Is this a good way of using ViewModelLocator in MVVM - silverlight

Question

WE have a ViewModelLocater class in our Silverlight App. It consist of a basic constructor and a public property to return the ViewModel for a class. The code is something like this
public class ViewModelLocator
{
private Dictionary<string, ViewModel> _viewModels =
new Dictionary<string, ViewModel>();
public ViewModelLocator()
{
_viewModels.Add("Home", HomeViewModel());
_viewModels.Add("Setup", new SetupViewModel());
_viewModels.Add("TasksActivities", new TasksActivitiesViewModel());
_viewModels.Add("Timesheet", new TimesheetViewModel());
}
public ViewModel this[string viewName]
{
get { return _viewModels[viewName]; }
}
}
and in each of the XAML pages we set the ViewModel for that page using
DataContext="{Binding [Setup], Source={StaticResource ViewModelLocator}}"
Setup is the key in the above dictionary.
The Silverlight App is really big and we have only recently started looking into any memory leaks(There are many...) I am using Windbg to track these leaks and I have noticed a lot of memory leaks leading back to the ViewModelLocater class. Every time the app loads the ViewModelLocator constructor creates ViewModels for all the Views. So I am wondering if there is a better way of implementing the ViewModelLocator class.

Answer 1

We use ViewModelLoader/ViewModelLocator to provide both DesignTime as well as Runtime DataContexts.
ViewModelLocator Class
public static class ViewModelLocator
{
public static readonly DependencyProperty FactoryProperty = DependencyProperty.RegisterAttached("Factory",
typeof (IViewModelFactory), typeof (ViewModelLocator),
new FrameworkPropertyMetadata(null, PropertyChangedCallback));
public static void SetFactory(DependencyObject dependencyObject, IViewModelFactory value)
{
dependencyObject.SetValue(FactoryProperty, value);
}
public static IViewModelFactory GetFactory(DependencyObject dependencyObject)
{
return (IViewModelFactory) dependencyObject.GetValue(FactoryProperty);
}
private static void PropertyChangedCallback(DependencyObject dependencyObject,
DependencyPropertyChangedEventArgs dependencyPropertyChangedEventArgs)
{
var fe = dependencyObject as FrameworkElement;
if (fe != null)
{
fe.DataContext = GetFactory(dependencyObject).Create();
}
}
}
IViewModelFactory
public interface IViewModelFactory
{
object Create();
}
ViewModelFactory
public class MainViewModelFactory : ViewModelFactoryBase
{
protected override object CreateDesignTimeViewModel()
{
return new MainViewModel(new DesignTimeEventAggregator(), new DesignTimeLogger(), new ViewModelViewRepository());
}
protected override object CreateViewModel()
{
return ServiceLocator.Current.GetInstance<MainViewModel>();
}
}
ViewModelFactoryBase Class
public abstract class ViewModelFactoryBase : IViewModelFactory
{
protected abstract object CreateDesignTimeViewModel();
protected abstract object CreateViewModel();
public object Create()
{
return Designer.IsInDesignTime() ? CreateDesignTimeViewModel() : CreateViewModel();
}
}
And in XAML, this is how I hookup ViewModel Locator to View:
<viewModelLocation:ViewModelLocator.Factory>
<viewModelFactories:MainViewModelFactory />
</viewModelLocation:ViewModelLocator.Factory>