Fix a layout bug caused by a delegate item that was moved by the user5.13

The position of the first item in the list of visualItems was used to
know how to layout the rest of the visual items.
However, this did not work if the first item was actually moved (e.g.
due to a DnD operation). We therefore store the position of the first
visual item after each time we arrange it, and use that as a basis on
where to start layouting from.

Task-number: QTBUG-78076
Change-Id: I837f5b7d61a13d98d23287685c6fd66817360906
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

3 files changed, 12 insertions, 1 deletions

diff --git a/src/quick/items/qquickitemview.cpp b/src/quick/items/qquickitemview.cpp
index 120eeb13d5..370ecee01d 100644
--- a/src/quick/items/qquickitemview.cpp
+++ b/src/quick/items/qquickitemview.cpp
@@ -1784,6 +1784,7 @@ void QQuickItemViewPrivate::refill(qreal from, qreal to)
         if (prevCount != itemCount)
             emit q->countChanged();
     } while (currentChanges.hasPendingChanges() || bufferedChanges.hasPendingChanges());
+    storeFirstVisibleItemPosition();
 }
 
 void QQuickItemViewPrivate::regenerate(bool orientationChanged)
@@ -1870,6 +1871,7 @@ void QQuickItemViewPrivate::layout()
 
     updateSections();
     layoutVisibleItems();
+    storeFirstVisibleItemPosition();
 
     int lastIndexInView = findLastIndexInView();
     refill();
@@ -1954,7 +1956,7 @@ 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;
@@ -2000,6 +2002,7 @@ bool QQuickItemViewPrivate::applyModelChanges(ChangeResult *totalInsertionResult
         if (!insertions.isEmpty()) {
             repositionFirstItem(prevVisibleItemsFirst, prevVisibleItemsFirstPos, prevFirstItemInView, &insertionResult, &removalResult);
             layoutVisibleItems(removals.first().index);
+            storeFirstVisibleItemPosition();
         }
     }
 
@@ -2020,6 +2023,7 @@ 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 1f42c847b3..325b91d190 100644
--- a/src/quick/items/qquickitemview_p_p.h
+++ b/src/quick/items/qquickitemview_p_p.h
@@ -258,6 +258,12 @@ 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 8b70ffd0d7..ebae4d14ea 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);