Prevent scroll position reset on GridLayout hierarchy change (#13386)

State change handling by default clears measured size if the size is set
to undefined; this would cause GridLayout to shrink to zero size because
its child cells have position: absolute. The layout phase recomputes the
size, but in some cases the browser reflows first, affecting the scroll
position of the layout parent. This patch prevents GridLayout from
clearing once-computed sizes during state change.

Change-Id: Id6e066c3ea360083d16d3fcc5c6d7d4bb6cea8b7

2 files changed, 41 insertions, 2 deletions

diff --git a/client/src/com/vaadin/client/ui/AbstractComponentConnector.java b/client/src/com/vaadin/client/ui/AbstractComponentConnector.java
index f6c26cda05..47140348f9 100644
--- a/client/src/com/vaadin/client/ui/AbstractComponentConnector.java
+++ b/client/src/com/vaadin/client/ui/AbstractComponentConnector.java
@@ -217,11 +217,24 @@ public abstract class AbstractComponentConnector extends AbstractConnector
 
     }
 
+    /**
+     * Updates the component size based on the shared state, invoking the
+     * {@link LayoutManager layout manager} if necessary.
+     */
     protected void updateComponentSize() {
         updateComponentSize(getState().width == null ? "" : getState().width,
                 getState().height == null ? "" : getState().height);
     }
 
+    /**
+     * Updates the component size, invoking the {@link LayoutManager layout
+     * manager} if necessary.
+     * 
+     * @param newWidth
+     *            The new width as a CSS string. Cannot be null.
+     * @param newHeight
+     *            The new height as a CSS string. Cannot be null.
+     */
     protected void updateComponentSize(String newWidth, String newHeight) {
         Profiler.enter("AbstractComponentConnector.updateComponentSize");
 
@@ -255,13 +268,25 @@ public abstract class AbstractComponentConnector extends AbstractConnector
         Profiler.leave("AbstractComponentConnector.updateComponentSize update styleNames");
 
         Profiler.enter("AbstractComponentConnector.updateComponentSize update DOM");
-        widget.setHeight(newHeight);
-        widget.setWidth(newWidth);
+        updateWidgetSize(newWidth, newHeight);
         Profiler.leave("AbstractComponentConnector.updateComponentSize update DOM");
 
         Profiler.leave("AbstractComponentConnector.updateComponentSize");
     }
 
+    /**
+     * Updates the DOM size of this connector's {@link #getWidget() widget}.
+     * 
+     * @param newWidth
+     *            The new width as a CSS string. Cannot be null.
+     * @param newHeight
+     *            The new height as a CSS string. Cannot be null.
+     */
+    protected void updateWidgetSize(String newWidth, String newHeight) {
+        getWidget().setWidth(newWidth);
+        getWidget().setHeight(newHeight);
+    }
+
     @Override
     public boolean isRelativeHeight() {
         return ComponentStateUtil.isRelativeHeight(getState());
diff --git a/client/src/com/vaadin/client/ui/gridlayout/GridLayoutConnector.java b/client/src/com/vaadin/client/ui/gridlayout/GridLayoutConnector.java
index cc052fa6d5..c306282349 100644
--- a/client/src/com/vaadin/client/ui/gridlayout/GridLayoutConnector.java
+++ b/client/src/com/vaadin/client/ui/gridlayout/GridLayoutConnector.java
@@ -210,4 +210,18 @@ public class GridLayoutConnector extends AbstractComponentContainerConnector
     public void layoutHorizontally() {
         getWidget().updateWidth();
     }
+
+    @Override
+    protected void updateWidgetSize(String newWidth, String newHeight) {
+        // Prevent the element from momentarily shrinking to zero size
+        // when the size is set to undefined by a state change but before
+        // it is recomputed in the layout phase. This may affect scroll
+        // position in some cases; see #13386.
+        if (!isUndefinedHeight()) {
+            getWidget().setHeight(newHeight);
+        }
+        if (!isUndefinedWidth()) {
+            getWidget().setWidth(newWidth);
+        }
+    }
 }