Handling DataGrid.SelectedItems in an MVVM-friendly manner
- by Laurent Bugnion
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
{
get;
private set;
}and (in the MainViewModel constructor):SelectionChangedCommand = new RelayCommand<IList>(
items =>
{
if (items == null)
{
NumberOfItemsSelected = 0;
return;
}
NumberOfItemsSelected = items.Count;
});
Then the XAML markup becomes:<sdk:DataGrid x:Name="MyDataGrid"
ItemsSource="{Binding Items}">
<i:Interaction.Triggers>
<i:EventTrigger EventName="SelectionChanged">
<cmd:EventToCommand
Command="{Binding SelectionChangedCommand}"
CommandParameter="{Binding SelectedItems,
ElementName=MyDataGrid}" />
</i:EventTrigger>
</i:Interaction.Triggers>
</sdk:DataGrid>
I slapped a quick sample and published it here (VS2010, SL4 but the concept works in SL3 and WPF too).
Cheers!
Laurent
Laurent Bugnion (GalaSoft) Subscribe | Twitter | Facebook | Flickr | LinkedIn
