Mvvm Light & EventToCommand - Textbox LostFocus firing twice - silverlight

Question

I have a few textboxes on a form that, when focus is lost, I'd like to call a setter stored procedure to save the data, then in my callback function call a getter stored proc which will update a job costing summary on my form. I'm using Mvvm light & when I try & bind an EventToCommand on a LostFocus EventTrigger, my command is fired twice.
I understand this is due to event bubbling, but I'm not sure how to make sure my method is only actually fired once. Here's my xaml:
<TextBox x:Name="txtMiles" Grid.Row="1" Width="80" Grid.Column="2" Margin="2" Text="{Binding Miles, Mode=TwoWay}" HorizontalAlignment="Center" >
<i:Interaction.Triggers>
<i:EventTrigger EventName="LostFocus">
<cmd:EventToCommand Command="{Binding UpdateJobCost}" CommandParameter="{Binding Text, ElementName=txtMiles}"/>
</i:EventTrigger>
</i:Interaction.Triggers>
</TextBox>
And my ViewModel:
public RelayCommand<string> UpdateJobCost { get; set; }
public WorkOrderControlViewModel(TSMVVM.Services.IWorkOrderService workOrderService)
{
WorkOrderService = workOrderService;
RegisterCommands();
LoadData();
}
private void RegisterCommands()
{
UpdateJobCost = new RelayCommand<string>((value) => updateJC(value));
}
private void updateJC(string value)
{
//Handle Setter service call here
}
Many thanks,
Scott

Answer 1

I haven't seen that problem before with EventToCommand. There might be something funky in your app that's causing the problem.
In general I don't rely on the UI to do the right thing. If updateJC shouldn't execute before a previous call has finished, consider adding an "isUpdatingJC" flag in your class. Only update the JC when the flag is false, and set it to true before you get started with the update. That way you don't get in a tight spot because some UI has issues.
Hope that helps...
Cheers!

Answer 2

The problem wasn't with updateJC firing async and not being complete when it fires again. I want it to only fire once. I ended up just creating a class for this form which contained a property for each of the fields. Whenever I update the property, I call updateJC which gathers the object & sends along for processing