Mobile: replace model-reset by row-addition in DiveListModel::reload()

Owing to apparent QML breakage, a model-reset leads to the DiveDetail
page being reloaded for every dive in the list(!). Therefore, add
rows instead.

This leads to extremely subtle code, as it is now imperative that
the model has been properly cleared beforehand. Nevertheless, for
now we have to do this to fix a severe performance regression.

Fixes #2295

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

2 files changed, 12 insertions, 4 deletions

diff --git a/qt-models/divelistmodel.cpp b/qt-models/divelistmodel.cpp
index 6f7d69412..9aa78f344 100644
--- a/qt-models/divelistmodel.cpp
+++ b/qt-models/divelistmodel.cpp
@@ -73,7 +73,7 @@ int DiveListSortModel::getIdxForId(int id)
 void DiveListSortModel::reload()
 {
 	DiveListModel *mySourceModel = qobject_cast<DiveListModel *>(sourceModel());
-	mySourceModel->reload();
+	mySourceModel->resetInternalData();
 }
 
 // In QtQuick ListView, section headings can only be strings. To identify dives
@@ -180,8 +180,16 @@ void DiveListModel::clear()
 
 void DiveListModel::reload()
 {
-	beginResetModel();
-	endResetModel();
+	// Note: instead of doing a (logical) beginResetModel()/endResetModel(),
+	// we add the rows (if any). The reason is that a beginResetModel()/endResetModel()
+	// pair resulted in the DiveDetailsPage being renedered for *every* dive in
+	// the list. It is unclear whether this is a Qt-bug or intended insanity.
+	// Therefore, this function must only be called after having called clear().
+	// Otherwise the model will become inconsistent!
+	if (dive_table.nr > 0) {
+		beginInsertRows(QModelIndex(), 0, dive_table.nr - 1);
+		endInsertRows();
+	}
 }
 
 void DiveListModel::resetInternalData()
diff --git a/qt-models/divelistmodel.h b/qt-models/divelistmodel.h
index 686dcd1c3..19838f468 100644
--- a/qt-models/divelistmodel.h
+++ b/qt-models/divelistmodel.h
@@ -53,7 +53,7 @@ public:
 	void removeDive(int i);
 	void removeDiveById(int id);
 	void updateDive(int i, dive *d);
-	void reload();
+	void reload(); // Only call after clearing the model!
 	struct dive *getDive(int i);
 	int rowCount(const QModelIndex &parent = QModelIndex()) const;
 	int getDiveIdx(int id) const;