WPF DataGrid: CommandBinding to a double click instead of using Events

Question

I know how to use the MouseDoubleClick event with my DataGrid to grab the selectedvalue, but how would one go about using command bindings instead? That way my ViewModel can handle the logic.

So far I have the following:

<DataGrid Name="TestGrid" Grid.Row="2" Grid.ColumnSpan="2" AutoGenerateColumns="True" MouseDoubleClick="TestGrid_MouseDoubleClick"
          ItemsSource="{Binding Registrations}" SelectedValue="{Binding CurrentRegistration}" IsReadOnly="True" AlternationCount="2" GridLinesVisibility="None">

I want to get rid of MouseDoubleClick and replace it appropriately.

Jaclyn

Have you checked this post, provides entire solution... – Cookout

Answer 1

No need for attached behaviors or custom DataGrid subclasses here.

In your DataGrid, bind ItemsSource to an ICollectionView. The trick here is to set IsSynchronizedWithCurrentItem="True" which means the selected row will be the current item.

The second part of the trick is to bind CommandParameter to the current item with the forward slash syntax.

When a row is double clicked, the command will be executed with the clicked row as argument.

<DataGrid
    ItemsSource="{Binding CollectionView}"
    IsSynchronizedWithCurrentItem="True">
    <DataGrid.InputBindings>
        <MouseBinding
            MouseAction="LeftDoubleClick"
            Command="{Binding DoubleClickCommand}"
            CommandParameter="{Binding CollectionView/}"/>
    </DataGrid.InputBindings>
</DataGrid>

This is how a (simplified) version of the view model would look:

class MyViewModel
{
    public ICollectionView CollectionView { get; set; }

    public ICommand DoubleClickCommand { get; set; }
}

Nonsmoker

is the / in your {Binding CollectionView/} on purpose? – Stonechat

Yes, that makes it bind to the current item. Which when used with IsSynchronizedWithCurrentItem means the selected item. Here's a blog post. – Nonsmoker

Very neat solution. Also didn't know about the forward slash binding. Sometimes I'm really astonished where people know this kind of things from. Thank you! – Tycho

This is a good solution. But there is a drawback here. If one double clicks DataGrids' header, the command will be executed anyway. In some scenarios this might be undesirable thing for the developer. How can it be resolved that? – Weinreb

As I understand it, you can use the "CanExecute" part of the ICommand implementation to determine whether the parameter passed is a valid one for running the command on – Pleach

When I use the forward slash on the parameter, it always passes the item in the first row. I do have IsSynchronizedWithCurrentItem="True". The grid is bound to an ObservableCollection. Is there anything I'm missing re. the virtualisation? – Meadors

I give +1 but I think is hack anyway. – Piles

Note, that if IsReadOnly="False" for your DataGrid, then the first click may be stolen the selection mechanism. Set IsReadOnly="True" to fix that up. – Runty

Personally I don't like the Binding CollectionView/. Got this to work if you give the DataGrid a name and in the command parameter of the mouse binding do the following: CommandParameter="{Binding ElementName=SomeGridName, Path=SelectedItem}" – Stator

Why so many black magic in WPF/XAML? Where's the doc to describe what is the slash? – Szabo

Answer 2

Another solution is to add input bindings, and to bind the selectedItem to a property so you'll know which one was selected:

<DataGrid SelectedItem="{Binding SelectedItem}">
      <DataGrid.InputBindings>
          <MouseBinding Gesture="LeftDoubleClick" Command="{Binding SomeCommand}"/>
     </DataGrid.InputBindings>
</DataGrid>

Anticlinal

Nice and elegant. – Microcosm

Nice but there is an issue. Lets say you have a datagrid with multiple columns and the last column is not set to width=* and you double click to the far right in extra space after last column the selected item will not update and it will pass whatever the selected item was before. And if no selected item exists yet it will pass null. – Rupertruperta

Answer 3

Use this library

Sample binding to datagrid event:

<DataGrid xmlns:command="clr-namespace:AttachedCommandBehavior;assembly=AttachedCommandBehavior"
    command:CommandBehavior.Event="MouseDoubleClick"
    command:CommandBehavior.Command="{Binding TestCommand}" />

But this code is better, because raises on row clicks only:

<DataGrid>
    <DataGrid.Resources>
        <Style TargetType="DataGridRow">
            <Setter Property="command:CommandBehavior.Event" Value="MouseDoubleClick"/>
            <Setter Property="command:CommandBehavior.Command" Value="{Binding DataContext.TestCommand, RelativeSource={RelativeSource FindAncestor, AncestorType=DataGrid}}"/>
        </Style>
    </DataGrid.Resources>
</DataGrid>

Jahn

I like the library, but it seems to contain more than what I need (for the moment). I'll look at the library and if I need more than the double click command then perhaps this will contain other commands I wouldn't mind having. – Jaclyn

@Jaclyn You can also take a look at MVVM Light, it has the similar class and other classes which help to use the MVVM pattern. For me it is easier to add reference to a library than to copy the code, but it is controversial question whether to use 3rd party libraries or to write your own. – Jahn

Answer 4

Or, you could create a derived class

public class CustomDataGrid : DataGrid
{
    public ICommand DoubleClickCommand
    {
        get { return (ICommand)GetValue(DoubleClickCommandProperty); }
        set { SetValue(DoubleClickCommandProperty, value); }
    }

    // Using a DependencyProperty as the backing store for DoubleClickCommand.  This    enables animation, styling, binding, etc...
    public static readonly DependencyProperty DoubleClickCommandProperty =
        DependencyProperty.Register("DoubleClickCommand", typeof(ICommand), typeof(CustomDataGrid), new UIPropertyMetadata());

    public CustomDataGrid()
        : base()
    {            
        this.PreviewMouseDoubleClick += new MouseButtonEventHandler(CustomDataGrid_PreviewMouseDoubleClick);
    }


    void CustomDataGrid_PreviewMouseDoubleClick(object sender, MouseButtonEventArgs e)
    {
        if (DoubleClickCommand != null)
        {
            DoubleClickCommand.Execute(null);
        }
    }


}

and in XAML simply bind to the newly created command

<CustomDataGrid DoubleClickCommand="{Binding DoubleClickCommand}">

Pharos