Ajax command parsing
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  1. #1
    Join Date
    Sep 2004
    Posts
    65

    Ajax command parsing

    Hi,

    I am creating a web app with VB.NET 1.1 using AJAX. I was wondering if there is a better way to handle events than what I am doing, without downloading an ajax framework.

    My method:
    Each button on web form calls javascript that creates an xml fragment and posts it to a class that handles ajax requests for the page.
    XML:
    Code:
    <AjaxRequest>
         <Command>Foo</Command>
         <Params>
              <Param name="param1">Bar</Param>
              <Param name="param2">Again</Param>
         </Params>
    </AjaxRequest>
    The code on the server pulls out the command field and runs it through a select case to determine which function to call.

    Code:
    Imports System.Web
    Imports System.Xml
    
    Public Class Ajax
        Implements IHttpHandler
    
        Public ReadOnly Property IsReusable() As Boolean Implements System.Web.IHttpHandler.IsReusable
            Get
                Return True
            End Get
        End Property
    
        'Here is where the action is...
        Public Sub ProcessRequest(ByVal context As System.Web.HttpContext) Implements System.Web.IHttpHandler.ProcessRequest
            Dim xmlDoc As XmlDocument
    
            'If the XML document was submitted via post method, then load it in the DOM document
            If (context.Request.InputStream.Length > 0 And context.Request.ContentType.ToString().IndexOf("/xml") > 0) Then
                xmlDoc = New XmlDocument
                xmlDoc.Load(context.Request.InputStream)
    
                Select Case xmlDoc.GetElementsByTagName("Command").Item(0).InnerText
                    Case "Bar"
                        Call Bar()
                    Case "Func2"
                        Call Func2()
                    Case "HelloWorld"
                        Call HelloWorld()
                        ...etc...
                End Select
    
            End If
        End Sub
    
        Public Sub Bar()
            'Get params, do some work, and return something in the Response...
        End Sub
    End Class
    Instead of this select case, are there better methods? It just seems like there should be...

    Thanks,

    Ranthalion

  2. #2
    Join Date
    Apr 2005
    Location
    Norway
    Posts
    3,934

    Re: Ajax command parsing

    Quote Originally Posted by Ranthalion
    Instead of this select case, are there better methods? It just seems like there should be...
    You could use some kind of map (key/value collection) between a specific string (the command) and a delegate (the function to call). Then instead of the select-case stament you simply grab the command from the xml, then lookup the correspoing delegate in the map, and then call the delegate.

    And AFAIK it would be cleaner to use XPath to lookup the command instead of GetElementsByTagName.

    - petter

  3. #3
    Join Date
    Sep 2004
    Posts
    65

    Re: Ajax command parsing

    Thanks. The map seems like it would be pretty much the same thing as the Select Case implementation. Whenever I add a new function, I would have to manually update the map to contain the new command string and function name. I'll think about it some more, though.

    I'm not familiar with XPath yet, so I'll definately check that out. This is the first project that uses xml. Thanks again!

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