Quick MEF + SL4 question
- by Tom Allen
I'm working on an app in the Silverlight 4 RC and i'm taking the oppertunity to learn MEF for handling plugin controls. I've got it working in a pretty basic manor, but it's not exactly tidy and I know there is a better way of importing multiple xap's.
Essentially, in the App.xaml of my host app, I've got the following telling MEF to load my xap's:
AggregateCatalog catalog = new AggregateCatalog();
DeploymentCatalog c1 = new DeploymentCatalog(new Uri("TestPlugInA.xap", UriKind.Relative));
DeploymentCatalog c2 = new DeploymentCatalog(new Uri("TestPlugInB.xap", UriKind.Relative));
catalog.Catalogs.Add(c1);
catalog.Catalogs.Add(c2);
CompositionHost.Initialize(catalog);
c1.DownloadAsync();
c2.DownloadAsync();
I'm sure I'm not using the AggregateCatalog fully here and I need to be able to load any xap's that might be in the directory, not just hardcoding Uri's obviously....
Also, in the MainPage.xaml.cs in the host I have the following collection which MEF puts the plugin's into:
[ImportMany(AllowRecomposition = true)]
public ObservableCollection<IPlugInApp> PlugIns { get; set; }
Again, this works, but I'm pretty sure I'm using ImportMany incorrectly....
Finally, the MainPage.xaml.cs file implements IPartImportsSatisfiedNotification and I have the following for handling the plugin's once loaded:
public void OnImportsSatisfied()
{
sp.Children.Clear();
foreach (IPlugInApp plugIn in PlugIns)
{
if (plugIn != null)
sp.Children.Add(plugIn.GetUserControl());
}
}
This works, but it seems filthy that it runs n times (n being the number of xap's to load). I'm having to call sp.Children.Clear() as if I don't, when loading the 2 plugin's, my stack panel is populated as follows:
TestPlugIn A
TestPlugIn A
TestPlugIn B
I'm clearly missing something here. Can anyone point out what I should be doing?
Thanks!
