Question

I have a datagrid that potentially can have many rows. As the user right clicks one of the rows, I need to show a context menu for each of the rows and perform an action (same action but different data item according to the current selected row) when the user clicks the option.

What is the best strategy for this?

I’m fearing that a ContextMenu for each row is overkill even though I’m creating the menu using the ContextMenuOpening event, sort of a “lazy load” for the context menu. Should I only use one ContextMenu for the datagrid? But with this I would have some more work regarding the click event, to determine the correct row, etc.

Answer 1

As far as I know, some of the actions will be disabled or enabled depending on the row, so there is no point in a single ContextMenu for a DataGrid.

I have an example of the row-level context menu.

<UserControl.Resources>
    <ContextMenu  x:Key="RowMenu" DataContext="{Binding PlacementTarget.DataContext, RelativeSource={RelativeSource Self}}">
        <MenuItem Header="Edit" Command="{Binding EditCommand}"/>
    </ContextMenu>
    <Style x:Key="DefaultRowStyle" TargetType="{x:Type DataGridRow}">
        <Setter Property="ContextMenu" Value="{StaticResource RowMenu}" />
    </Style>
</UserControl.Resources>

<DataGrid RowStyle="{StaticResource DefaultRowStyle}"/>

The DataGrid must have a binding to a list of view models with commands:

public class ItemModel
{
    public ItemModel()
    {
        this.EditCommand = new SimpleCommand 
        { 
            ExecuteDelegate = _ => MessageBox.Show("Execute"), 
            CanExecuteDelegate = _ => this.Id == 1 
        };
    }
    public int Id { get; set; }
    public string Title { get; set; }
    public ICommand EditCommand { get; set; }
}

The context menu is created in the resources collection of the UserControl and I think there is only one object which is connected with datagrid rows by reference, not by value.

Here is another example of ContextMenu for a Command inside a MainViewModel. I suppose that DataGrid has a correct view model as the DataContext, also the CommandParameter attribute must be placed before the Command attribute:

    <ContextMenu  x:Key="RowMenu" DataContext="{Binding PlacementTarget.DataContext, RelativeSource={RelativeSource Self}}">
        <MenuItem Header="Edit" CommandParameter="{Binding}"
                  Command="{Binding DataContext.DataGridActionCommand, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=DataGrid}}" />
    </ContextMenu>

Models:

public class MainViewModel
{
    public MainViewModel()
    {
        this.DataGridActionCommand = new DelegateCommand<ItemModel>(m => MessageBox.Show(m.Title), m => m != null && m.Id != 2);
    }

    public DelegateCommand<ItemModel> DataGridActionCommand { get; set; }
    public List<ItemModel> Items { get; set; }
}

public class ItemModel
{
    public int Id { get; set; }
    public string Title { get; set; }
}

But there is a problem that MenuItem isn’t displayed as a disabled item if CanExecute returns false. The possible workaround is using a ParentModel property inside the ItemModel, but it doesn’t differ much from the first solution.
Here is example of above-described solution:

public class ItemModel
{
    public int Id { get; set; }
    public string Title { get; set; }
    public MainViewModel ParentViewModel { get; set; }
}

//Somewhere in the code-behind, create the main view model 
//and force child items to use this model as a parent model
var mainModel = new MainViewModel { Items = items.Select(item => new ItemViewModel(item, mainModel)).ToList()};

And MenuItem in XAML will be simplier:

<MenuItem Header="Edit" CommandParameter="{Binding}"
              Command="{Binding ParentViewModel.DataGridActionCommand}" />