From 142367bd4cd21c604741c098b03c49e712e85a75 Mon Sep 17 00:00:00 2001
From: Mathieu Pellerin <nirvn.asia@gmail.com>
Date: Sun, 14 Jan 2024 10:24:21 +0700
Subject: [PATCH] When opening or reloading a project, clear the previous one
 to empty the layer tree

---
 src/core/layertreemodel.cpp | 23 ++++++++++++++++++++---
 src/core/layertreemodel.h   |  3 ++-
 src/core/qgismobileapp.cpp  |  7 +++++--
 src/qml/qgismobileapp.qml   |  4 ++--
 4 files changed, 29 insertions(+), 8 deletions(-)

diff --git a/src/core/layertreemodel.cpp b/src/core/layertreemodel.cpp
index 7a80a7418c..f12a10d6f5 100644
--- a/src/core/layertreemodel.cpp
+++ b/src/core/layertreemodel.cpp
@@ -115,7 +115,8 @@ FlatLayerTreeModelBase::FlatLayerTreeModelBase( QgsLayerTree *layerTree, QgsProj
   mLayerTreeModel = new QgsLayerTreeModel( layerTree, this );
   mLayerTreeModel->setFlag( QgsLayerTreeModel::ShowLegendAsTree, true );
   QAbstractProxyModel::setSourceModel( mLayerTreeModel );
-  connect( mProject, &QgsProject::cleared, this, [=] { updateTemporalState(); buildMap( nullptr ); } );
+  connect( mProject, &QgsProject::aboutToBeCleared, this, [=] { mFrozen++; clearMap(); } );
+  connect( mProject, &QgsProject::cleared, this, [=] { mFrozen--; } );
   connect( mProject, &QgsProject::readProject, this, [=] { buildMap( mLayerTreeModel ); } );
   connect( mProject, &QgsProject::layersAdded, this, &FlatLayerTreeModelBase::adjustTemporalStateFromAddedLayers );
   connect( mLayerTreeModel, &QAbstractItemModel::dataChanged, this, &FlatLayerTreeModelBase::updateMap );
@@ -125,12 +126,12 @@ FlatLayerTreeModelBase::FlatLayerTreeModelBase( QgsLayerTree *layerTree, QgsProj
 
 void FlatLayerTreeModelBase::freeze()
 {
-  mFrozen = true;
+  mFrozen++;
 }
 
 void FlatLayerTreeModelBase::unfreeze( bool resetModel )
 {
-  mFrozen = false;
+  mFrozen = 0;
   if ( resetModel )
     buildMap( mLayerTreeModel );
 }
@@ -331,6 +332,22 @@ void FlatLayerTreeModelBase::removeFromMap( const QModelIndex &parent, int first
   }
 }
 
+void FlatLayerTreeModelBase::clearMap()
+{
+  if ( mIsTemporal )
+  {
+    mIsTemporal = false;
+    emit isTemporalChanged();
+  }
+
+  beginResetModel();
+  mRowMap.clear();
+  mIndexMap.clear();
+  mCollapsedItems.clear();
+  mTreeLevelMap.clear();
+  endResetModel();
+}
+
 int FlatLayerTreeModelBase::buildMap( QgsLayerTreeModel *model, const QModelIndex &parent, int row, int treeLevel )
 {
   if ( mFrozen )
diff --git a/src/core/layertreemodel.h b/src/core/layertreemodel.h
index ec60fd3ab6..cd95539c10 100644
--- a/src/core/layertreemodel.h
+++ b/src/core/layertreemodel.h
@@ -34,6 +34,7 @@ class FlatLayerTreeModelBase : public QAbstractProxyModel
 
     void updateMap( const QModelIndex &topLeft, const QModelIndex &bottomRight, const QVector<int> &roles );
     int buildMap( QgsLayerTreeModel *model, const QModelIndex &parent = QModelIndex(), int row = 0, int treeLevel = 0 );
+    void clearMap();
 
     void removeFromMap( const QModelIndex &parent, int first, int last );
     void insertInMap( const QModelIndex &parent, int first, int last );
@@ -101,7 +102,7 @@ class FlatLayerTreeModelBase : public QAbstractProxyModel
 
     bool mIsTemporal = false;
 
-    bool mFrozen = false;
+    int mFrozen = 0;
 };
 
 class FlatLayerTreeModel : public QSortFilterProxyModel
diff --git a/src/core/qgismobileapp.cpp b/src/core/qgismobileapp.cpp
index 862cb440e0..5fcc456d47 100644
--- a/src/core/qgismobileapp.cpp
+++ b/src/core/qgismobileapp.cpp
@@ -687,6 +687,8 @@ bool QgisMobileapp::loadProjectFile( const QString &path, const QString &name )
 
     mAuthRequestHandler->clearStoredRealms();
 
+    // Clear project to empty the layer tree prior to freezing during project load
+    mProject->clear();
     mProjectFilePath = path;
     mProjectFileName = !name.isEmpty() ? name : fi.completeBaseName();
 
@@ -702,6 +704,9 @@ void QgisMobileapp::reloadProjectFile()
   if ( mProjectFilePath.isEmpty() )
     QgsMessageLog::logMessage( tr( "No project file currently opened" ), QStringLiteral( "QField" ), Qgis::Warning );
 
+  // Clear project to empty the layer tree prior to freezing during project load
+  mProject->clear();
+
   emit loadProjectTriggered( mProjectFilePath, mProjectFileName );
 }
 
@@ -715,8 +720,6 @@ void QgisMobileapp::readProjectFile()
 
   const QString suffix = fi.suffix().toLower();
 
-  mProject->removeAllMapLayers();
-  mProject->setTitle( QString() );
   mProject->layerTreeRegistryBridge()->setLayerInsertionMethod( Qgis::LayerTreeInsertionMethod::OptimalInInsertionGroup );
 
   mTrackingModel->reset();
diff --git a/src/qml/qgismobileapp.qml b/src/qml/qgismobileapp.qml
index 774e537d2d..909c7b300c 100644
--- a/src/qml/qgismobileapp.qml
+++ b/src/qml/qgismobileapp.qml
@@ -3206,9 +3206,9 @@ ApplicationWindow {
       busyOverlay.text = qsTr( "Loading %1" ).arg( name !== '' ? name : path )
       busyOverlay.state = "visible"
 
-      navigation.clearDestinationFeature();
+      navigation.clearDestinationFeature()
 
-      projectInfo.filePath = '';
+      projectInfo.filePath = ''
       readProjectTimer.start()
     }