Dive list view: replace signal-magic by flag

In DiveListView, we have a very fundamental problem: When
On the one hand, we get informed of user-selection in the
DiveListView::selectionChanged() slot. This has to set the
correct flags in the C-backend.

On the other hand, sometimes we have to set the selection
programatically, e.g. when selecting a trip. This is done
by calling QItemSelectionModel::select().

But: this will *also* call into the above slot, in which
we can't tell whether it was a user interaction or an
internal call. This can lead to either infinite loops or
very inefficient behavior, because the current dive
is set numerous times.

The current code is aware of that and disconnects the
corresponding signal. This is scary, as these signals are
set internally by the model and view. Replace this
by a global "command executing" flag in DiveListNotifier.
The flag is set using a "marker" class, which resets the flag
once it goes out of scope (cf. RAII pattern).

In DiveListView, only process a selection if the flag is not
set. Otherwise simply call the QTreeView base class, to reflect
the new selection in the UI.

To have a common point for notifications of selection changes,
add such a signal to DiveListNotifier. This signal will be
used by the DiveListView as well as the Command-objects.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

1 files changed, 23 insertions, 15 deletions

diff --git a/desktop-widgets/divelistview.cpp b/desktop-widgets/divelistview.cpp
index ebeb1f6ef..2a0d7028c 100644
--- a/desktop-widgets/divelistview.cpp
+++ b/desktop-widgets/divelistview.cpp
@@ -24,6 +24,7 @@
 #include "desktop-widgets/divelistview.h"
 #include "qt-models/divepicturemodel.h"
 #include "core/metrics.h"
+#include "core/subsurface-qt/DiveListNotifier.h"
 
 DiveListView::DiveListView(QWidget *parent) : QTreeView(parent), mouseClickSelection(false), sortColumn(0),
 	currentOrder(Qt::DescendingOrder), dontEmitDiveChangedSignal(false), selectionSaved(false),
@@ -267,19 +268,17 @@ void DiveListView::selectTrip(dive_trip_t *trip)
 // works as expected
 void DiveListView::clearTripSelection()
 {
-	// we want to make sure no trips are selected
-	disconnect(selectionModel(), SIGNAL(selectionChanged(QItemSelection, QItemSelection)), this, SLOT(selectionChanged(QItemSelection, QItemSelection)));
-	disconnect(selectionModel(), SIGNAL(currentChanged(QModelIndex, QModelIndex)), this, SLOT(currentChanged(QModelIndex, QModelIndex)));
+	// This marks the selection change as being internal - ie. we don't process it further.
+	// TODO: This should probably be sold differently.
+	auto marker = diveListNotifier.enterCommand();
 
+	// we want to make sure no trips are selected
 	Q_FOREACH (const QModelIndex &index, selectionModel()->selectedRows()) {
 		dive_trip_t *trip = static_cast<dive_trip_t *>(index.data(DiveTripModel::TRIP_ROLE).value<void *>());
 		if (!trip)
 			continue;
 		selectionModel()->select(index, QItemSelectionModel::Deselect);
 	}
-
-	connect(selectionModel(), SIGNAL(selectionChanged(QItemSelection, QItemSelection)), this, SLOT(selectionChanged(QItemSelection, QItemSelection)));
-	connect(selectionModel(), SIGNAL(currentChanged(QModelIndex, QModelIndex)), this, SLOT(currentChanged(QModelIndex, QModelIndex)));
 }
 
 void DiveListView::unselectDives()
@@ -374,7 +373,7 @@ void DiveListView::selectDives(const QList<int> &newDiveSelection)
 		scrollTo(idx);
 	}
 	// now that everything is up to date, update the widgets
-	emit currentDiveChanged();
+	emit diveListNotifier.selectionChanged();
 	dontEmitDiveChangedSignal = false;
 	return;
 }
@@ -545,11 +544,20 @@ void DiveListView::currentChanged(const QModelIndex &current, const QModelIndex&
 
 void DiveListView::selectionChanged(const QItemSelection &selected, const QItemSelection &deselected)
 {
-	QItemSelection newSelected = selected.size() ? selected : selectionModel()->selection();
-	QItemSelection newDeselected = deselected;
+	if (diveListNotifier.inCommand()) {
+		// This is a programmatical change of the selection.
+		// Call the QTreeView base function to reflect the selection in the display,
+		// but don't process it any further.
+		QTreeView::selectionChanged(selected, deselected);
+		return;
+	}
 
-	disconnect(selectionModel(), SIGNAL(selectionChanged(QItemSelection, QItemSelection)), this, SLOT(selectionChanged(QItemSelection, QItemSelection)));
-	disconnect(selectionModel(), SIGNAL(currentChanged(QModelIndex, QModelIndex)), this, SLOT(currentChanged(QModelIndex, QModelIndex)));
+	// This is a manual selection change. This means that the core does not yet know
+	// of the new selection. Update the core-structures accordingly and select/deselect
+	// all dives of a trip if a trip is selected/deselected.
+	const QItemSelection &newDeselected = deselected;
+
+	QItemSelection newSelected = selected.size() ? selected : selectionModel()->selection();
 
 	Q_FOREACH (const QModelIndex &index, newDeselected.indexes()) {
 		if (index.column() != 0)
@@ -581,11 +589,11 @@ void DiveListView::selectionChanged(const QItemSelection &selected, const QItemS
 			select_dive(get_divenr(dive));
 		}
 	}
-	QTreeView::selectionChanged(selectionModel()->selection(), newDeselected);
-	connect(selectionModel(), SIGNAL(selectionChanged(QItemSelection, QItemSelection)), this, SLOT(selectionChanged(QItemSelection, QItemSelection)));
-	connect(selectionModel(), SIGNAL(currentChanged(QModelIndex, QModelIndex)), this, SLOT(currentChanged(QModelIndex, QModelIndex)));
 	if (!dontEmitDiveChangedSignal)
-		emit currentDiveChanged();
+		emit diveListNotifier.selectionChanged();
+
+	// Display the new, processed, selection
+	QTreeView::selectionChanged(selectionModel()->selection(), newDeselected);
 }
 
 enum asked_user {NOTYET, MERGE, DONTMERGE};