Required properties: Break binding to model on write

This mirrors the behavior in other parts of QML where writing to a
property in imperative code breaks the binding.

Change-Id: Id19eef17a3c5e77bc4c2772bd749b38c732606a8
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

2 files changed, 36 insertions, 3 deletions

diff --git a/src/qmlmodels/qqmldelegatemodel.cpp b/src/qmlmodels/qqmldelegatemodel.cpp
index c37dc114a1..e2a750a43a 100644
--- a/src/qmlmodels/qqmldelegatemodel.cpp
+++ b/src/qmlmodels/qqmldelegatemodel.cpp
@@ -894,6 +894,7 @@ void PropertyUpdater::doUpdate()
     auto sender = QObject::sender();
     auto mo = sender->metaObject();
     auto signalIndex = QObject::senderSignalIndex();
+    ++updateCount;
     // start at 0 instead of propertyOffset to handle properties from parent hierarchy
     for (auto i = 0; i < mo->propertyCount() + mo->propertyOffset(); ++i) {
         auto property = mo->property(i);
@@ -907,6 +908,27 @@ void PropertyUpdater::doUpdate()
     }
 }
 
+void PropertyUpdater::breakBinding()
+{
+    auto it = senderToConnection.find(QObject::senderSignalIndex());
+    if (it == senderToConnection.end())
+        return;
+    if (updateCount == 0) {
+        QObject::disconnect(*it);
+        QQmlError warning;
+        warning.setUrl(qmlContext(QObject::sender())->baseUrl());
+        auto signalName = QString::fromLatin1(QObject::sender()->metaObject()->method(QObject::senderSignalIndex()).name());
+        signalName.chop(sizeof("changed")-1);
+        QString propName = signalName;
+        propName[0] = propName[0].toLower();
+        warning.setDescription(QString::fromUtf8("Writing to \"%1\" broke the binding to the underlying model").arg(propName));
+        qmlWarning(this, warning);
+        senderToConnection.erase(it);
+    } else {
+        --updateCount;
+    }
+}
+
 void QQDMIncubationTask::initializeRequiredProperties(QQmlDelegateModelItem *modelItemToIncubate, QObject *object)
 {
     auto incubatorPriv = QQmlIncubatorPrivate::get(this);
@@ -947,10 +969,18 @@ void QQDMIncubationTask::initializeRequiredProperties(QQmlDelegateModelItem *mod
                 // only write to property if it was actually requested by the component
                 if (wasInRequired && prop.hasNotifySignal()) {
                     QMetaMethod changeSignal = prop.notifySignal();
-                    QMetaMethod updateSlot = PropertyUpdater::staticMetaObject.method(PropertyUpdater::staticMetaObject.indexOfSlot("doUpdate()"));
-                    QObject::connect(modelItemToIncubate, changeSignal, updater, updateSlot);
+                    static QMetaMethod updateSlot = PropertyUpdater::staticMetaObject.method(PropertyUpdater::staticMetaObject.indexOfSlot("doUpdate()"));
+                    QMetaObject::Connection conn = QObject::connect(modelItemToIncubate, changeSignal, updater, updateSlot);
+                    auto propIdx = object->metaObject()->indexOfProperty(propName.toUtf8());
+                    QMetaMethod writeToPropSignal = object->metaObject()->property(propIdx).notifySignal();
+                    updater->senderToConnection[writeToPropSignal.methodIndex()] = conn;
+                    static QMetaMethod breakBinding = PropertyUpdater::staticMetaObject.method(PropertyUpdater::staticMetaObject.indexOfSlot("breakBinding()"));
+                    componentProp.write(prop.read(modelItemToIncubate));
+                    // the connection needs to established after the write,
+                    // else the signal gets triggered by it and breakBinding will remove the connection
+                    QObject::connect(object, writeToPropSignal, updater, breakBinding);
                 }
-                if (wasInRequired)
+                else if (wasInRequired) // we still have to write, even if there is no change signal
                     componentProp.write(prop.read(modelItemToIncubate));
             }
         }
diff --git a/src/qmlmodels/qqmldelegatemodel_p_p.h b/src/qmlmodels/qqmldelegatemodel_p_p.h
index f9dbc61a94..06365a212f 100644
--- a/src/qmlmodels/qqmldelegatemodel_p_p.h
+++ b/src/qmlmodels/qqmldelegatemodel_p_p.h
@@ -454,8 +454,11 @@ class PropertyUpdater : public QObject
 
 public:
     PropertyUpdater(QObject *parent);
+    QHash<int, QMetaObject::Connection> senderToConnection;
+    int updateCount = 0;
 public Q_SLOTS:
     void doUpdate();
+    void breakBinding();
 };
 
 QT_END_NAMESPACE