fractorium/Source/Fractorium/LibraryTreeWidget.cpp

#include "FractoriumPch.h"
#include "LibraryTreeWidget.h"
#include "Fractorium.h"

/// <summary>
/// Set a pointer to the main window.
/// </summary>
/// <param name="f">Pointer to the main Fractorium object</param>
void LibraryTreeWidget::SetMainWindow(Fractorium* f)
{
	m_Fractorium = f;
}

/// <summary>
/// Process the drop event to allow for moving items around inside of the tree.
/// </summary>
/// <param name="de">Pointer to the QDropEvent object</param>
void LibraryTreeWidget::dropEvent(QDropEvent* de)
{
	QModelIndex droppedIndex = indexAt(de->pos());
	auto items = selectionModel()->selectedRows();

	if (!droppedIndex.isValid())//Don't process drop because it's outside of the droppable area.
	{
		de->ignore();
		return;
	}
	else if (!items.empty())//Actually do the drop and move the item to a new location.
	{
		// get the list of the items that are about to be dragged
		int i, row = droppedIndex.row();
		DropIndicatorPosition dp = dropIndicatorPosition();
		QList<QTreeWidgetItem*> dragItems = selectedItems();

		if (dp == QAbstractItemView::BelowItem)
			row++;

		auto itemat = this->itemFromIndex(droppedIndex);
		QTreeWidget::dropEvent(de);//This internally changes the order of the items.

		//Qt has a long standing major bug that rearranges the order of disjoint selections when
		//The drop location is in between the disjoint regions.
		//This is an attempt to correct for that bug by removing the dropped items, then re-inserting them
		//in the order they were selected.
		//This bug remains present as of Qt 5.8: https://bugreports.qt.io/browse/QTBUG-45320
		if (auto top = topLevelItem(0))
		{
			if (itemat)
			{
				auto offsetitem = this->indexFromItem(itemat);

				if (dp == QAbstractItemView::BelowItem)
				{
					auto itemrow = offsetitem.row() + 1;

					for (i = 0; i < dragItems.size(); i++)
					{
						if (itemrow < top->childCount())
							top->takeChild(itemrow);
					}

					for (i = 0; i < dragItems.size(); i++)
					{
						auto offset = i + itemrow;

						if (offset <= top->childCount())
							top->insertChild(offset, dragItems[i]);
					}
				}
				else
				{
					auto itemrow = offsetitem.row();//Will be at least 1 if dropped above it.
					auto offset = itemrow;

					for (i = 0; i < dragItems.size(); i++)
					{
						offset--;

						if (offset < top->childCount())
							top->takeChild(offset);
					}

					for (i = 0; i < dragItems.size(); i++)
					{
						if (offset <= top->childCount())
							top->insertChild(offset, dragItems[i]);

						offset++;
					}
				}
			}
		}

		QTimer::singleShot(500, [ = ]() { m_Fractorium->m_Controller->MoveLibraryItems(items, row); });//Need to fire this after this event has internally reshuffled the items.
	}
}