Merge remote-tracking branch 'origin/5.13' into 5.14

Change-Id: I06578422b4558feabf7a77426b01e77953ab60e2

6 files changed, 67 insertions, 1 deletions

diff --git a/src/quick/doc/src/guidelines/qtquick-bestpractices.qdoc b/src/quick/doc/src/guidelines/qtquick-bestpractices.qdoc
index f4a1616943..abfff7cc11 100644
--- a/src/quick/doc/src/guidelines/qtquick-bestpractices.qdoc
+++ b/src/quick/doc/src/guidelines/qtquick-bestpractices.qdoc
@@ -402,6 +402,43 @@ property MyMenu optionsMenu
 For information on performance in QML and Qt Quick,
 see \l {Performance Considerations And Suggestions}.
 
+\section1 Prefer Declarative Bindings Over Imperative Assignments
+
+In QML, it's possible to use imperative JavaScript code to perform tasks
+such as responding to input events, send data over a network, and so on.
+Imperative code has an important place in QML, but it's also important
+to be aware of when not to use it.
+
+For example, consider the following imperative assignment:
+
+\code
+Rectangle {
+    Component.onCompleted: color = "red"
+}
+\endcode
+
+This has the following disadvantages:
+
+\list
+\li It's slow. The color property will first be evaluated with a
+    default-constructed value, and then again with "red" later on.
+\li It delays errors that could be found at build time to run time, slowing
+    down the development process.
+\li It overwrites any declarative binding that was in place. In most cases this
+    is intended, but sometimes it can be unintentional.
+    See \l {Debugging overwriting of bindings} for more information.
+\li It interferes with tooling; Qt Quick Designer, for example, doesn't support
+    JavaScript.
+\endlist
+
+The code can be rewritten to be a declarative binding instead:
+
+\code
+Rectangle {
+    color: "red"
+}
+\endcode
+
 \section1 Tools and Utilities
 
 For information on useful tools and utilies that make working with QML and
diff --git a/src/quick/items/qquickaccessibleattached.cpp b/src/quick/items/qquickaccessibleattached.cpp
index c150e4efa2..2da01e9151 100644
--- a/src/quick/items/qquickaccessibleattached.cpp
+++ b/src/quick/items/qquickaccessibleattached.cpp
@@ -433,6 +433,19 @@ void QQuickAccessibleAttached::setRole(QAccessible::Role role)
     }
 }
 
+bool QQuickAccessibleAttached::wasNameExplicitlySet() const
+{
+    return m_nameExplicitlySet;
+}
+
+// Allows types to attach an accessible name to an item as a convenience,
+// so long as the user hasn't done so themselves.
+void QQuickAccessibleAttached::setNameImplicitly(const QString &name)
+{
+    setName(name);
+    m_nameExplicitlySet = false;
+}
+
 QQuickAccessibleAttached *QQuickAccessibleAttached::qmlAttachedProperties(QObject *obj)
 {
     return new QQuickAccessibleAttached(obj);
diff --git a/src/quick/items/qquickaccessibleattached_p.h b/src/quick/items/qquickaccessibleattached_p.h
index f4194ef13d..87fb79ecc9 100644
--- a/src/quick/items/qquickaccessibleattached_p.h
+++ b/src/quick/items/qquickaccessibleattached_p.h
@@ -118,7 +118,10 @@ public:
             return QString();
         return m_name;
     }
+
+    bool wasNameExplicitlySet() const;
     void setName(const QString &name) {
+        m_nameExplicitlySet = true;
         if (name != m_name) {
             m_name = name;
             Q_EMIT nameChanged();
@@ -126,6 +129,7 @@ public:
             QAccessible::updateAccessibility(&ev);
         }
     }
+    void setNameImplicitly(const QString &name);
 
