/// <summary>
/// Trigger a dragging event when the user moves the mouse while the left mouse button is pressed
/// </summary>
protected override void OnMouseMove(MouseEventArgs e)
{
if (_userClickedThisElement && !_dragActive)
{
_dragActive = true;
DragStart?.Invoke(this, e);
}
if (_dragActive)
{
Point curMouseScreenPos = e.GetPosition(this);
if (!curMouseScreenPos.Equals(_previousMouseScreenPos))
{
double xDelta = curMouseScreenPos.X - _previousMouseScreenPos.X;
double yDelta = curMouseScreenPos.Y - _previousMouseScreenPos.Y;
var dragEvent = new DragMoveEventArgs(e, xDelta, yDelta);
DragMove?.Invoke(this, dragEvent);
ApplyDragToChildren(dragEvent);
_previousMouseScreenPos = curMouseScreenPos;
}
}
base.OnMouseMove(e);
}
private void ApplyDragToChildren(DragMoveEventArgs drag)
{
foreach (UIElement cur in Children)
{
double prevLeft = Canvas.GetLeft(cur);
if (Double.IsNaN(prevLeft))
{
prevLeft = 0;
}
double prevTop = Canvas.GetTop(cur);
if (Double.IsNaN(prevTop))
{
prevTop = 0;
}
Canvas.SetLeft(cur, prevLeft + (drag.DeltaX));
Canvas.SetTop(cur, prevTop + (drag.DeltaY));
}
}
