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How to hook up a ViewModel to a window using an attached property

, 22 Nov 2010 CPOL
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Shows you how you can attach a viewmodel to your WPF window using attached properties, rather than setting the DataContext to a static resource or in code-behind
In my WPF-based projects, I have played around with many methods for setting the DataContext on my shell window, and the latest incarnation of this uses an attached DependencyProperty.
 
Keep in mind, this is experimental code on my part..
 
First, we need to define our attached property:
public static class Application
{
    public static Type GetController(DependencyObject obj)
    {
        return (Type)obj.GetValue(ControllerProperty);
    }
    public static void SetController(DependencyObject obj, Type value)
    {
        obj.SetValue(ControllerProperty, value);
    }
    public static readonly DependencyProperty ControllerProperty =
            DependencyProperty.RegisterAttached("Controller", typeof(Type), typeof(Application), new UIPropertyMetadata(ControllerChanged));
    private static void ControllerChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        if(e.NewValue != null)
        {
            ApplicationControllerBase.DefaultApplicationController = (ApplicationControllerBase)((Type)e.NewValue).GetConstructor(Type.EmptyTypes).Invoke(null);
        }
        ((FrameworkElement)d).DataContext = ApplicationControllerBase.DefaultApplicationController;
    }
}
 
The ApplicationControllerBase is my own base class for an application viewmodel, and the Default static property is useful for quickly navigating to the top tier from within a deep part.
 
To set the DataContext in a window, I then add this to the XAML:
<Window x:Class="..."
  xmlns:app="..."
  xmlns:vm="..."
  vm:Application.Controller="app:..."
  ... />
 
Using this, we could pull in the application level data context anywhere in xaml, by using the vm:Application.Controller="app:..." tag on any element, it would get its DataContext set to the application view model.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Morten Nilsen

Norway Norway
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Comments and Discussions

 
Generalwww.bags-shoes.com www bags-shoes com bags shoes,gucci book... Pinmemberbagsshoes2822-Nov-10 23:23 
GeneralWell, it doesn't all have to be new.. Just trying to help ne... PinmemberMorten Nilsen22-Nov-10 21:25 
GeneralReason for my vote of 2 Nothing new here. Just about every M... PinmemberSledgeHammer0122-Nov-10 9:48 

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