Refactor Html5 DnD feature based on API review (#9306)

* Refactor Html5 DnD client side based on API review

- Moved classes to "correct" packages.
- Removed method DragSourceExtension.clearDataTransferText()
- Remove ButtonDragSource in favor of more generic API

31 files changed, 244 insertions, 217 deletions

diff --git a/server/src/main/java/com/vaadin/event/Transferable.java b/server/src/main/java/com/vaadin/event/Transferable.java
index f75974a1cc..1f0ed866c1 100644
--- a/server/src/main/java/com/vaadin/event/Transferable.java
+++ b/server/src/main/java/com/vaadin/event/Transferable.java
@@ -18,9 +18,9 @@ package com.vaadin.event;
 import java.io.Serializable;
 import java.util.Collection;
 
-import com.vaadin.event.dnd.DragSourceExtension;
-import com.vaadin.event.dnd.DropEvent;
 import com.vaadin.ui.Component;
+import com.vaadin.ui.dnd.DragSourceExtension;
+import com.vaadin.ui.dnd.event.DropEvent;
 
 /**
  * Transferable wraps the data that is to be imported into another component.
diff --git a/server/src/main/java/com/vaadin/event/dd/DragAndDropEvent.java b/server/src/main/java/com/vaadin/event/dd/DragAndDropEvent.java
index 6f66036e5a..6bf8a7f319 100644
--- a/server/src/main/java/com/vaadin/event/dd/DragAndDropEvent.java
+++ b/server/src/main/java/com/vaadin/event/dd/DragAndDropEvent.java
@@ -19,7 +19,7 @@ import java.io.Serializable;
 
 import com.vaadin.event.Transferable;
 import com.vaadin.event.dd.acceptcriteria.AcceptCriterion;
-import com.vaadin.event.dnd.DropEvent;
+import com.vaadin.ui.dnd.event.DropEvent;
 
 /**
  * DragAndDropEvent wraps information related to drag and drop operation. It is
diff --git a/server/src/main/java/com/vaadin/event/dd/DragSource.java b/server/src/main/java/com/vaadin/event/dd/DragSource.java
index 8a3c8c32dc..6361925864 100644
--- a/server/src/main/java/com/vaadin/event/dd/DragSource.java
+++ b/server/src/main/java/com/vaadin/event/dd/DragSource.java
@@ -19,8 +19,8 @@ import java.util.Map;
 
 import com.vaadin.event.Transferable;
 import com.vaadin.event.dd.acceptcriteria.AcceptCriterion;
-import com.vaadin.event.dnd.DragSourceExtension;
 import com.vaadin.ui.Component;
+import com.vaadin.ui.dnd.DragSourceExtension;
 
 /**
  * DragSource is a {@link Component} that builds a {@link Transferable} for a
diff --git a/server/src/main/java/com/vaadin/event/dd/DropHandler.java b/server/src/main/java/com/vaadin/event/dd/DropHandler.java
index d6183940e9..a96b6206d5 100644
--- a/server/src/main/java/com/vaadin/event/dd/DropHandler.java
+++ b/server/src/main/java/com/vaadin/event/dd/DropHandler.java
@@ -21,7 +21,7 @@ import com.vaadin.event.Transferable;
 import com.vaadin.event.dd.acceptcriteria.AcceptAll;
 import com.vaadin.event.dd.acceptcriteria.AcceptCriterion;
 import com.vaadin.event.dd.acceptcriteria.ServerSideCriterion;
-import com.vaadin.event.dnd.DropListener;
+import com.vaadin.ui.dnd.event.DropListener;
 
 /**
  * DropHandlers contain the actual business logic for drag and drop operations.
diff --git a/server/src/main/java/com/vaadin/event/dd/DropTarget.java b/server/src/main/java/com/vaadin/event/dd/DropTarget.java
index 3d346418c0..5202718109 100644
--- a/server/src/main/java/com/vaadin/event/dd/DropTarget.java
+++ b/server/src/main/java/com/vaadin/event/dd/DropTarget.java
@@ -17,8 +17,8 @@ package com.vaadin.event.dd;
 
 import java.util.Map;
 
-import com.vaadin.event.dnd.DropTargetExtension;
 import com.vaadin.ui.Component;
+import com.vaadin.ui.dnd.DropTargetExtension;
 
