Make CheckBoxGroup.SimpleMultiSelectModel return a selection copy #293.

getSelectedItems() must return a copy to fulfill the contract specified 
in SelectionModel: it must be a snapshot of the current state and safe
to iterate over while changing selection.

Change-Id: Ie2f15eb626dd80df2036bcb2d4e9387fc31389c9

2 files changed, 15 insertions, 1 deletions

diff --git a/server/src/main/java/com/vaadin/ui/CheckBoxGroup.java b/server/src/main/java/com/vaadin/ui/CheckBoxGroup.java
index 8525dc6cbb..d5b2c5a851 100644
--- a/server/src/main/java/com/vaadin/ui/CheckBoxGroup.java
+++ b/server/src/main/java/com/vaadin/ui/CheckBoxGroup.java
@@ -71,7 +71,7 @@ public class CheckBoxGroup<T> extends AbstractMultiSelect<T> {
 
         @Override
         public Set<T> getSelectedItems() {
-            return Collections.unmodifiableSet(selection);
+            return Collections.unmodifiableSet(new LinkedHashSet<>(selection));
         }
 
         @Override
diff --git a/server/src/test/java/com/vaadin/data/BinderMultiSelectTest.java b/server/src/test/java/com/vaadin/data/BinderMultiSelectTest.java
index 93f4ccdac4..fd75c930f3 100644
--- a/server/src/test/java/com/vaadin/data/BinderMultiSelectTest.java
+++ b/server/src/test/java/com/vaadin/data/BinderMultiSelectTest.java
@@ -118,6 +118,20 @@ public class BinderMultiSelectTest
     }
 
     @Test
+    public void bound_setSelection_beanValueIsACopy() {
+        bindEnum();
+
+        select.select(TestEnum.TWO);
+
+        Set<TestEnum> enums = item.getEnums();
+
+        binder.bind(new BeanWithEnums());
+        select.select(TestEnum.ONE);
+
+        assertEquals(Collections.singleton(TestEnum.TWO), enums);
+    }
+
+    @Test
     public void bound_deselect_beanValueUpdatedToNull() {
         item.setEnums(Collections.singleton(TestEnum.ONE));
         bindEnum();