Tour of DevForce Silverlight - Part 3

Part 3: Extend the entity and show when DevForce is busy - In Part 3 of this series we'll refine the work we did in Part 2:  we'll extend the Employee class with custom business logic and add a busy indicator to show when the application is busy.

• Platform: Silverlight
• Language: C#, VB
• Download: Tour of DevForce Silverlight

Tip  For best results, code along with the step-by-step video. 

Track the CurrentItem

Perhaps when we are fetching orders, we'd also like to know the id of the associated employee.

First, let's add a new member to our view model:

We'll use this to keep track of which employee we are currently viewing the details for.

Next, we'll create an overload of our WriteToLog method that specifically handles queries.

(Recall that the first overload of WriteToLog() that we wrote, shown below, simply takes a string parameter.)

We'll also modify the handler for the Fetching event to use the new overload:

Finally, we need to keep our new CurrentEmployee in sync with the view. We can easily do this using data binding.

Open MainPage.xaml and add the following attribute to the data form:

We can run the application now and see the results of our improved logging.

Extend entities

It would be a nice improvement to show the full name of the employee in the log and not just the id. Currently, we have a FirstName and a LastName, but no FullName property. We could simply concatenate the names when we create the log message, but this is an excellent excuse to show how easily we can extend our entities with custom properties and logic.

Right-click on the SimpleStepsWeb project, and select Add | Class and name it Employee. Modify the new class so that it matches the following:

Notice that we are using the partial keyword. This is because DevForce has already created an Employee class for us and we want to extend that existing class.

Note that the fully qualified name of the class must be the same in all of the files that constitute the partial class. In our case, the fully qualified name is SimpleSteps.Employee.

There is one additional step in order to make our extension of the Employee class visible the Silverlight project. Right-click on the Shared Code folder in SimpleSteps and select Add | Existing Item….

Locate the Employee.cs file that we just created in the SimpleStepsWeb folder. While it is selected in the dialog, click the little drop down on the right side of the Add button and choose Add As Link.

Now Employee.cs is linked with the Silverlight project, just like NorthwindIB.IB.Designer.cs. Before we can compile the class in Silverlight though, we'll also need to remove:

Now we can modify our WriteToLog method in MainPageViewModel to include the employee's full name:

Show busy

We've already pointed out the asynchronous nature of queries against the database from Silverlight.  While the EntityManager is off fetching data we want to take control of the screen to tell the user the application is busy.

We'll make use of the BusyIndicator control from the Silverlight Toolkit to do this. Right-click on SimpleSteps and select Add Reference… and select System.Windows.Controls.Toolkit and click Ok.

Open MainPage.xaml and on the root element add another namespace alias:

We're going to add the busy indicator as the child element of the UserControl. The current child, LayoutRoot, will become the child of the busy indicator. The new structure of the XAML file will look like this:

When the IsBusy property is set to true on the busy indicator, it will overlay the contents of BusyContent, along with an animation, over the regular content.

We've already added a binding to the busy indicator, but there is no corresponding IsBusy property on the view model. Let's add that now. In doing so, we'll also need to implement the INotifyPropertyChanged interface on our view model. This interface allows the data binding system in Silverlight to respond appropriately when the values of bound properties are changed.

Open MainPageViewModel and add a new using statement:

Modify the first line of the class:

Then add these members to the class:

We want to set IsBusy to true whenever we initiate a query and then set it to false whenever the results are returned. Inside the constructor, let's modify our event handlers:

Run the application now and navigate through a couple of employees. You'll see the busy indicator in action.

Simple validation

One more thing to note, and not covered in the video, is the basic validation you get out of the box with DevForce.  In generating your entity model, DevForce examined the schema for basic rules, such as a field not allowing nulls or having a maximum length.  DevForce in turn generated validation attributes on these properties; so for example the LastName here is both required, and has a maximum length of 30 characters.  

We can see this in action if we add a new employee using the DataForm and leave the LastName blank:

Learn More

We've briefly covered a lot of topics here.  Here are some links to what we've covered, and additional information we hope you find useful.

• EntityManager Overview
• The query life cycle
• Adding business logic
• Asynchronous queries and saves 
• DevForce entities and the UI
• Validation overview
• More Silverlight resources
• Silverlight control samples
  
  

Prerequisites

The user interface for the application built during this tour uses a DataForm component supplied by the Silverlight 4 Toolkit (different from the Silverlight 4 Tools!). You can download the Toolkit here:

http://silverlight.codeplex.com/

To work with this application, as all DevForce 2010 Silverlight applications, you will need Visual Studio 2010, the Silverlight 4 runtime (SilverlightTools.exe), and DevForce installed.