SendMessage, aDelegate1
End Sub
在listbox窗体和ColorFrame窗体分别定义委托所指向的事件：
‘listbox窗体
Public Sub Add(ByVal mesg As System.String)
lsColors.Items.Add(mesg)
End Sub
‘ColorFrame窗体
Public Sub DrawMessage(ByVal mesg As System.String)
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
这样也可以实现相同的效果。
参考资料：
设计模式：利用C#的Delegate来改进Observer模式 作者：卢彦
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