On the use of .NET development agency model

When we need to use the object is complex or takes a long time to construct, then you can use proxy mode (Proxy). For example: If you build an object is time consuming and computer resources, the agent mode (Proxy) allows us to control this situation, until we need to use the actual object. The method of a proxy (Proxy) typically comprises the use and the object will be the same, once you start using this object, the method passes to the actual object through a proxy (Proxy).

　　 Some cases can use proxy mode (Proxy) are:

　　 1, an object, such as a large image, you need to load a long time.

　　 2, requires a long time before the results can be done, and it needs to display an intermediate calculation result of the process

　　 3, an object that exists on a remote computer, the remote object needs to be loaded through the network it takes a very long time, especially in the network transmission peak.

　　 4, only a limited access to the object, the proxy mode (Proxy) can verify the user's permission

　　 Agent mode (Proxy) may also be used to distinguish an object instance of the request and the actual access, for example: the program may be established during initialization multiple objects, but not all at once using proxy mode (proxy) to load the real object need.

　　 This is a great need to load and display an image of the program, when the program starts, it must determine the image to be displayed, but the actual image can be displayed only after fully loaded! Then we can use proxy mode (Proxy).

　　 The proxy mode (Proxy) can delay the loading of the actual image, until it receives a request paint. During the loading of the actual image we can use proxy mode (Proxy) in the actual position of the image to be displayed pre-load a relatively small, simple graphics.

　　 Proxy image Code:

Public Class ImageProxy

　 Private done As Boolean
　 Private tm As Timer

　 Public Sub New()
　　 done = False
　　 '设置timer 延迟5秒
　　 tm = New Timer(New TimerCallback(AddressOf tCallback), Me, 5000, 0)
　 End Sub

　 Public Function isReady() As Boolean
　　 Return done
　 End Function

　 Public Function getImage() As Image
　　 Dim img As Imager
　　 '显示预先的图像，直到实际图像载入完成
　　 If isReady Then
　　　 img = New FinalImage()
　　 Else
　　　 img = New QuickImage()
　　 End If

　　 Return img.getImage
　 End Function

　 Public Sub tCallback(ByVal obj As Object)
　　 done = True
　　 tm.Dispose()
　 End Sub
End Class

　　 Define a simple interface:

Public Interface Imager
　 Function getImage() As image
End Interface

　　 Implementing the interface:

　　 an image preloaded classes:

Public Class QuickImage

　 Implements Imager
　 Public Function getImage() As Image Implements Imager.getImage
　　 Return New bitmap("Box.gif")
　 End Function

End Class

　　 The actual image of the class is loaded:

Public Class FinalImage

　 Implements Imager

　 Public Function getImage() As Image Implements Imager.getImage
　　 Return New Bitmap("flowrtree.jpg")
　 End Function

End Class

　　 In the form of a display image, (the Proxy) defining an instance of the proxy image, the button image in the event of loading, loading the image:

Private imgProxy As ImageProxy

　 Public Sub New()

　　 MyBase.New
　　 Form1 = Me
　　 InitializeComponent
　　 imgproxy = New ImageProxy()
　 End Sub

　 Protected Sub btLoad_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btLoad.Click

　 pic.Image = imgProxy.getImage

End Sub

　　总结：

　　这只是一个很简单的例子（例子来自于《c#设计模式》），通过这个例子可以对代理(Proxy)有初步的认识！Adapter模式和代理模式(Proxy)都是在对象间构造一个简单的层。然而，Adapter模式向对象提供一个不同的接口，代理模式(Proxy)为对象提供相同的接口。深圳代孕电13802269370 代孕微13802269370 北京代孕微13802269370

On the use of .NET development agency model

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