Handling DataGrid.SelectedItems in an MVVM-friendly manner

.NET, Blend, MVVM, Silverlight, Technical stuff, Work, WPF
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This post was imported from my old blog and had 31 comments which are included as a screenshot at the end of this post.

An interesting question from one of the MVVM Light users today:

Is there an MVVM-friendly way to get a DataGrid’s SelectedItems into the ViewModel?

The issue there is as old as the DataGrid (that’s not very old but still): SelectedItem (singular) is a DependencyProperty and can be databound to a property in the ViewModel. SelectedItems (plural) is not a DependencyProperty.

Thankfully the answer is very simple: Use EventToCommand to call a Command in the ViewModel, and pass the SelectedItems collection as parameter. For example, if the command in the ViewModel is declared as follows:

public RelayCommand<IList> SelectionChangedCommand
    private set;

and (in the MainViewModel constructor):

SelectionChangedCommand = new RelayCommand<IList>(
    items =>
        if (items == null)
            NumberOfItemsSelected = 0;

        NumberOfItemsSelected = items.Count;

Then the XAML markup becomes:

<sdk:DataGrid x:Name="MyDataGrid"
                ItemsSource="{Binding Items}">
        <i:EventTrigger EventName="SelectionChanged">
                Command="{Binding SelectionChangedCommand}"
                CommandParameter="{Binding SelectedItems,
                    ElementName=MyDataGrid}" />

I slapped a quick sample and published it here (VS2010, SL4 but the concept works in SL3 and WPF too).



GalaSoft Laurent Bugnion
Laurent Bugnion (GalaSoft)

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This post was imported from my old blog. Original comments screenshot: 12-11-2013 9-05-25 PM

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