Analysis on the use of proxy mode in. NET Development)

When the objects we need to use are complex or need to be constructed for a long time, we can use the Proxy mode ). For example, if building an object takes a lot of time and computer resources, the Proxy mode allows us to control this situation until we need to use the actual object. A Proxy usually contains the same method as the object to be used. Once this object is used, these methods will be passed to the actual object through Proxy.

Some situations where Proxy can be used:

1. An object, such as a large image, needs to be loaded for a long time.

2. A calculation result that takes a long time to complete, and the intermediate result must be displayed during the calculation process.

3. It takes a long time to load a remote object on a remote computer, especially during peak network transmission.

4. An object has only limited access permissions. The Proxy mode can verify the user's permissions.

Proxy mode can also be used to differentiate the request and actual access of an object instance. For example, multiple objects can be created during program initialization, but not all objects can be used immediately, proxy mode can load the desired real object.

This is a program that needs to load and display a large image. When the program starts, you must determine the image to be displayed, however, the actual image can only be displayed after it is fully loaded! Then we can use Proxy ).

This Proxy mode can delay loading of the actual image until it receives a painting request. During actual image loading, We can pre-load a small, simple image at the position where the actual image is to be displayed through the Proxy mode.

Image Proxy code:

Public Class ImageProxy Private done As Boolean Private tm As Timer Public Sub New () Done = False 'Sets the timer Latency by 5 seconds. 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 'Display the pre-image until the actual image is loaded 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

Implementation interface:

Pre-loaded image class:

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

Classes for loading actual images:

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 the displayed image, define an image Proxy instance and load the image in the image button event:

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