Wpf – MVVM: CollectionView in ViewModel or CollectionViewSource in xaml

collectionsmvvmwpf

I'm developing a WPF application using the MVVM pattern and I need to display a list of items in a ListView (with filtering), with the fields of the selected item displayed in a Master/Detail view. I'm torn between the following two ways of doing this:

Exposing a CollectionView in my ViewModel, and binding to this.
Exposing a plain IList in my ViewModel, and using CollectionViewSource to create the CollectionView in XAML.

Is there an accepted way of doing this? Any thoughts on the best way?

Best Answer

I do the former (expose CollectionView from the VM) but what really matters is where your filtering logic is. That should definitely be in the VM so that it can be tested, even if the view has to wire up the CollectionViewSource to the VM. That said, I don't think there's anything particularly nasty or anti-MVVM about exposing a CollectionView from your VM.

Related Solutions

C# – How should the ViewModel close the form

I was inspired by Thejuan's answer to write a simpler attached property. No styles, no triggers; instead, you can just do this:

<Window ...
        xmlns:xc="clr-namespace:ExCastle.Wpf"
        xc:DialogCloser.DialogResult="{Binding DialogResult}">

This is almost as clean as if the WPF team had gotten it right and made DialogResult a dependency property in the first place. Just put a bool? DialogResult property on your ViewModel and implement INotifyPropertyChanged, and voilà, your ViewModel can close the Window (and set its DialogResult) just by setting a property. MVVM as it should be.

Here's the code for DialogCloser:

using System.Windows;

namespace ExCastle.Wpf
{
    public static class DialogCloser
    {
        public static readonly DependencyProperty DialogResultProperty =
            DependencyProperty.RegisterAttached(
                "DialogResult",
                typeof(bool?),
                typeof(DialogCloser),
                new PropertyMetadata(DialogResultChanged));

        private static void DialogResultChanged(
            DependencyObject d,
            DependencyPropertyChangedEventArgs e)
        {
            var window = d as Window;
            if (window != null)
                window.DialogResult = e.NewValue as bool?;
        }
        public static void SetDialogResult(Window target, bool? value)
        {
            target.SetValue(DialogResultProperty, value);
        }
    }
}

I've also posted this on my blog.

R – How to pass a specific viewmodel object in a button’s CommandParam

Something similiar to what Paul has shown is where your view model will know which item is currently selected. I.e.

public class MyVM
{
 public ObservableCollection<MyObject> MyCollection { get; set; }
 public MyObject CurrentItem { get; set; }
}

Your XAML can then be simply

CommandParameter="{Binding Path=CurrentItem}"

As long as your master pane sets the CurrentItem property when you select it, your command can simple have the CurrentItem set as the command parameter.

Best Answer

Related Solutions

C# – How should the ViewModel close the form

R – How to pass a specific viewmodel object in a button’s CommandParam

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