public override bool Merge(CommandItem newitem)
        {
            SelectionMovedOrResizedCI newitemx = newitem as SelectionMovedOrResizedCI;

            // Ensure items are of the same type.
            if (newitemx == null ||
                newitemx._editingOperationCount != _editingOperationCount ||
                !StrokeCollectionsAreEqual(newitemx._selection, _selection))
            {
                return(false);
            }

            // Keep former oldrect, latter newrect.
            _newrect = newitemx._newrect;

            return(true);
        }
        public override bool Merge(CommandItem newitem)
        {
            StrokesAddedOrRemovedCI newitemx = newitem as StrokesAddedOrRemovedCI;

            if (newitemx == null ||
                newitemx._editingMode != _editingMode ||
                newitemx._editingOperationCount != _editingOperationCount)
            {
                return(false);
            }

            // We only implement merging for repeated point-erase operations.
            if (_editingMode != InkCanvasEditingMode.EraseByPoint)
            {
                return(false);
            }
            if (newitemx._editingMode != InkCanvasEditingMode.EraseByPoint)
            {
                return(false);
            }

            // Note: possible for point-erase to have hit intersection of >1 strokes!
            // For each newly hit stroke, merge results into this command item.
            foreach (Stroke doomed in newitemx._removed)
            {
                if (_added.Contains(doomed))
                {
                    _added.Remove(doomed);
                }
                else
                {
                    _removed.Add(doomed);
                }
            }
            _added.Add(newitemx._added);

            return(true);
        }
        /// <summary>
        /// Take the top item off the command stack.
        /// </summary>
        public void Redo()
        {
            if (!CanRedo)
            {
                throw new InvalidOperationException();
            }

            CommandItem item = _redoStack.Pop();

            // Invoke the redo operation, with change-tracking temporarily suspended.
            _disableChangeTracking = true;
            try
            {
                item.Redo();
            }
            finally
            {
                _disableChangeTracking = false;
            }

            //place this item on the undo stack
            _undoStack.Push(item);
        }
 // Allows multiple subsequent commands of the same type to roll-up into one
 // logical undoable/redoable command -- return false if newitem is incompatable.
 public abstract bool Merge(CommandItem newitem);