8251941: ListCell: visual artifact when items contain null values

Reviewed-by: aghaisas

Author: Jeanette Winzenburg

modules/javafx.controls/src/main/java/javafx/scene/control/ListCell.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2010, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2010, 2020, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -483,7 +483,7 @@ private void updateItem(int oldIndex) {
             // refer to Ensemble8PopUpTree.png - in this case the arrows are being
             // shown as the new cells are instantiated with the arrows in the
             // children list, and are only hidden in updateItem.
-            if ((!isEmpty && oldValue != null) || firstRun) {
+            if (!isEmpty || firstRun) {
                 updateItem(null, true);
                 firstRun = false;
             }

modules/javafx.controls/src/test/java/test/javafx/scene/control/ListCellTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2011, 2016, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2011, 2020, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -277,6 +277,93 @@ public class ListCellTest {
         assertEquals("Water", cell.getItem());
     }
 
+//---------- tests around JDK-8251941: broken cleanup with null item
+
+    /**
+     * Transition not-empty -> empty by items modification
+     */
+    @Test
+    public void testNullItemRemoveAsLast() {
+        model.add(null);
+        cell.updateListView(list);
+        int last = model.size() - 1;
+        cell.updateIndex(last);
+        model.remove(last);
+        assertOffRangeState(last);
+    }
+
+    /**
+     * Sanity: transition not-empty -> not empty by items modification
+     */
+    @Test
+    public void testNullItemRemoveAsFirst() {
+        int first = 0;
+        model.add(first, null);
+        cell.updateListView(list);
+        cell.updateIndex(first);
+        model.remove(first);
+        assertInRangeState(first);
+    }
+
+    /**
+     * Transition not-empty -> empty by updateIndex
+     */
+    @Test
+    public void testNullItemUpdateIndexOffRange() {
+        model.add(0, null);
+        cell.updateListView(list);
+        cell.updateIndex(0);
+        // update to off range > max
+        cell.updateIndex(model.size());
+        assertOffRangeState(model.size());
+    }
+
+    /**
+     * Transition not-empty -> empty by updateIndex
+     */
+    @Test
+    public void testNullItemUpdateIndexNegative() {
+        model.add(0, null);
+        cell.updateListView(list);
+        cell.updateIndex(0);
+        // update to off range < 0
+        cell.updateIndex(-1);
+        assertOffRangeState(-1);
+    }
+
+    /**
+     * Sanity: in-range null item.
+     */
+    @Test
+    public void testNullItem() {
+        // null item in range, verify state
+        model.add(0, null);
+        cell.updateListView(list);
+        cell.updateIndex(0);
+        assertInRangeState(0);
+    }
+
+    /**
+     * Asserts state for the given off-range index.
+     * @param index
+     */
+    protected void assertOffRangeState(int index) {
+        assertEquals("off range index", index, cell.getIndex());
+        assertNull("off range cell item must be null", cell.getItem());
+        assertTrue("off range cell must be empty", cell.isEmpty());
+    }
+
+    /**
+     * Asserts state for the given in-range index.
+     * @param index
+     */
+    protected void assertInRangeState(int index) {
+        assertEquals("in range index", index, cell.getIndex());
+        assertEquals("in range cell item must be same as model item", model.get(index), cell.getItem());
+        assertFalse("in range cell must not be empty", cell.isEmpty());
+    }
+
+
     /*********************************************************************
      * Tests for the selection listener                                  *
      ********************************************************************/