Fix NPE in v7 compatibility Grid during datasource rebind (#11473)

Add DataChangeHandler removal in v7 Grid just as in v8 Grid.
Adding tests to the fix to verify, that NPE is not thrown.

1 files changed, 5 insertions, 3 deletions

diff --git a/compatibility-client/src/main/java/com/vaadin/v7/client/widgets/Grid.java b/compatibility-client/src/main/java/com/vaadin/v7/client/widgets/Grid.java
index 631f3bdb65..1d2f88f570 100755
--- a/compatibility-client/src/main/java/com/vaadin/v7/client/widgets/Grid.java
+++ b/compatibility-client/src/main/java/com/vaadin/v7/client/widgets/Grid.java
@@ -4152,6 +4152,7 @@ public class Grid<T> extends ResizeComposite implements HasSelectionHandlers<T>,
      * on initialization, but not after that.
      */
     private DataSource<T> dataSource;
+    private Registration changeHandler;
 
     /**
      * Currently available row range in DataSource.
@@ -7023,12 +7024,13 @@ public class Grid<T> extends ResizeComposite implements HasSelectionHandlers<T>,
 
         selectionModel.reset();
 
-        if (this.dataSource != null) {
-            this.dataSource.addDataChangeHandler((DataChangeHandler) null);
+        if (changeHandler != null) {
+            changeHandler.remove();
+            changeHandler = null;
         }
 
         this.dataSource = dataSource;
-        dataSource.addDataChangeHandler(new DataChangeHandler() {
+		changeHandler = dataSource.addDataChangeHandler(new DataChangeHandler() {
                     @Override
                     public void dataUpdated(int firstIndex, int numberOfItems) {
                         escalator.getBody().refreshRows(firstIndex, numberOfItems);