WT-8638: drag/drop between rows in WAbstractItemView

Author: korneel-emweb

resources/themes/bootstrap/2/wt.css

@@ -644,6 +644,26 @@
   background-color: #EEEEEE;
   outline: 1px dotted black;
 }
+
+.Wt-drop-site-top {
+    box-shadow: 0 2px 0 #000 inset;
+    position: absolute;
+    top: 0px;
+    left: 0px;
+    width:100%;
+    height:100%;
+    pointer-events: none;
+}
+.Wt-drop-site-bottom {
+    box-shadow: 0 -2px 0 #000 inset;
+    position: absolute;
+    top: 0px;
+    left: 0px;
+    width:100%;
+    height:100%;
+    pointer-events: none;
+}
+
 body.Wt-rtl .Wt-itemview .Wt-tv-rh,
 body.Wt-rtl .Wt-itemview .Wt-tv-sh {
   float: left;

resources/themes/bootstrap/3/wt.css

@@ -712,6 +712,25 @@ fieldset[disabled] .Wt-slider-v .handle.active {
   outline: 1px dotted black;
 }
 
+.Wt-drop-site-top {
+    box-shadow: 0 2px 0 #000 inset;
+    position: absolute;
+    top: 0px;
+    left: 0px;
+    width:100%;
+    height:100%;
+    pointer-events: none;
+}
+.Wt-drop-site-bottom {
+    box-shadow: 0 -2px 0 #000 inset;
+    position: absolute;
+    top: 0px;
+    left: 0px;
+    width:100%;
+    height:100%;
+    pointer-events: none;
+}
+
 body.Wt-rtl .Wt-itemview .Wt-tv-rh,
 body.Wt-rtl .Wt-itemview .Wt-tv-sh {
   float: left;

resources/themes/default/wt.css

@@ -931,6 +931,26 @@ body.Wt-rtl .Wt-itemview .Wt-tv-sh {
     outline: 1px dotted black;
 }
 
+.Wt-drop-site-top {
+    box-shadow: 0 2px 0 #000 inset;
+    position: absolute;
+    top: 0px;
+    left: 0px;
+    width:100%;
+    height:100%;
+    pointer-events: none;
+}
+.Wt-drop-site-bottom {
+    box-shadow: 0 -2px 0 #000 inset;
+    position: absolute;
+    top: 0px;
+    left: 0px;
+    width:100%;
+    height:100%;
+    pointer-events: none;
+}
+
+
 /*
  * WTableView
  */

resources/themes/polished/wt.css

@@ -995,6 +995,25 @@ body.Wt-rtl .Wt-itemview .Wt-tv-sh {
     outline: 1px dotted black;
 }
 
+.Wt-drop-site-top {
+    box-shadow: 0 2px 0 #000 inset;
+    position: absolute;
+    top: 0px;
+    left: 0px;
+    width:100%;
+    height:100%;
+    pointer-events: none;
+}
+.Wt-drop-site-bottom {
+    box-shadow: 0 -2px 0 #000 inset;
+    position: absolute;
+    top: 0px;
+    left: 0px;
+    width:100%;
+    height:100%;
+    pointer-events: none;
+}
+
 /*
  * WTableView
  */

src/Wt/WAbstractItemModel.C

@@ -290,8 +290,6 @@ void WAbstractItemModel::dropEvent(const WDropEvent& e, DropAction action,
 	}
 
 	++r;
-      } else {
-	  
       }
     }
 
@@ -311,6 +309,66 @@ void WAbstractItemModel::dropEvent(const WDropEvent& e, DropAction action,
   }
 }
 
+void WAbstractItemModel::dropEvent(const WDropEvent& e, DropAction action,
+				   const WModelIndex& pindex, Wt::Side side)
+{
+  WItemSelectionModel *selectionModel
+    = dynamic_cast<WItemSelectionModel *>(e.source());
+  if (selectionModel) {
+    auto sourceModel = selectionModel->model();
+
+    const WModelIndex& parent = pindex.parent();
+    int row = !pindex.isValid() ? rowCount() :
+      side == Side::Bottom ? pindex.row()+1 : pindex.row();
+
+    /*
+     * (1) Insert new rows (or later: cells ?)
+     */
+    if (!insertRows(row, selectionModel->selectedIndexes().size(), parent)) {
+      LOG_ERROR("dropEvent(): could not insertRows()");
+      return;
+    }
+
+    /*
+     * (2) Copy data
+     */
+    WModelIndexSet selection = selectionModel->selectedIndexes();
+
+    int r = row;
+    for (WModelIndexSet::const_iterator i = selection.begin();
+	 i != selection.end(); ++i) {
+      WModelIndex sourceIndex = *i;
+      if (selectionModel->selectionBehavior() ==
+	  SelectionBehavior::Rows) {
+	WModelIndex sourceParent = sourceIndex.parent();
+
+	for (int col = 0; col < sourceModel->columnCount(sourceParent); ++col) {
+	  WModelIndex s = sourceModel->index(sourceIndex.row(), col,
+					     sourceParent);
+	  WModelIndex d = index(r, col, parent);
+	  copyData(sourceModel.get(), s, this, d);
+	}
+
+	++r;
+      }
+    }
+
+    /*
+     * (3) Remove original data
+     */
+    if (action == DropAction::Move) {
+      while (!selectionModel->selectedIndexes().empty()) {
+        WModelIndex i = Utils::last(selectionModel->selectedIndexes());
+
+        if (!sourceModel->removeRow(i.row(), i.parent())) {
+          LOG_ERROR("dropEvent(): could not removeRows()");
+          return;
+        }
+      }
+    }
+  }
+}
+
 void WAbstractItemModel::beginInsertColumns(const WModelIndex& parent, 
 					    int first, int last)
 {

