Custom window drag handler interferes with scrollviewer bar drag

Question

I have a window with window style set to None that handles OnPreviewMouseDown, OnPreviewMouseUp, and OnMouseMove so that the window can be dragged from anywhere.

The windows code behind looks like this:

    bool inDrag;        

    protected override void OnPreviewMouseLeftButtonDown(MouseButtonEventArgs e)
    {
        base.OnPreviewMouseLeftButtonDown(e);            
        inDrag = true;
    }

    protected override void OnMouseMove(MouseEventArgs e)
    {
        base.OnMouseMove(e);
        if (inDrag && e.LeftButton == MouseButtonState.Pressed)
        {
            this.DragMove();
        }
    }

    protected override void OnPreviewMouseLeftButtonUp(MouseButtonEventArgs e)
    {
        base.OnPreviewMouseLeftButtonUp(e);
        if (inDrag)
        {
            inDrag = false;
        }
    }

Now problem is I have a large menu in this window that has a scroll bar which works with the scroll wheel and by clicking to a position on the scrollviewer but not when clicking and dragging the scroll bar itself. Also if I click and hold and move my cursor not on top of the window the scrolling works again. This has led me to believe that the above dragging implementation is blocking the scrollviewers drag functionality.

I tried manually raising the event with .RaiseEvent(e) in OnMouseMove but this causes a stack overflow exception when I move my mouse over the window.

How can I get my Scrollviewer to respond to mouse movements without removing my click and drag window behavior?

Answer 1

<!--ScrollViewer subscribed to PreviewMouseDown to set inDrag to false-->
    <ScrollViewer Visibility="Visible" Mouse.PreviewMouseDown="ScrollViewer_PreviewMouseDown">
        <!--The Grid fill all the available space and is subscribed to PreviewMouseDown event to set inDrag to true-->
        <Grid HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Mouse.PreviewMouseDown="Grid_PreviewMouseDown" Background="Transparent">
            <!--My menu-->
        </Grid>
    </ScrollViewer>

Note that if there is "blank space" (no Background set including that of the Content), the PreviewMouseDown event won't be raised despite the subscription. If needed, to work around that you can set the Background of the Grid to Transparent and the event will be raised even on seemingly blank space.