MVVM Experts - How would you...

[Karl Shifflett]

Got the following two part question today on my blog.

 

I know how I would solve this, but was wondering what the experts would do...

 

I tried the MVVM design pattern, and found a few roadblocks, mostly about events. For example, how do I bind a double click on a listbox item to an event? How do I bind a click on a gridview header (to sort rows) into an event?

 

Cheers,

 

Karl

[Corrado Cavalli]

That’s the first question I get when I speak about MVVM, my personal approach is to use an attached behavior that links the event to related command.

 

-Corrado

[Mike Brown]

I agree, sorting a gridview is a perfect example of how attached behaviors are useful ;)

[Sacha Barber]

I think attached behavior is the way to go to

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Subject: [WPF Disciples] MVVM Experts - How would you...

Date: Thu, 29 Jan 2009 06:49:23 -0800
From: ka...@littlerichie.com
To: wpf-di...@googlegroups.com

---

Beyond Hotmail - see what else you can do with Windows Live Find out more!

[Bill Kempf]

Yep. Today, it's probably the best answer.

--
Quidquid latine dictum sit, altum sonatur.
- Whatever is said in Latin sounds profound.

War is peace. Freedom is slavery. Bugs are features.

[Laurent Bugnion, GalaSoft [MVP, MCP]]

Hey Corrado,

 

Do you have a sample to show me?

 

Cheers,

Laurent

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[Corrado Cavalli]

Here it is:

 

  public class SelectionBehavior

  {

    public static DependencyProperty SelectionChangedProperty =

            DependencyProperty.RegisterAttached("SelectionChanged",

            typeof(ICommand),

            typeof(SelectionBehavior),

            new UIPropertyMetadata(SelectionBehavior.SelectedItemChanged));

 

 

    public static void SetSelectionChanged(DependencyObject target, ICommand value)

    {

      target.SetValue(SelectionBehavior.SelectionChangedProperty, value);

    }

 

    private static void SelectedItemChanged(DependencyObject target, DependencyPropertyChangedEventArgs e)

    {

      Selector element = target as Selector;

      if (element == null) throw new InvalidOperationException("This behavior can be attached to Selector item only.");

      if ((e.NewValue != null) && (e.OldValue == null))

      {

        element.SelectionChanged += SelectionChanged;

      }

      else if ((e.NewValue == null) && (e.OldValue != null))

      {

        element.SelectionChanged -= SelectionChanged;

      }

    }

 

    private static void SelectionChanged(object sender, System.Windows.Controls.SelectionChangedEventArgs e)

    {

      UIElement element = (UIElement)sender;

      ICommand command = (ICommand)element.GetValue(SelectionBehavior.SelectionChangedProperty);

      command.Execute(null);

    }

  }

 

Use:

 

<ComboBox local:SelectionBehavior.SelectionChanged="{Binding SelectManufacturerCommand}" 

              ItemsSource="{Binding Manufacturers}"

              Height="23" Margin="12,38,15,0" Name="comboBox1" VerticalAlignment="Top" />

 

This invokes SelectManufacturerCommand when listbox selection changed

 

-Corrado

 

From: wpf-di...@googlegroups.com [mailto:wpf-di...@googlegroups.com] On Behalf Of Laurent Bugnion, GalaSoft [MVP, MCP]

Sent: giovedì 29 gennaio 2009 17:09
To: wpf-di...@googlegroups.com

Subject: [WPF Disciples] Re: MVVM Experts - How would you...

 

Hey Corrado,

 

Do you have a sample to show me?

 

Cheers,

Laurent

 

From: wpf-di...@googlegroups.com [mailto:wpf-di...@googlegroups.com] On Behalf Of Corrado Cavalli

Sent: Thursday, January 29, 2009 4:00 PM

No virus found in this incoming message.

[Karl Shifflett]

You guys are the Bomb.  Nice example Corrado!

[Corrado Cavalli]

Thank you Sir! ;-)

 

From: wpf-di...@googlegroups.com [mailto:wpf-di...@googlegroups.com] On Behalf Of Karl Shifflett
Sent: giovedì 29 gennaio 2009 17:50
To: wpf-di...@googlegroups.com
Subject: [WPF Disciples] Re: MVVM Experts - How would you...

 

You guys are the Bomb.  Nice example Corrado!

[Peter O'Hanlon]

I just got to this thread and thought I could answer it, and lo and behold Corrado's done a bang up job. Nice one Corrado.

--
Peter O'Hanlon

[Marlon Grech]

ok... some marketing here...... :P

http://marlongrech.wordpress.com/2008/12/13/attachedcommandbehavior-v2-aka-acb/

AttachedCommandBehaviors :) this is what I use....

Regards
Marlon
WPF Blog - http://marlongrech.wordpress.com/

[Laurent Bugnion, GalaSoft [MVP, MCP]]

Perfect, thanks Corrado.

 

Commands were a domain where I must admit I was always a little weak, but since I started using Josh Smith’s RelayCommand, I am totally digging it. With your behavior, it is now possible to use commands for more than “just” ICommandSource controls, this is really cool.

 

Fantastic J