How to delete selected row from a datagridwith context menu in Silverlight?

I need to be able to delete a selected row from a datagrid with "Delete” context menu item. I have hard time finding the path to the selected row. I am wondering if someone can look at the code below and let me know what will be the appropriate to do within my code. Thank you in advance.

XAML:

<UserControl.DataContext>     
    <local:MainPage_ViewModel/> 
</UserControl.DataContext>  
<StackPanel Orientation="Horizontal">  

    <data:DataGrid ItemsSource="{Binding Coordinates}" AutoGenerateColumns="False" Margin="10">
        <!-- ContextMenu -->
          <toolkit:ContextMenuService.ContextMenu>
             <toolkit:ContextMenu x:Name="Menu" >
                <toolkit:MenuItem x:Name="Edit" />
                <toolkit:MenuItem x:Name="Delete" Tag="{Binding}" Click="Button_Click" />
            </toolkit:ContextMenu>
        </toolkit:ContextMenuService.ContextMenu>      
        <data:DataGrid.Columns>             
            <data:DataGridTextColumn Header="X Position" Width="100" Binding="{Binding X}"/>             
            <data:DataGridTextColumn Header="Y Position" Width="100" Binding="{Binding Y}"/>             
            <data:DataGridTemplateColumn Header="Delete Item" Width="100">                 
                <data:DataGridTemplateColumn.CellTemplate>                     
                    <DataTemplate>                         
                        <Button Content="Delete" Tag="{Binding}" Click="Button_Click"/>                     
                    </DataTemplate>                 
                </data:DataGridTemplateColumn.CellTemplate>             
            </data:DataGridTemplateColumn>         
        </data:DataGrid.Columns>     
    </data:DataGrid>

Code behind:

public partial class MainPage : UserControl
{
    public MainPage()
    {
        InitializeComponent();         
        this.viewModel = this.DataContext as MainPage_ViewModel; 
    }

    private MainPage_ViewModel viewModel;      
    private void Button_Click(object sender, RoutedEventArgs e)     
    {         
        viewModel.DeleteCoordinate((sender as Button).Tag as Coordinate_DataViewModel);     
    }
}

ViewModel:

public class MainPage_ViewModel : INotifyPropertyChanged 
{
    public MainPage_ViewModel()
    {
        coordinates.Add(new Coordinate_DataViewModel(new Coordinate_Model() { X = 1, Y = 2 }));         
        coordinates.Add(new Coordinate_DataViewModel(new Coordinate_Model() { X = 2, Y = 4 }));         
        coordinates.Add(new Coordinate_DataViewModel(new Coordinate_Model() { X = 3, Y = 6 }));         
        coordinates.Add(new Coordinate_DataViewModel(new Coordinate_Model() { X = 4, Y = 8 }));         
        coordinates.Add(new Coordinate_DataViewModel(new Coordinate_Model() { X = 5, Y = 10 }));         
        coordinates.Add(new Coordinate_DataViewModel(new Coordinate_Model() { X = 6, Y = 12 }));
    }

    public ObservableCollection<Coordinate_DataViewModel> Coordinates     
    {         
        get { return coordinates; }         
        set          
        {             
            if (coordinates != value)             
            {                 
                coordinates = value;                 
                OnPropertyChanged("Coordinates");             
            }         
        }     
    }     
    private ObservableCollection<Coordinate_DataViewModel> coordinates = new ObservableCollection<Coordinate_DataViewModel>();      
    public event PropertyChangedEventHandler PropertyChanged;      

    pu开发者_如何学Cblic void OnPropertyChanged(string propertyName)     
    {         
        if (PropertyChanged != null)         
        {             
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));         
        }     
    }      

    public void DeleteCoordinate(Coordinate_DataViewModel dvmToDelete)     
    {         
        coordinates.Remove(dvmToDelete);     
    }

    public void UpdateCoordinate(Coordinate_DataViewModel dvmToDelete)
    {

    }
}

//Model
public class Coordinate_Model 
{     
    public double X;     
    public double Y; 
} 

//DataViewModel
public class Coordinate_DataViewModel 
{     
    public Coordinate_DataViewModel(Coordinate_Model model)     
    {         
        this.underlyingModel = model;     
    }     

    private Coordinate_Model underlyingModel;      
    public double X     
    {         
        get { return underlyingModel.X; }         
        set { underlyingModel.X = value; }     
    }      

    public double Y     
    {         
        get { return underlyingModel.Y; }         
        set { underlyingModel.Y = value; }     
    }      public string XYCoordinate     

    {         
        get { return "(" + X + "," + Y + ")"; }     
    } 
}

Update your datagrid to bind to a selected item on your viewModel. Update your datagrid as follows:

<data:DataGrid ItemsSource="{Binding Coordinates}" AutoGenerateColumns="False" Margin="10" SelectedItem="{Binding SelectedItem, Mode=TwoWay}">

On your view model, add the following property:

public Coordinate_DataViewModel SelectedItem
    {
        get { return selectedItem; }
        set { selectedItem = value; }
    }
    private Coordinate_DataViewModel selectedItem;

Then, you could add the following method to your view model:

public void DeleteSelectedItem()
    {
        DeleteCoordinate(this.SelectedItem);
    }

Now, hook up your 'Delete' button on the context menu to the DeleteSelectedItem() and you should be good to go.

Hope this helps!

Edit for comment response: Here's an example of what you could add to implement the issue you mentioned in the comments where you don't always want to be able to delete the item. Notice i added the INotifyPropertyChanged to the setter of the SelectedItem so that the bindings of IsDeletable will be updated.

public Coordinate_DataViewModel SelectedItem
    {
        get { return selectedItem; }
        set 
        { 
            selectedItem = value;
            OnPropertyChanged("IsDeletable");
        }
    }
    private Coordinate_DataViewModel selectedItem;

    public Visibility IsDeletable
    {
        get
        {
            if (SelectedItem.Y == 2)
            {
                return Visibility.Collapsed;
            }

            return Visibility.Visible;
        }
    }

Bind the data grids SelectedItem to a property in your ViewModel. Use commanding to fire a method in your ViewModel when the delete button is clicked. Then remove the item from the ObservableCollection.

If you want to delete multiple items: Handling DataGrid.SelectedItems in an MVVM-friendly manner