Always calculate Escalator max row count the same way (#8740)

* Rename getMaxEscalatorRowCapacity to describe what it does

* Always calculate Escalator max row count the same way

This changes Escalator to not take a horizontal scrollbar
into account when trying to determine "maximum visible rows". This will
add another row, compared to previous versions, when there is a horizontal
scrollbar. In reality, it would likely make sense to always add 10 more rows
to have some buffer above and below the visible area.

Fixes #8661

1 files changed, 19 insertions, 13 deletions

diff --git a/client/src/main/java/com/vaadin/client/widgets/Escalator.java b/client/src/main/java/com/vaadin/client/widgets/Escalator.java
index f9c8d96ad4..7d5cd8981b 100644
--- a/client/src/main/java/com/vaadin/client/widgets/Escalator.java
+++ b/client/src/main/java/com/vaadin/client/widgets/Escalator.java
@@ -2999,7 +2999,7 @@ public class Escalator extends Widget
         private List<TableRowElement> fillAndPopulateEscalatorRowsIfNeeded(
                 final int index, final int numberOfRows) {
 
-            final int escalatorRowsStillFit = getMaxEscalatorRowCapacity()
+            final int escalatorRowsStillFit = getMaxVisibleRowCount()
                     - getDomRowCount();
             final int escalatorRowsNeeded = Math.min(numberOfRows,
                     escalatorRowsStillFit);
@@ -3032,16 +3032,22 @@ public class Escalator extends Widget
             }
         }
 
-        private int getMaxEscalatorRowCapacity() {
-            final int maxEscalatorRowCapacity = (int) Math
-                    .ceil(getHeightOfSection() / getDefaultRowHeight()) + 1;
+        private int getMaxVisibleRowCount() {
+            double heightOfSection = getHeightOfSection();
+            // By including the possibly shown scrollbar height, we get a
+            // consistent count and do not add/remove rows whenever a scrollbar
+            // is shown
+            heightOfSection += horizontalScrollbarDeco.getOffsetHeight();
+            double defaultRowHeight = getDefaultRowHeight();
+            final int maxVisibleRowCount = (int) Math
+                    .ceil(heightOfSection / defaultRowHeight) + 1;
 
             /*
-             * maxEscalatorRowCapacity can become negative if the headers and
-             * footers start to overlap. This is a crazy situation, but Vaadin
-             * blinks the components a lot, so it's feasible.
+             * maxVisibleRowCount can become negative if the headers and footers
+             * start to overlap. This is a crazy situation, but Vaadin blinks
+             * the components a lot, so it's feasible.
              */
-            return Math.max(0, maxEscalatorRowCapacity);
+            return Math.max(0, maxVisibleRowCount);
         }
 
         @Override
@@ -3524,12 +3530,12 @@ public class Escalator extends Widget
              * TODO [[spacer]]: these assumptions will be totally broken with
              * spacers.
              */
-            final int maxEscalatorRows = getMaxEscalatorRowCapacity();
+            final int maxVisibleRowCount = getMaxVisibleRowCount();
             final int currentTopRowIndex = getLogicalRowIndex(
                     visualRowOrder.getFirst());
 
             final Range[] partitions = logicalRange.partitionWith(
-                    Range.withLength(currentTopRowIndex, maxEscalatorRows));
+                    Range.withLength(currentTopRowIndex, maxVisibleRowCount));
             final Range insideRange = partitions[1];
             return insideRange.offsetBy(-currentTopRowIndex);
         }
@@ -3641,8 +3647,8 @@ public class Escalator extends Widget
                 return;
             }
 
-            final int maxEscalatorRows = getMaxEscalatorRowCapacity();
-            final int neededEscalatorRows = Math.min(maxEscalatorRows,
+            final int maxVisibleRowCount = getMaxVisibleRowCount();
+            final int neededEscalatorRows = Math.min(maxVisibleRowCount,
                     body.getRowCount());
             final int neededEscalatorRowsDiff = neededEscalatorRows
                     - visualRowOrder.size();
@@ -6687,7 +6693,7 @@ public class Escalator extends Widget
      * @return the maximum capacity
      */
     public int getMaxVisibleRowCount() {
-        return body.getMaxEscalatorRowCapacity();
+        return body.getMaxVisibleRowCount();
     }
 
     /**