Posted by beakersoft | Posted in Programming | Posted on 07-10-2008
First off, i apologise for not blogging for a while, ive had quite a few other projects on over the summer, plus holidays so I’ve not really had time. Hopefully now I should be able to get back into it with a bit more frequency.
Anyway on to the topic of this post. Most applications nowadays will automaticly go onto the web and check to see if there is a new version, and if there is offer to download/install/visit page etc. I was looking for a simple way to do this using the dotnet framework and Visual Basic.Net, and came across the System.Net class.
This class is extremely powerful, as it contains functions for network communication. The main one we will use here is the System.net.WebClient. We are going to use this to pull a file down of our web server that will give us information about the latest version of our application.
So first of all, create a text file, we are going to look on our web server for this file and read information. In the file we will have the following info: App name, version and download location, delimited by a pipe (|) character. You could also add extra things like new features, release date etc to this file. The example file will look something like this.
Once you have this file, save it as something like TestApp_Ver_Control.txt, and upload it to your web server.
Downloading the Version information
Now the file containing version information is on your web server, we can write a function in vb that will open the file up, get the information contained in it and use that information to decided if our application is the latest version or not. This is where the System.net.WebClient comes in. First of declare a couple of variables. One is the WebClient, one is the url of the file you have just uploaded and a string array to hold the details of the file.
Dim myWebClient As New Net.WebClient Dim RemoteUri As String = "www.beakersoft.co.uk/TestApp_Ver_Control.txt" Dim strFileInfo()As String
Now, we can go and get the file of the web server, using the webclient and read the contents into a string. Then we can split the content of the string up using the pipe char, and there you have all the info you need to check the version.
All the code is wrapped up in a try/catch block to make sure we dont get any unhandled errors such as when there is no net connection, file missing etc.
Try Dim file As New System.IO.StreamReader( _ myWebClient.OpenRead(RemoteUri)) Dim Contents As String = file.ReadToEnd() 'Split up the sections of the text based on the pipe (|) delimiator strFileInfo = Split(Contents, "|") 'see if we need a new version If strFileInfo(0) > Application.ProductVersion Then 'if we have a new version, make sure the app name matchs from the file If strFileInfo(1) = application.ProductName Then 'we have a new version! So throw up a message, set a flag ect End If End If 'close the file stream and web client myWebClient = Nothing file.Close() Catch ex As Exception If InStr(ex.Message, "(404)") Then '404 means file not found on webserver Msgbox("Problem Finding the update information file - " & vbNewLine & ex.Message & _ vbNewLine & "Please contact the appliaction vendor") Else Msgbox("Problem getting update information - " & vbNewLine & ex.Message & _ vbNewLine & "Check your internet settings and try again") End If End Try
And thats pritty much it! This is a very bare bones way of doing it, and you probably want to add in support for using a proxy (you can do that using the System.Net.WebRequest.DefaultWebProxy class, and pass login credentials to myWebClient.Credentials using Net.NetworkCredential ) but as a very basic form this should work.