 /**
  * DropTarget is an interface for components supporting drop operations. A
diff --git a/server/src/main/java/com/vaadin/event/dd/TargetDetails.java b/server/src/main/java/com/vaadin/event/dd/TargetDetails.java
index 4a22958952..710fc5792f 100644
--- a/server/src/main/java/com/vaadin/event/dd/TargetDetails.java
+++ b/server/src/main/java/com/vaadin/event/dd/TargetDetails.java
@@ -17,7 +17,7 @@ package com.vaadin.event.dd;
 
 import java.io.Serializable;
 
-import com.vaadin.event.dnd.DropEvent;
+import com.vaadin.ui.dnd.event.DropEvent;
 
 /**
  * TargetDetails wraps drop target related information about
diff --git a/server/src/main/java/com/vaadin/event/dd/TargetDetailsImpl.java b/server/src/main/java/com/vaadin/event/dd/TargetDetailsImpl.java
index fadc1877cf..3ede6a20e0 100644
--- a/server/src/main/java/com/vaadin/event/dd/TargetDetailsImpl.java
+++ b/server/src/main/java/com/vaadin/event/dd/TargetDetailsImpl.java
@@ -18,8 +18,8 @@ package com.vaadin.event.dd;
 import java.util.HashMap;
 import java.util.Map;
 
-import com.vaadin.event.dnd.DropEvent;
 import com.vaadin.shared.MouseEventDetails;
+import com.vaadin.ui.dnd.event.DropEvent;
 
 /**
  * A HashMap backed implementation of {@link TargetDetails} for terminal
diff --git a/server/src/main/java/com/vaadin/event/dnd/ButtonDragSource.java b/server/src/main/java/com/vaadin/event/dnd/ButtonDragSource.java
deleted file mode 100644
index 3d0d93dfa2..0000000000
--- a/server/src/main/java/com/vaadin/event/dnd/ButtonDragSource.java
+++ /dev/null
@@ -1,44 +0,0 @@
-/*
- * Copyright 2000-2016 Vaadin Ltd.
- *
- * Licensed under the Apache License, Version 2.0 (the "License"); you may not
- * use this file except in compliance with the License. You may obtain a copy of
- * the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
- * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
- * License for the specific language governing permissions and limitations under
- * the License.
- */
-package com.vaadin.event.dnd;
-
-import com.vaadin.annotations.Widgetset;
-import com.vaadin.shared.ui.dnd.ButtonDragSourceState;
-import com.vaadin.ui.Button;
-
-/**
- * Extension to make Button a drag source for HTML5 drag and drop functionality.
- *
- * @author Vaadin Ltd.
- * @since 8.1
- */
-@Widgetset("com.vaadin.DefaultWidgetSet")
-public class ButtonDragSource extends DragSourceExtension<Button> {
-
-    public ButtonDragSource(Button target) {
-        super(target);
-    }
-
-    @Override
-    protected ButtonDragSourceState getState() {
-        return (ButtonDragSourceState) super.getState();
-    }
-
-    @Override
-    protected ButtonDragSourceState getState(boolean markAsDirty) {
-        return (ButtonDragSourceState) super.getState(markAsDirty);
-    }
-}
diff --git a/server/src/main/java/com/vaadin/server/DragAndDropService.java b/server/src/main/java/com/vaadin/server/DragAndDropService.java
index 11b830352f..64926c531c 100644
--- a/server/src/main/java/com/vaadin/server/DragAndDropService.java
+++ b/server/src/main/java/com/vaadin/server/DragAndDropService.java
@@ -33,14 +33,14 @@ import com.vaadin.event.dd.DropTarget;
 import com.vaadin.event.dd.TargetDetails;
 import com.vaadin.event.dd.TargetDetailsImpl;
 import com.vaadin.event.dd.acceptcriteria.AcceptCriterion;
-import com.vaadin.event.dnd.DragSourceExtension;
-import com.vaadin.event.dnd.DropTargetExtension;
 import com.vaadin.shared.ApplicationConstants;
 import com.vaadin.shared.Registration;
 import com.vaadin.shared.communication.SharedState;
 import com.vaadin.shared.ui.dd.DragEventType;
 import com.vaadin.ui.Component;
 import com.vaadin.ui.UI;
+import com.vaadin.ui.dnd.DragSourceExtension;
+import com.vaadin.ui.dnd.DropTargetExtension;
 
 import elemental.json.JsonObject;
 
