作者：未知 来源：月光软件站 加入时间：2005-2-28　月光软件站

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。

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