src/Wt/WAbstractItemModel.h

@@ -555,6 +555,12 @@ class WT_API WAbstractItemModel : public WObject
    * abstract item models. Source item data is copied (but not the
    * source item's flags).
    *
+   * This method is overloaded for handling drop events on top of items
+   * or drop events between items (see Wt::DropLocation). This overload
+   * handles drops on top of items, but note that due to historical
+   * reasons it will also insert the items in between when called with
+   * DropAction::Move.
+   *
    * The location in the model is indicated by the \p row and
    * \p column within the \p parent index. If \p row is
    * -1, then the item is appended to the \p parent. Otherwise,
@@ -575,6 +581,29 @@ class WT_API WAbstractItemModel : public WObject
   virtual void dropEvent(const WDropEvent& e, DropAction action,
 			 int row, int column, const WModelIndex& parent);
 
+  /*! \brief Handles a drop event.
+   *
+   * The default implementation only handles generic drag&drop between
+   * abstract item models. Source item data is copied (but not the
+   * source item's flags).
+   *
+   * This method is overloaded for handling drop events on top of items
+   * or drop events between items. This overload handles drops between
+   * items. The drop was received relative to the \p index item and the \p side
+   * parameter will only be Wt::Top or Wt::Bottom.
+   *
+   * You may want to reimplement this method if you want to handle
+   * other mime-type data, or if you want to refine how the drop event
+   * of an item selection must be interpreted.
+   *
+   * \note Currently, only row selections are handled by the default
+   *       implementation.
+   *
+   * \sa mimeType(), WItemSelectionModel
+   */
+  virtual void dropEvent(const WDropEvent& e, DropAction action,
+                         const WModelIndex& index, Wt::Side side);
+
   /*! \brief Inserts one column.
    *
    * This is a convenience method that adds a single column, and is

src/Wt/WAbstractItemView.C

@@ -226,7 +226,6 @@ WAbstractItemView::WAbstractItemView()
     renderState_(RenderState::NeedRerender),
     currentSortColumn_(-1),
     dragEnabled_(false),
-    dropsEnabled_(false),
     selectionModel_(new WItemSelectionModel()),
     rowHeight_(20),
     headerLineHeight_(20),
@@ -575,10 +574,10 @@ void WAbstractItemView::dropEvent(const WDropEvent& e, const WModelIndex& index)
    * Here, we only handle standard drag&drop actions between abstract
    * item models.
    */
-  if (dropsEnabled_) {
+  if (enabledDropLocations_.test(DropLocation::OnItem)) {
     std::vector<std::string> acceptMimeTypes = model_->acceptDropMimeTypes();
 
-    for (unsigned i = 0; i < acceptMimeTypes.size(); ++i)
+    for (std::size_t i = 0; i < acceptMimeTypes.size(); ++i) {
       if (acceptMimeTypes[i] == e.mimeType()) {
 	// we define internal by sharing the same selection model...
 	// currently selection models cannot be shared
@@ -587,15 +586,31 @@ void WAbstractItemView::dropEvent(const WDropEvent& e, const WModelIndex& index)
 	DropAction action = internal ? 
 	  DropAction::Move : DropAction::Copy;
 
-	// TODO: (later) we need to interpret the event location
-	// (e.mouseEvent().widget().y) For now we will implement to
-	// add as a sibling before the index
 	model_->dropEvent(e, action,
 			  index.row(), index.column(), index.parent());
 
 	setSelectedIndexes(WModelIndexSet());
 	return;
       }
+    }
+  }
+
+  WCompositeWidget::dropEvent(e);
+}
+
+void WAbstractItemView::dropEvent(const WDropEvent& e, const WModelIndex& index, Side side)
+{
+  if (enabledDropLocations_.test(DropLocation::BetweenRows)) {
+    std::vector<std::string> acceptMimeTypes = model_->acceptDropMimeTypes();
+
+    for (std::size_t i = 0; i < acceptMimeTypes.size(); ++i) {
+      if (acceptMimeTypes[i] == e.mimeType()) {
+        model_->dropEvent(e, DropAction::Move, index, side);
+
+        setSelectedIndexes(WModelIndexSet());
+        return;
+      }
+    }
   }
 
   WCompositeWidget::dropEvent(e);
@@ -617,7 +632,7 @@ void WAbstractItemView::configureModelDragDrop()
   std::vector<std::string> acceptMimeTypes = model_->acceptDropMimeTypes();
 
   for (unsigned i = 0; i < acceptMimeTypes.size(); ++i)
-    if (dropsEnabled_)
+    if (!enabledDropLocations_.empty())
       acceptDrops(acceptMimeTypes[i], "Wt-drop-site");
     else
       stopAcceptDrops(acceptMimeTypes[i]);
@@ -626,11 +641,20 @@ void WAbstractItemView::configureModelDragDrop()
 
 void WAbstractItemView::setDropsEnabled(bool enable)
 {
-  if (dropsEnabled_ != enable) {
-    dropsEnabled_ = enable;
+  if (enable)
+    setEnabledDropLocations(DropLocation::OnItem);
+  else
+    setEnabledDropLocations(None);
+}
 
-    configureModelDragDrop();
-  }
+void WAbstractItemView::setEnabledDropLocations(WFlags<DropLocation> dropLocations) {
+  if (enabledDropLocations_ == dropLocations)
+    return;
+
+  enabledDropLocations_ = dropLocations;
+  configureModelDragDrop();
+
+  scheduleRender();
 }
 
 void WAbstractItemView::checkDragSelection()