diff --git a/server/src/main/java/com/vaadin/ui/DragAndDropWrapper.java b/server/src/main/java/com/vaadin/ui/DragAndDropWrapper.java
index 591cee6be5..194a354ad0 100644
--- a/server/src/main/java/com/vaadin/ui/DragAndDropWrapper.java
+++ b/server/src/main/java/com/vaadin/ui/DragAndDropWrapper.java
@@ -33,8 +33,6 @@ import com.vaadin.event.dd.DropHandler;
 import com.vaadin.event.dd.DropTarget;
 import com.vaadin.event.dd.TargetDetails;
 import com.vaadin.event.dd.TargetDetailsImpl;
-import com.vaadin.event.dnd.DragSourceExtension;
-import com.vaadin.event.dnd.DropTargetExtension;
 import com.vaadin.server.PaintException;
 import com.vaadin.server.PaintTarget;
 import com.vaadin.server.StreamVariable;
@@ -45,6 +43,8 @@ import com.vaadin.shared.ui.draganddropwrapper.DragAndDropWrapperConstants;
 import com.vaadin.shared.ui.draganddropwrapper.DragAndDropWrapperServerRpc;
 import com.vaadin.shared.ui.draganddropwrapper.DragAndDropWrapperState;
 import com.vaadin.ui.declarative.DesignContext;
+import com.vaadin.ui.dnd.DragSourceExtension;
+import com.vaadin.ui.dnd.DropTargetExtension;
 
 /**
  * @author Vaadin Ltd
diff --git a/server/src/main/java/com/vaadin/ui/Html5File.java b/server/src/main/java/com/vaadin/ui/Html5File.java
index b4434e75c9..4480e3d59b 100644
--- a/server/src/main/java/com/vaadin/ui/Html5File.java
+++ b/server/src/main/java/com/vaadin/ui/Html5File.java
@@ -32,7 +32,17 @@ public class Html5File implements Serializable {
     private StreamVariable streamVariable;
     private final String type;
 
-    Html5File(String name, long size, String mimeType) {
+    /**
+     * Constructs a new Html5 file wrapper.
+     *
+     * @param name
+     *            the file name
+     * @param size
+     *            the size of the file
+     * @param mimeType
+     *            the type of the file
+     */
+    public Html5File(String name, long size, String mimeType) {
         this.name = name;
         this.size = size;
         type = mimeType;
diff --git a/server/src/main/java/com/vaadin/ui/UI.java b/server/src/main/java/com/vaadin/ui/UI.java
index 1928aabe87..ed2d58df3c 100644
--- a/server/src/main/java/com/vaadin/ui/UI.java
+++ b/server/src/main/java/com/vaadin/ui/UI.java
@@ -44,8 +44,6 @@ import com.vaadin.event.MouseEvents.ClickListener;
 import com.vaadin.event.UIEvents.PollEvent;
 import com.vaadin.event.UIEvents.PollListener;
 import com.vaadin.event.UIEvents.PollNotifier;
-import com.vaadin.event.dnd.DragSourceExtension;
-import com.vaadin.event.dnd.DropTargetExtension;
 import com.vaadin.navigator.Navigator;
 import com.vaadin.server.ClientConnector;
 import com.vaadin.server.ComponentSizeValidator;
@@ -83,6 +81,8 @@ import com.vaadin.ui.Component.Focusable;
 import com.vaadin.ui.Dependency.Type;
 import com.vaadin.ui.Window.WindowOrderChangeListener;
 import com.vaadin.ui.declarative.Design;
+import com.vaadin.ui.dnd.DragSourceExtension;
+import com.vaadin.ui.dnd.DropTargetExtension;
 import com.vaadin.util.ConnectorHelper;
 import com.vaadin.util.CurrentInstance;
 import com.vaadin.util.ReflectTools;
diff --git a/server/src/main/java/com/vaadin/event/dnd/grid/GridDragEndEvent.java b/server/src/main/java/com/vaadin/ui/components/grid/GridDragEndEvent.java
index 06c583fc57..27fcf222fa 100644
--- a/server/src/main/java/com/vaadin/event/dnd/grid/GridDragEndEvent.java
+++ b/server/src/main/java/com/vaadin/ui/components/grid/GridDragEndEvent.java
@@ -13,14 +13,14 @@
  * License for the specific language governing permissions and limitations under
  * the License.
  */
-package com.vaadin.event.dnd.grid;
+package com.vaadin.ui.components.grid;
 
+import java.util.Collections;
 import java.util.Set;
 
-import com.vaadin.event.dnd.DragEndEvent;
 import com.vaadin.shared.ui.dnd.DropEffect;
 import com.vaadin.ui.Grid;
-import com.vaadin.ui.GridDragSource;
+import com.vaadin.ui.dnd.event.DragEndEvent;
 
