8290331: Binding value left null when immediately revalidated in inva…

…lidation listener

Reviewed-by: mstrauss, kcr

modules/javafx.base/src/main/java/javafx/beans/binding/ObjectBinding.java

@@ -180,7 +180,15 @@ public final void invalidate() {
             valid = false;
             onInvalidating();
             ExpressionHelper.fireValueChangedEvent(helper);
-            value = null;  // clear cached value to avoid hard reference to stale data
+
+            /*
+             * Cached value should be cleared to avoid a strong reference to stale data,
+             * but only if this binding didn't become valid after firing the event:
+             */
+
+            if (!valid) {
+                value = null;
+            }
         }
     }
 

modules/javafx.base/src/test/java/test/javafx/beans/value/LazyObjectBindingTest.java

@@ -52,6 +52,24 @@ void shouldBeInvalidInitially() {
         assertFalse(binding.isValid());
     }
 
+    @Test
+    void invalidationWhichBecomesValidDuringCallbacksShouldReturnCorrectValue() {
+        LazyObjectBindingStub<String> binding = new LazyObjectBindingStub<>() {
+            @Override
+            protected String computeValue() {
+                return "A";
+            }
+        };
+
+        binding.addListener(obs -> {
+            assertEquals("A", binding.get());
+        });
+
+        binding.invalidate();  // becomes valid again immediately
+
+        assertEquals("A", binding.get());
+    }
+
     @Nested
     class WhenObservedWithInvalidationListener {
         private InvalidationListener invalidationListener = obs -> {};