Trouble applying MVVM pattern - wpf

Question

i am having some troubles applying the MVVM pattern, for start i am following this example to learn how to apply and use the pattern...
http://msdn.microsoft.com/en-us/magazine/dd419663.aspx
So my problem is establishing the "connection" between the View with the ViewModel...
In the example we have a View with a CollectionViewSource where the Source is the AllCustomers property:
<UserControl
x:Class="DemoApp.View.AllCustomersView"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:scm="clr-namespace:System.ComponentModel;assembly=WindowsBase">
<UserControl.Resources>
<CollectionViewSource x:Key="CustomerGroups" Source="{Binding Path=AllCustomers}"/>
</UserControl.Resources>
<DockPanel>
<ListView AlternationCount="2" DataContext="{StaticResource CustomerGroups}" ItemsSource="{Binding}">
<ListView.View>
<GridView>
<GridViewColumn Header="Name" DisplayMemberBinding="{Binding Path=DisplayName}"/>
<GridViewColumn Header="E-mail" DisplayMemberBinding="{Binding Path=Email}"/>
</GridView>
</ListView.View>
</ListView>
</DockPanel>
</UserControl>
who belongs to the ViewModel AllCustomersViewModel:
public class AllCustomersViewModel : WorkspaceViewModel
{
(...)
public ObservableCollection<CustomerViewModel> AllCustomers { get; private set; }
(...)
}
but he uses a ResourceDictionary where he applies a DataTemplate between the View and the ViewModel:
<DataTemplate DataType="{x:Type vm:AllCustomersViewModel}">
<vw:AllCustomersView />
</DataTemplate>
but my problem is because i am not using a ResourceDictionary, and because of that i thought that i can put the DataTemplate in the Resources of the Window where i will have my View (for me is the more logic place to put the DataTemplate)... But for some reason the Data isn't appearing in the ListView, and so i ask why?

Answer 1

I wouldn't attach the view model in the Xaml. This hard-codes the Xaml to a specific view model.
Instead, I'd override the Application startup:
private void OnStartup(object sender, StartupEventArgs e)
{
Views.MainView view = new Views.MainView();
view.DataContext = new ViewModels.MainViewModel();
view.Show();
}
See this article:
http://www.codeproject.com/KB/WPF/MVVMQuickTutorial.aspx
This approach is also helpful if you use some sort of tool to dynamically bind your view models in the future, like MEF, Castle.Windsor or Prism.

Answer 2

I never bind my view models to my view in XAML. I prefer to have control over when that binding is set myself. I always put a property on the View that contains the reference to the view Model. That way I can change the view model out if needed without any unsuspecting consequences from XAML binding. Plus doing it this way allows me to put an INotify handler on the view model so all changes are updated automatically when the view model is switched.

Answer 3

DataTemplates without key are applied implicitly whereever data of the specified DataType is used as content that is to be displayed. That means that your ViewModel needs to appear somewhere, for example as the content of a ContentControl or an item of an ItemsControl.
So if you have a window you need to have an instance of the ViewModel in it:
<Window ...>
<Window.Resources>
<DataTemplate DataType="{x:Type vm:AllCustomersViewModel}">
<vw:AllCustomersView />
</DataTemplate>
</Window.Resources>
<Window.Content>
<vm:AllCustomersViewModel />
</Window.Content>
</Window>
Normally you only use windows as shells though, and the content is set dynamically.