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Now you should see com.devbuzz.www
in your project list:
Consuming the web service reference
to the application
Now we come to the fun stuff - consuming
the web service from you Pocket PC. It's pretty interesting
when you look at consuming web services with an eye on performance
- consuming any complex data type is a) very very slow and
b) means that you are restricting your potential consumers
to only those that are using a Windows platform, so XML
is really the only way to go from both a standards and performance
perspective. The first time you call a web service from
the Compact Framework there seems to be a real performance
issue; second and subsequent calls are much faster (I'm
not caching the web service output). I'm using an
XScale iPAQ for this tutorial and I recorded this
video clip (242 kb) as an example of the performance.
As you can see after the first call
the subsequent calls are very fast.
The Code - Option 1
Let's look at the code that executes
when you hit the Go button. This is how we consume the web
service using the proxy class generated by adding the web
reference:
'download the XML from the web service
If txtEmailAddress.Text.Length < 1 Then
btnGetArticles.Enabled = False
UIHelper.statusBarMsg(sbar, "Please enter an email
address.")
Exit Sub
End If
'clear the textbox
TextBox1.Text = ""
Me.Refresh()
UIHelper.ShowWaitCursor(True)
'we want to time this
Dim objTime As New TimeIt
UIHelper.statusBarMsg(sbar, "Retrieving data from web
service.")
objTime.Start()
Dim cnt As Integer
Dim nodeList As XmlNodeList
Dim xNode As XmlNode
Dim rootNode As XmlNode
Dim ws As New com.devbuzz.www.WebAPI
rootNode = ws.GetAuthorArticles(txtEmailAddress.Text)
objTime.Finish()
Dim strServPlusWriteTime As String = objTime.Elapsed.ToString
UIHelper.statusBarMsg(sbar, "Received data - loading
XML.")
If rootNode.HasChildNodes() Then
nodeList = rootNode.ChildNodes
Dim sb As New StringBuilder
For cnt = 0 To nodeList.Count - 1
xNode = rootNode.ChildNodes(cnt)
sb.Append("Title: ")
sb.Append(xNode.Attributes("Title").Value)
sb.Append(ControlChars.CrLf)
sb.Append(UIHelper.showShortDate(xNode.Attributes("Date").Value))
sb.Append(ControlChars.CrLf)
sb.Append("Read: ")
sb.Append(xNode.Attributes("ReadCounter").Value)
sb.Append(ControlChars.CrLf)
sb.Append(xNode.Attributes("DeskTopURL").Value)
sb.Append(ControlChars.CrLf)
sb.Append(ControlChars.CrLf)
Next
TextBox1.Text = sb.ToString
sb = Nothing
End If
UIHelper.statusBarMsg(sbar, "Web
service retrieval: " & _
strServPlusWriteTime)
UIHelper.ShowWaitCursor(False)
The Code - Option 2
Using a Web Request to consume the web
service requires the following code to execute when you
hit the Go button. Note you do not need to add a Web Reference
to use the web service in this fashion:
objTime.Start()
Dim strURL As String = baseWebServiceURI & _
"/class/WebAPI.asmx/GetAuthorArticles?thisEmailAddress="
& _
txtEmailAddress.Text
Dim webReq As HttpWebRequest = WebRequest.Create(strURL)
Dim webRes As HttpWebResponse = webReq.GetResponse
Dim cnt As Integer
Dim dom As New XmlDocument
Dim nodeList As XmlNodeList
Dim xNode As XmlNode
dom.Load(webRes.GetResponseStream)
webReq.Abort()
webRes.Close()
objTime.Finish()
First we concatenate the web service
URL and method name to form a URI:
Dim strURL As String = baseWebServiceURI
& _
"/class/WebAPI.asmx/GetAuthorArticles?thisEmailAddress="
& _
txtEmailAddress.Text
Next we create a HttpWebRequest
using the URI in strURL:
Dim webReq As HttpWebRequest = WebRequest.Create(strURL)
and then call the GetResponse
method to return a HttpWebResponse instance containing
the response from the web service.
Dim webRes As HttpWebResponse = webReq.GetResponse
If you'll recall this web service is
returning an XMLDocument so we can instantiate an
XML document and load the XML response stream using the
XMLDocument.Load method.
dom.Load(webRes.GetResponseStream)
If you're wondering what the webReq.Abort
is doing in there - join the club. We shouldn't need it
but without it after a few calls the web service hangs (thanks
to Neil Cowburn for discovering this when he provided the
code
to check for an internet connection).
Parsing the XML
Dim rootNode As XmlNode
rootNode = dom.DocumentElement
If rootNode.HasChildNodes() Then
nodeList = rootNode.ChildNodes
Dim sb As New StringBuilder
For cnt = 0 To nodeList.Count - 1
xNode = rootNode.ChildNodes(cnt)
sb.Append("Title: ")
sb.Append(xNode.Attributes("Title").Value)
sb.Append(ControlChars.CrLf)
sb.Append(UIHelper.showShortDate(xNode.Attributes("Date").Value))
sb.Append(ControlChars.CrLf)
sb.Append("Read: ")
sb.Append(xNode.Attributes("ReadCounter").Value)
sb.Append(ControlChars.CrLf)
sb.Append(xNode.Attributes("DeskTopURL").Value)
sb.Append(ControlChars.CrLf)
sb.Append(ControlChars.CrLf)
Next
TextBox1.Text = sb.ToString
sb = Nothing
dom = Nothing
End If
Parsing the XML couldn't be any easier
as you can see by the code above. So there you have it.
You can download the code
here - this includes both the proxy and web request
based code outlined above - but remember that this was built
using beta 2 - you should be able to adapt it to beta 1
barring any platform (read XScale) XML and/or web service
issues.
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