When a DelegateModel delegate changes, refill the view

It looked a bit odd that the DelegateModel delegate property was not a
notifying property.  Adding the delegateChanged signal makes it easier
to update the view when this happens.  The previous approach of removing
all delegates and adding all new ones resulted in the view losing its
currentIndex and often scrolling to a different place.  It's also nice
to reduce the number of d-> indirections by adding the
QQuickItemViewPrivate::applyDelegateChange() function, so that we just
need one indirection to call it, and then it updates all the internal
stuff in one place.

Done-with: Frederik Gladhorn
Done-with: Joni Poikelin
Fixes: QTBUG-63477
Change-Id: I2d17fd11ff4a2fcb20968a7182dd2c403abb715a
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

1 files changed, 22 insertions, 16 deletions

diff --git a/src/quick/items/qquickitemview.cpp b/src/quick/items/qquickitemview.cpp
index bbfbf6244c..e1af65c986 100644
--- a/src/quick/items/qquickitemview.cpp
+++ b/src/quick/items/qquickitemview.cpp
@@ -247,6 +247,8 @@ void QQuickItemView::setModel(const QVariant &m)
 
         connect(d->model, SIGNAL(modelUpdated(QQmlChangeSet,bool)),
                 this, SLOT(modelUpdated(QQmlChangeSet,bool)));
+        if (QQmlDelegateModel *dataModel = qobject_cast<QQmlDelegateModel*>(d->model))
+            QObjectPrivate::connect(dataModel, &QQmlDelegateModel::delegateChanged, d, &QQuickItemViewPrivate::applyDelegateChange);
         emit countChanged();
     }
     emit modelChanged();
@@ -277,22 +279,8 @@ void QQuickItemView::setDelegate(QQmlComponent *delegate)
     if (QQmlDelegateModel *dataModel = qobject_cast<QQmlDelegateModel*>(d->model)) {
         int oldCount = dataModel->count();
         dataModel->setDelegate(delegate);
-        if (isComponentComplete()) {
-            d->releaseVisibleItems();
-            d->releaseItem(d->currentItem);
-            d->currentItem = nullptr;
-            d->updateSectionCriteria();
-            d->refill();
-            d->moveReason = QQuickItemViewPrivate::SetIndex;
-            d->updateCurrent(d->currentIndex);
-            if (d->highlight && d->currentItem) {
-                if (d->autoHighlight)
-                    d->resetHighlightPosition();
-                d->updateTrackedItem();
-            }
-            d->moveReason = QQuickItemViewPrivate::Other;
-            d->updateViewport();
-        }
+        if (isComponentComplete())
+            d->applyDelegateChange();
         if (oldCount != dataModel->count())
             emit countChanged();
     }
@@ -1089,6 +1077,24 @@ qreal QQuickItemViewPrivate::calculatedMaxExtent() const
     return maxExtent;
 }
 
+void QQuickItemViewPrivate::applyDelegateChange()
+{
+    releaseVisibleItems();
+    releaseItem(currentItem);
+    currentItem = nullptr;
+    updateSectionCriteria();
+    refill();
+    moveReason = QQuickItemViewPrivate::SetIndex;
+    updateCurrent(currentIndex);
+    if (highlight && currentItem) {
+        if (autoHighlight)
+            resetHighlightPosition();
+        updateTrackedItem();
+    }
+    moveReason = QQuickItemViewPrivate::Other;
+    updateViewport();
+}
+
 // for debugging only
 void QQuickItemViewPrivate::checkVisible() const
 {