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.