     QString description() const { return m_description; }
     void setDescription(const QString &description)
@@ -216,6 +220,7 @@ private:
     QAccessible::State m_state;
     QAccessible::State m_stateExplicitlySet;
     QString m_name;
+    bool m_nameExplicitlySet = false;
     QString m_description;
 
     static QMetaMethod sigPress;
diff --git a/src/quick/items/qquickitemview.cpp b/src/quick/items/qquickitemview.cpp
index 661f19509a..7c74eafd3a 100644
--- a/src/quick/items/qquickitemview.cpp
+++ b/src/quick/items/qquickitemview.cpp
@@ -1790,6 +1790,7 @@ void QQuickItemViewPrivate::refill(qreal from, qreal to)
         if (prevCount != itemCount)
             emit q->countChanged();
     } while (currentChanges.hasPendingChanges() || bufferedChanges.hasPendingChanges());
+    storeFirstVisibleItemPosition();
 }
 
 void QQuickItemViewPrivate::regenerate(bool orientationChanged)
@@ -1876,6 +1877,7 @@ void QQuickItemViewPrivate::layout()
 
     updateSections();
     layoutVisibleItems();
+    storeFirstVisibleItemPosition();
 
     int lastIndexInView = findLastIndexInView();
     refill();
@@ -1960,7 +1962,7 @@ bool QQuickItemViewPrivate::applyModelChanges(ChangeResult *totalInsertionResult
         prevFirstItemInViewPos = prevFirstItemInView->position();
         prevFirstItemInViewIndex = prevFirstItemInView->index;
     }
-    qreal prevVisibleItemsFirstPos = visibleItems.count() ? visibleItems.constFirst()->position() : 0.0;
+    qreal prevVisibleItemsFirstPos = visibleItems.count() ? firstVisibleItemPosition : 0.0;
 
     totalInsertionResult->visiblePos = prevFirstItemInViewPos;
     totalRemovalResult->visiblePos = prevFirstItemInViewPos;
@@ -2006,6 +2008,7 @@ bool QQuickItemViewPrivate::applyModelChanges(ChangeResult *totalInsertionResult
         if (!insertions.isEmpty()) {
             repositionFirstItem(prevVisibleItemsFirst, prevVisibleItemsFirstPos, prevFirstItemInView, &insertionResult, &removalResult);
             layoutVisibleItems(removals.first().index);
+            storeFirstVisibleItemPosition();
         }
     }
 
@@ -2026,6 +2029,7 @@ bool QQuickItemViewPrivate::applyModelChanges(ChangeResult *totalInsertionResult
         if (i < insertions.count() - 1) {
             repositionFirstItem(prevVisibleItemsFirst, prevVisibleItemsFirstPos, prevFirstItemInView, &insertionResult, &removalResult);
             layoutVisibleItems(insertions[i].index);
+            storeFirstVisibleItemPosition();
         }
         itemCount += insertions[i].count;
     }
diff --git a/src/quick/items/qquickitemview_p_p.h b/src/quick/items/qquickitemview_p_p.h
index 6442fee27d..b31f53b2c0 100644
--- a/src/quick/items/qquickitemview_p_p.h
+++ b/src/quick/items/qquickitemview_p_p.h
@@ -260,6 +260,12 @@ public:
     MovementReason moveReason;
 
     QList<FxViewItem *> visibleItems;
+    qreal firstVisibleItemPosition = 0;
+    void storeFirstVisibleItemPosition() {
+        if (!visibleItems.isEmpty()) {
+            firstVisibleItemPosition = visibleItems.constFirst()->position();
+        }
+    }
     int visibleIndex;
     int currentIndex;
     FxViewItem *currentItem;
diff --git a/src/quick/items/qquicklistview.cpp b/src/quick/items/qquicklistview.cpp
index 18a9afbad8..48bb70e597 100644
--- a/src/quick/items/qquicklistview.cpp
+++ b/src/quick/items/qquicklistview.cpp
@@ -805,6 +805,7 @@ void QQuickListViewPrivate::layoutVisibleItems(int fromModelIndex)
 
         FxViewItem *firstItem = *visibleItems.constBegin();
         bool fixedCurrent = currentItem && firstItem->item == currentItem->item;
+        firstVisibleItemPosition = firstItem->position();
         qreal sum = firstItem->size();
         qreal pos = firstItem->position() + firstItem->size() + spacing;
         firstItem->setVisible(firstItem->endPosition() >= from && firstItem->position() <= to);