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Tour of DevForce Silverlight - Part 4

Last modified on November 06, 2012 13:10

Part 4: Tidying up - In Part 4 of this series we'll further refine the work we did in Part 3 to address some infelicities in the user experience and fix a bug or two.

This video was recorded using DevForce 2010. Download the sample code below for updated techniques in DevForce 2012.



Fix UI problems

If you've been following along in this series you've noticed a few user experience issues:  the screen is empty at launch and the form appears to be disabled as you navigate from employee to employee. 

The first problem was solved with a simple fix to our code:  when the Employees collection finished loading asynchronously we weren't setting the CurrentEmployee property and raising a change notification.  

C#
var results = await query.ExecuteAsync();
results.ForEach(Employees.Add);
CurrentEmployee = Employees.FirstOrDefault();

private Employee _currentEmployee;
public Employee CurrentEmployee {
 get { return _currentEmployee; }
 set { _currentEmployee = value; RaisePropertyChanged("CurrentEmployee");}
}
VB
Dim results = Await query.ExecuteAsync()
results.ForEach(Sub(emp) Employees.Add(emp))
CurrentEmployee = Employees.FirstOrDefault

private Employee _currentEmployee
public Employee CurrentEmployee
Get
Return _currentEmployee
End Get
Set
_currentEmployee = value
RaisePropertyChanged("CurrentEmployee")
End Set

The disabled appearance of the DataForm buttons was solved with a bit of a hack. Follow the video and see the downloaded code for how a second busy indicator was added while Employee.Orders are fetched.

It would also be nice to have grid splitters so that the sections of the screen aren't fixed sizes.  Easy with the GridSplitter control:

C#
<sdk:GridSplitter Grid.Row="1" Height="5" HorizontalAlignment="Stretch"
                  VerticalAlignment="Top" ShowsPreview="True"/>

<sdk:GridSplitter Grid.Row="2" Height="5" HorizontalAlignment="Stretch"
                  VerticalAlignment="Top" ShowsPreview="True"/>
VB
<sdk:GridSplitter Grid.Row="1" Height="5" HorizontalAlignment="Stretch"
                  VerticalAlignment="Top" ShowsPreview="True"/>

<sdk:GridSplitter Grid.Row="2" Height="5" HorizontalAlignment="Stretch"
                  VerticalAlignment="Top" ShowsPreview="True"/>

The next usability improvement would be a vertical scroll bar for the logged messages.  Let's do that by swapping the ItemsControl for a ListBox.

C#
<ListBox ItemsSource="{Binding Log}" Grid.Row="2" />
VB
<ListBox ItemsSource="{Binding Log}" Grid.Row="2" />

Fix a latent bug with Add

There's also a bug here with our Add logic.  You may not have run into it yet, but the CollectionChanged add logic is also firing when the Employees collection is first loaded.  We obviously don't need to add the queried employees to the EntityManager, since they're already in the entity cache.  We can fix this by checking the EntityState of the new entity:  if it's detached that tells us the EntityManager doesn't yet know about it and we can safely add it to the manager.

C#
private void Add(System.Collections.Generic.IEnumerable<Employee> employees) {
 if (employees.Any(emp => emp.EntityAspect.EntityState.IsDetached())) {
    _mgr.AddEntities(employees); // simply add to manager in bare state
 }
}
VB
Private Sub Add(ByVal employees As System.Collections.Generic.IEnumerable(Of Employee))
If employees.Any(Function(emp) emp.EntityAspect.EntityState.IsDetached()) Then
_mgr.AddEntities(employees) ' simply add to manager in bare state
End If
End Sub

Learn More

Here are some links for more detail on what we've covered here, and additional information we hope you find useful.

Prerequisites

The user interface for the application built during this tour uses a DataForm component supplied by the Silverlight 5 Toolkit (different from the Silverlight 5 Tools!). You can download the Toolkit here:

http://silverlight.codeplex.com/


Created by DevForce on May 11, 2011 15:57

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