Introduction
When using Silverlight, everything is asynchronous. It seems to be the trend, the same goes for Windows 8. This means that you will need to inform the user about progress in the background.
Silverlight uses the BusyIndicator for this behavior. Using MVVM, it might be a bit harder to implement the BusyIndicator in a correct way, but Catel provides the IPleaseWaitService for years which can be mocked easily during test scenarios.
However, it didn’t support a busy indicator per view yet. This fact has changed today, as you can see in the screenshot below:
A long requested feature in Catel was the support for tags in the ServiceLocator. The ServiceLocator is the IoC solution that Catel provides by default. A customer of Catel recently required the busy indicators to show up per view. I thought a bit about it and this could be solved by the recently (read: this week) introduction of the tags in the ServiceLocator.
Setting up the views
The view is responsible for registering the service. This can easily be done using the Catel user controls. Create a view like you always do, then use the following code-behind:
1: protected override void OnViewModelChanged()
2: {
3: var serviceLocator = ServiceLocator.Default;
4:
5: var viewModel = ViewModel;
6: if (viewModel != null)
7: {
8: serviceLocator.RegisterInstance(typeof (IPleaseWaitService), new PleaseWaitService(this), viewModel);
9: }
10: }
This code will be executed when the ViewModel property of the control changes. The view registers a view specific instance of the PleaseWaitService service in the ServiceLocator. It uses the new view model as tag so that will be used to distinguish the services.
Setting up the view models
The view model can retrieve the PleaseWaitService very easily because the tag is itself. To show the view specific please wait service, use this code:
1: var pleaseWaitService = GetService<IPleaseWaitService>(this);
2: pleaseWaitService.Show();
To hide the window again, use this code:
1: var pleaseWaitService = GetService<IPleaseWaitService>(this);
2: pleaseWaitService.Hide();
Customizing the PleaseWaitService
Customizing the please wait service is very, very easy. Just override the class like this:
1: public class MyCustomPleaseWaitService : PleaseWaitService
2: {
3: protected override FrameworkElement CreateBusyIndicator()
4: {
5: var busyIndicator = new MyBusyIndicatorControl();
6:
7: busyIndicator.SetBinding(System.Windows.Controls.BusyIndicator.BusyContentProperty, new Binding("Status"));
8: busyIndicator.SetBinding(System.Windows.Controls.BusyIndicator.IsBusyProperty, new Binding("IsBusy"));
9:
10: return busyIndicator();
11: }
12: }
The base implementation will automatically take care that the data context is updated and that the control is centered as required.