Repopulate the GridLayout if flow is changed

This is needed because changing the flow will change which
cell an item is associated with.

Change-Id: Id84d1710fb6d7debe72a859c52b505e1e47f06b0
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@digia.com>

src/layouts/qquicklinearlayout.cpp

@@ -515,7 +515,8 @@ void QQuickGridLayout::setFlow(QQuickGridLayout::Flow flow)
     if (d->flow == flow)
         return;
     d->flow = flow;
-    invalidate();
+    // If flow is changed, the layout needs to be repopulated
+    updateLayoutItems();
     emit flowChanged();
 }
 

tests/auto/controls/data/tst_gridlayout.qml

@@ -58,6 +58,46 @@ Item {
             return [item.x, item.y, item.width, item.height];
         }
 
+        Component {
+            id: layout_flow_Component
+            GridLayout {
+                columns: 4
+                columnSpacing: 0
+                rowSpacing: 0
+                Repeater {
+                    model: 6
+                    Rectangle {
+                        color: "red"
+                        Layout.preferredWidth: 10
+                        Layout.preferredHeight: 10
+                        Text { text: index }
+                    }
+                }
+            }
+        }
+
+        function test_flow()
+        {
+            var layout = layout_flow_Component.createObject(container);
+            compare(itemRect(layout.children[0]), [ 0,  0, 10, 10])
+            compare(itemRect(layout.children[1]), [10,  0, 10, 10])
+            compare(itemRect(layout.children[2]), [20,  0, 10, 10])
+            compare(itemRect(layout.children[3]), [30,  0, 10, 10])
+
+            compare(itemRect(layout.children[4]), [ 0, 10, 10, 10])
+            compare(itemRect(layout.children[5]), [10, 10, 10, 10])
+
+            layout.rows = 4
+            layout.flow = GridLayout.TopToBottom
+            compare(itemRect(layout.children[0]), [ 0,  0, 10, 10])
+            compare(itemRect(layout.children[1]), [ 0, 10, 10, 10])
+            compare(itemRect(layout.children[2]), [ 0, 20, 10, 10])
+            compare(itemRect(layout.children[3]), [ 0, 30, 10, 10])
+
+            compare(itemRect(layout.children[4]), [10,  0, 10, 10])
+            compare(itemRect(layout.children[5]), [10, 10, 10, 10])
+        }
+
         Component {
             id: layout_flowLeftToRight_Component
             GridLayout {