Fix Grid DetailsGenerator being removed on Container change (#19593)

Change-Id: Ied328804260b1a7bb35093fca1d972735559cf41

server/src/com/vaadin/ui/Grid.java

@@ -312,7 +312,7 @@ public class Grid extends AbstractFocusable implements SelectionNotifier,
          * 
          * @see #setDetailsGenerator(DetailsGenerator)
          */
-        private DetailsGenerator detailsGenerator = DetailsGenerator.NULL;
+        private DetailsGenerator detailsGenerator;
 
         /**
          * This map represents all details that are currently visible on the
@@ -334,7 +334,13 @@ public class Grid extends AbstractFocusable implements SelectionNotifier,
         private final Set<Object> openDetails = new HashSet<Object>();
 
         public DetailComponentManager(Grid grid) {
+            this(grid, DetailsGenerator.NULL);
+        }
+
+        public DetailComponentManager(Grid grid,
+                DetailsGenerator detailsGenerator) {
             super(grid);
+            setDetailsGenerator(detailsGenerator);
         }
 
         /**
@@ -4914,7 +4920,12 @@ public class Grid extends AbstractFocusable implements SelectionNotifier,
             }
         }
 
-        detailComponentManager = new DetailComponentManager(this);
+        if (detailComponentManager != null) {
+            detailComponentManager = new DetailComponentManager(this,
+                    detailComponentManager.getDetailsGenerator());
+        } else {
+            detailComponentManager = new DetailComponentManager(this);
+        }
 
         /*
          * selectionModel == null when the invocation comes from the

server/tests/src/com/vaadin/tests/server/component/grid/GridContainerTest.java

@@ -19,10 +19,32 @@ import org.junit.Assert;
 import org.junit.Test;
 
 import com.vaadin.data.util.IndexedContainer;
+import com.vaadin.ui.Component;
 import com.vaadin.ui.Grid;
+import com.vaadin.ui.Grid.DetailsGenerator;
+import com.vaadin.ui.Grid.RowReference;
+import com.vaadin.ui.Label;
 
 public class GridContainerTest {
 
+    @Test
+    public void testDetailsGeneratorDoesNotResetOnContainerChange() {
+        Grid grid = new Grid();
+        DetailsGenerator detGen = new DetailsGenerator() {
+
+            @Override
+            public Component getDetails(RowReference rowReference) {
+                return new Label("Empty details");
+            }
+        };
+        grid.setDetailsGenerator(detGen);
+
+        grid.setContainerDataSource(createContainer());
+
+        Assert.assertEquals("DetailsGenerator changed", detGen,
+                grid.getDetailsGenerator());
+    }
+
     @Test
     public void testSetContainerTwice() throws Exception {