Question

So I have a Border with a TranslateTransform so that I can move it around my window. Within the contents of the Border I have a number of controls plus a ScrollViewer. The dragging works fine but when I click the scrollbar the whole border jumps so that my cursor is now over the last point at which I clicked. Very annoying and I can’t see why it’s happening to my scrollbar but not my other controls.

(I’m using Denis Morozov’s simple, excellent guide http://denismorozov.blogspot.ie/2008/01/drag-controls-in-wpf-using.html)

Here’s what I’m doing in code;

private void Canvas_MouseDown(object sender, MouseButtonEventArgs e)
    {
        this.current.X = Mouse.GetPosition((IInputElement)sender).X;
        this.current.Y = Mouse.GetPosition((IInputElement)sender).Y;

        // Ensure object receives all mouse events.
        this.current.InputElement.CaptureMouse();
    }

    private void Canvas_MouseUp(object sender, MouseButtonEventArgs e)
    {
        if (this.current.InputElement != null)
            this.current.InputElement.ReleaseMouseCapture();
    }

    private void Canvas_MouseMove(object sender, MouseEventArgs e)
    {
        // if mouse is down when its moving, then it's dragging current
        if (e.LeftButton == MouseButtonState.Pressed)
            this.current.IsDragging = true;
        else
            this.current.IsDragging = false;

        if (this.current.IsDragging && current.InputElement != null)
        {
            // Retrieve the current position of the mouse.
            double newX = Mouse.GetPosition((IInputElement)sender).X;
            double newY = Mouse.GetPosition((IInputElement)sender).Y;

            // Reset the location of the object (add to sender's renderTransform

            // newPosition minus currentElement's position
            Transform rt = ((UIElement)this.current.InputElement).RenderTransform;
            double offsetX = rt.Value.OffsetX;
            double offsetY = rt.Value.OffsetY;
            rt.SetValue(TranslateTransform.XProperty, offsetX + newX - current.X);
            rt.SetValue(TranslateTransform.YProperty, offsetY + newY - current.Y);

            // Update position of the mouse
            current.X = newX;
            current.Y = newY;
        }
    }

    public void MouseLeftBtnDown(object sender, MouseButtonEventArgs e)
    {
        this.current.InputElement = (IInputElement)sender;
    }

Answer 1

Found it actually in the comments on Denis’ page. Problem lay in not resetting things on Canvas_MouseUp. That method should actually be;

if (this.current.InputElement != null)
{
this.current.IsDragging = false;
this.current.InputElement.ReleaseMouseCapture();
this.current.InputElement = null;
}

Now works like a charm 😉