Question

I have a web form that once filled out needs to kick off a lengthy process. Since I don’t want the user sitting there waiting for it to complete, I want to kick off the task and then take the user to another page to continue working.

Would doing this involve using an asynchronus process, and if so, does someone have an example of how to do this?

Answer 1

Basically you need a fire-n-forget implementation where you can just fire an async operation without waiting for it to finish.

Check out the following answer on a related question.

The code is in C#.Net, but vb.net should be similar.

Edit: Vb.net Solution:

This is the vb.net solution to fire a web method asynchronously:

Consider your web method as follows:

Public Class Service1
    Inherits System.Web.Services.WebService

    <WebMethod()> _
    Public Sub LengthyProcess()
        'Perform the lengthy operation
        'Also note this doesn't return anything
        'Hence can be used safely in fire-n-forget way of asynchronous delegate
        System.Threading.Thread.Sleep(1000)
        System.IO.File.WriteAllText("C:\\MyFile.txt", "This is the content to write!", Encoding.UTF8)
        System.Threading.Thread.Sleep(1000)
    End Sub

End Class

Now to call the web method asynchronously you can do either of the following depending your version of .Net:

.Net 3.5 (I am not sure if it works in 2.0)

Make sure to set Async=”true” in your Page directive

<%@ Page Language="vb" AutoEventWireup="false" CodeBehind="Default.aspx.vb" Inherits="WebApplication1._Default" Async="true" %>

And in the code behind:

Partial Public Class _Default
    Inherits System.Web.UI.Page

    Dim webService As MyService.Service1

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    End Sub

    Protected Sub Button1_Click(ByVal sender As Object, ByVal e As EventArgs) Handles Button1.Click
        webService = New MyService.Service1()
        webService.LengthyProcessAsync()
    End Sub

End Class

.Net 2.0/ 1.0

No need to set Async=”true”

And in the code-behind:

Partial Public Class _Default
    Inherits System.Web.UI.Page

    Public Delegate Sub MyDelegateCallBack()
    Dim webService As MyService.Service1

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    End Sub

    Protected Sub Button1_Click(ByVal sender As Object, ByVal e As EventArgs) Handles Button2.Click
        webService = New MyService.Service1()
        Dim del As MyDelegateCallBack
        del = New MyDelegateCallBack(AddressOf webService.LengthyProcess)
        del.BeginInvoke(Nothing, Nothing)
    End Sub
End Class