In my earlier article title
Using
the .NET Compact Framework, we saw how to use the
Smart Device Extensions project to create an application
that can execute on devices operating on the Pocket PC operating
system. Although the article explained some of the core concepts
about developing for smart devices, an application on the device
becomes useful when it can access data from the enterprise.
For example, if you are developing an application that allows
a sales representative to collect orders during his field visits,
the application will be really useful, when the sales representative
can download the list of products from a web service or upload
the list of sales calls to the central application via a web
service.
In this article, we will see
how to integrate web services with a smart device application.
The process of integration with a web service is very similar
to that of a normal .NET application integrating with a web
service. This shows the true power of the .NET Compact Framework
in providing the same paradigm between various applications
for different platforms.
Calculator Web Service
The web service that we are
going to build for this article is a simple calculator web service.
This service will provide two operations to the user.
A facility to add two numbers.
A facility to subtract two numbers.
Both these web services take
integers as input and return an integer as output. A product
web service will be more complicated and might return more complex
data types (like a DataSet). But this example helps to just
illustrate the concept. Start Visual Studio .NET and create
an ASP.NET web service project (called Calculator). The
following is the code for the web service.
<Webmethod(Description:="Add
operation of the calculator.")> _
Public Function Add(ByVal number1 As Integer, ByVal number2
As Integer) As Integer
' Simply add the two numbers
and return the result back
Return (number1 + number2)
End Function
<Webmethod(Description:="Subract
operation of the calculator.")> _
Public Function Subtract(ByVal number1 As Integer, ByVal
number2 As Integer) As Integer
'
Simply subtract the two numbers and return the result
back
Return
(number1 - number2)
End Function
Note that I've not put in the
designer generated code. Save the code. Its important that we
test the web service so that it functions the way we want. Execute
the project and you should now see the web service description
file as shown in the following figure.
Let us test one operation of
our web service (called Add). To do this, click
on the Add link. You should now see the web
site asking you for two inputs as shown in the following figure.
There is more to the above screen,
but I've just pasted the required output. Now, we can enter
some sample input and then click on the Invoke button.
This will show the output from the web service as shown in the
following figure.
The above diagram shows the
output when you enter an input of 10 and 12.
Ok, now our service is working
fine and we are all set to integrate it with our smart device
application.
Developing the SDE Application
Let's now develop the consumer
for this calculator application. In Visual Studio .NET, select
a new Smart Device Application project. Let's call it CalculatorConsumer
as shown in the following figure.
After you decide on the project
name, Visual Studio presents you with a device profile
screen. A device profile allows you to target a specific smart
device. For our application, we will target a Pocket PC and
develop and Windows application on the same. This is shown in
the following figure.
At this stage Visual Studio
.NET presents the design surface for the project. Before we
start designing our screen, let's create a reference to our
web service. For this, right-click on the Reference
node and choose Add Web Reference. You will
now see the web reference dialog box. In this, enter the URL
to our web service (for example: http://yourComputer/Calculator/Calculator.asmx).
The dialog box will now show the WSDL for the service. Let's
give a name to this service (called CalcService).
This is shown in the following figure.
Click on the Add Reference
button to enable Visual Studio to generate all the proxy classes
for communicating with actual service. Ok, let's design the
form. The following figure shows a simple schematic of the form
that I have designed for the calculator.
The following table shows the
various controls placed in the form and the name that we have
given for the same.
Control Type
Control Name
Control Value
Label
lblOperation
Operation.
Combo Box
cboOperation
Clear the caption
and add two values Add and Subtract.
Label
lblNumber1
Number 1.
Text Box
txtNumber1
Clear the text
value.
Label
lblNumber2
Number 2.
Text Box
txtNumber2
Clear the text
value.
Button
btnCompute
Compute.
Multi-Line Text
Box
txtResult
Clear the text
value.
Form
frmCalculator
Calculator (text
property)
Ok, we have designed the core
of the form. Now, we need to add some code to the Compute
button, which will process the input and display the result.
Here is the code the click event of the Compute
button.
'
Do some basic error handling
If (txtNumber1.Text = "" Or txtNumber2.Text
= "" Or IsNothing(cboOperation.SelectedItem))
Then
MessageBox.Show("Both inputs
and an operation must be provided for the calculator.",
_
"Error",
MessageBoxButtons.OK, MessageBoxIcon.Exclamation, MessageBoxDefaultButton.Button1)
Else
' Create a reference to the web
service
Dim oCalcService As CalcService.Calculator
oCalcService = New CalcService.Calculator
'
Decide the operation to perform based on what was selected
in the
'
combo box
Select
Case cboOperation.SelectedItem.ToString()
Case
"Add"
txtResult.Text
= oCalcService.Add(txtNumber1.Text, txtNumber2.Text)
Case
"Subtract"
txtResult.Text
= oCalcService.Subtract(txtNumber1.Text, txtNumber2.Text)
End
Select
End If
The code is quite simple and
in fact looks very similar to a normal .NET application. We
do some basic error handling and if there are no errors, we
create a reference to the web service and then invoke the Add
or the Subtract method on the service. That's
all there is to it!!! Let's execute the application now. When
you execute the application, Visual Studio presents you with
a dialog box about the deployment options. Since we are going
to deploy to an emulator, choose the emulator option as shown
in the following figure.
After the application is deployed
(along with the .NET Framework), the application is automatically
launched. Before we test the application, it is good to see
if the web service is reachable by the emulator. To do this,
we need to stop the application. For this, you can use the Settings
option and use the RunningPrograms
tab as shown in the following figure.
Click on the Stop
button to stop the selected application. After the application
is stopped (you will also see Visual Studio .NET stop the program,
which is OK), you can open the Internet Explorer application
in the device and type in the URL for your web service. If everything
is fine, you will see the same WSDL description file as shown
in the following figure.
You can now close the Internet
Explorer window and then run the application again, by navigating
to the Program Files folder using the
File Explorer application. When you execute
the application, you see the following output. Play around with
the inputs and check out our basic error handling too!!
When you are done, you can close
the emulator and return back to Visual Studio. For other tips
on how to debug emulator issues, refer to my article here. Well,
that was a whirlwind tour about integrating a web service, but
in real-world applications, you will probably have the web service
connect to a SQL Server and fetch more complex data, but the
principle is the same.
Conclusion
In this article we saw a very
simple example of integrating a web service with a smart device
application. The method is very simple and similar to the way
a normal .NET application integrates with a web service.
