WPF Getting mouse coordinates within viewmodel

Question

I have a WPF project (C#, MVVM Light, Visual Studio 2010).

I have a bit of a problem regarding separation of concerns (MVVM) which basically is this: I have a command in a view model. I have a context menu that I want to call that command. So far so good. The problem is that the command needs to coordinates that the mouse was clicked.

To be a little more specific, the ContextMenu only appears if you click on a particular Canvas control, and it's the coordinates within said Canvas control that I want.

The easy way to do this is to manage it all in the code behind of the XAML document (and I have been able to do it that way), but I'd rather have it within my ViewModel if I can do so. The reason is that there are calls to my data model within this command so we end up with a problem of separation.

I am aware of PassEventArgsToCommand, and I'm aware that it's a bad practise, however in this case I'm not sure I can see a way around it. So for the moment I did try that, and it looks like this:

<ContextMenu x:Key="BackgroundMenu">
            <MenuItem Header="Add new node here">
                <i:Interaction.Triggers>
                    <i:EventTrigger EventName="Click">
                        <cmd:EventToCommand Command="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type ContextMenu}}, Path=PlacementTarget.DataContext.AddNewNodeAtLocationCommand}" PassEventArgsToCommand="True"/>
                    </i:EventTrigger>
                </i:Interaction.Triggers>
            </MenuItem> 
        </ContextMenu>

So now my command, within the view model, looks like this:

void AddNewNodeAtLocationExecute(RoutedEventArgs e)
    {

        return;
    }

Within that method I'd like to get those mouse coordinates, but I don't know if it's possible. e.OriginalSource is 'MenuItem', which doesn't help much.

So how can I do this? Can I do this? Or should I just have this one command handled by the code behind? Said code will involve a call to the database, which is why I'm being so particular about the separation.

Thanks in advance.

Do you want the actual mouse coordinates or the x and y coordinates of the element within the Canvas? — mm8, Oct 13 '17 at 10:29

score 0 · Answer 1 · answered Oct 12 '17 at 20:40

Well I stumbled across this question which speaks about separation of concerns and what not.

In the end I did a merging of the two ideas I had. Firstly, the ContextMenu simply links to the code behind. At that point I get the coordinates I want. Then that code behind gets the DataContext of the view (where the command I want is) and calls the Execute method (having first checked the 'can' method).

I suppose it's as ideal as you're going to get.

WPF Getting mouse coordinates within viewmodel

1 Answers1