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, 2 insertions, 1 deletions

diff --git a/src/qmlmodels/qqmldelegatemodel_p.h b/src/qmlmodels/qqmldelegatemodel_p.h
index 21eaef02e0..9e846ccc3e 100644
--- a/src/qmlmodels/qqmldelegatemodel_p.h
+++ b/src/qmlmodels/qqmldelegatemodel_p.h
@@ -77,7 +77,7 @@ class Q_QMLMODELS_PRIVATE_EXPORT QQmlDelegateModel : public QQmlInstanceModel, p
     Q_DECLARE_PRIVATE(QQmlDelegateModel)
 
     Q_PROPERTY(QVariant model READ model WRITE setModel)
-    Q_PROPERTY(QQmlComponent *delegate READ delegate WRITE setDelegate)
+    Q_PROPERTY(QQmlComponent *delegate READ delegate WRITE setDelegate NOTIFY delegateChanged)
     Q_PROPERTY(QString filterOnGroup READ filterGroup WRITE setFilterGroup NOTIFY filterGroupChanged RESET resetFilterGroup)
     Q_PROPERTY(QQmlDelegateModelGroup *items READ items CONSTANT) //TODO : worth renaming?
     Q_PROPERTY(QQmlDelegateModelGroup *persistedItems READ persistedItems CONSTANT)
@@ -136,6 +136,7 @@ Q_SIGNALS:
     void filterGroupChanged();
     void defaultGroupsChanged();
     void rootIndexChanged();
+    void delegateChanged();
 
 private Q_SLOTS:
     void _q_itemsChanged(int index, int count, const QVector<int> &roles);