 /**
  * Drop event on an HTML5 drop target {@link Grid} row.
@@ -55,9 +55,9 @@ public class GridDragEndEvent<T> extends DragEndEvent<Grid<T>> {
     /**
      * Get the dragged row items.
      *
-     * @return Set of row items that were being dragged.
+     * @return an unmodifiable set of items that were being dragged.
      */
     public Set<T> getDraggedItems() {
-        return draggedItems;
+        return Collections.unmodifiableSet(draggedItems);
     }
 }
diff --git a/server/src/main/java/com/vaadin/event/dnd/grid/GridDragEndListener.java b/server/src/main/java/com/vaadin/ui/components/grid/GridDragEndListener.java
index eb2b90fa64..d41a58bbb6 100644
--- a/server/src/main/java/com/vaadin/event/dnd/grid/GridDragEndListener.java
+++ b/server/src/main/java/com/vaadin/ui/components/grid/GridDragEndListener.java
@@ -13,12 +13,11 @@
  * License for the specific language governing permissions and limitations under
  * the License.
  */
-package com.vaadin.event.dnd.grid;
+package com.vaadin.ui.components.grid;
 
 import java.lang.reflect.Method;
 
 import com.vaadin.event.ConnectorEventListener;
-import com.vaadin.ui.GridDragSource;
 
 /**
  * Drop listener for HTML5 drop on a Grid row.
diff --git a/server/src/main/java/com/vaadin/ui/GridDragSource.java b/server/src/main/java/com/vaadin/ui/components/grid/GridDragSource.java
index a7798b581a..741ba043c6 100644
--- a/server/src/main/java/com/vaadin/ui/GridDragSource.java
+++ b/server/src/main/java/com/vaadin/ui/components/grid/GridDragSource.java
@@ -13,7 +13,7 @@
  * License for the specific language governing permissions and limitations under
  * the License.
  */
-package com.vaadin.ui;
+package com.vaadin.ui.components.grid;
 
 import java.util.List;
 import java.util.Optional;
@@ -21,17 +21,14 @@ import java.util.Set;
 import java.util.stream.Collectors;
 
 import com.vaadin.data.provider.DataGenerator;
-import com.vaadin.event.dnd.DragSourceExtension;
-import com.vaadin.event.dnd.grid.GridDragEndEvent;
-import com.vaadin.event.dnd.grid.GridDragEndListener;
-import com.vaadin.event.dnd.grid.GridDragStartEvent;
-import com.vaadin.event.dnd.grid.GridDragStartListener;
 import com.vaadin.server.SerializableFunction;
 import com.vaadin.shared.Registration;
 import com.vaadin.shared.ui.dnd.DragSourceState;
 import com.vaadin.shared.ui.dnd.DropEffect;
 import com.vaadin.shared.ui.grid.GridDragSourceRpc;
 import com.vaadin.shared.ui.grid.GridDragSourceState;
+import com.vaadin.ui.Grid;
+import com.vaadin.ui.dnd.DragSourceExtension;
 
 import elemental.json.JsonObject;
 
@@ -71,18 +68,18 @@ public class GridDragSource<T> extends DragSourceExtension<Grid<T>> {
         dragDataGenerator = this::generateDragData;
 
         // Add drag data generator to Grid
-        target.addDataGenerator(dragDataGenerator);
+        target.getDataCommunicator().addDataGenerator(dragDataGenerator);
     }
 
     @Override
-    protected void registerDragSourceRpc(Grid<T> target) {
+    protected void registerDragSourceRpc() {
         registerRpc(new GridDragSourceRpc() {
             @Override
             public void dragStart(List<String> draggedItemKeys) {
 
-                GridDragStartEvent<T> event = new GridDragStartEvent<>(target,
-                        getState(false).effectAllowed,
-                        getDraggedItems(target, draggedItemKeys));
+                GridDragStartEvent<T> event = new GridDragStartEvent<>(
+                        getParent(), getState(false).effectAllowed,
+                        getDraggedItems(getParent(), draggedItemKeys));
 
                 fireEvent(event);
             }
@@ -91,8 +88,9 @@ public class GridDragSource<T> extends DragSourceExtension<Grid<T>> {
             public void dragEnd(DropEffect dropEffect,
                     List<String> draggedItemKeys) {
 
-                GridDragEndEvent<T> event = new GridDragEndEvent<>(target,
-                        dropEffect, getDraggedItems(target, draggedItemKeys));
+                GridDragEndEvent<T> event = new GridDragEndEvent<>(getParent(),
+                        dropEffect,
+                        getDraggedItems(getParent(), draggedItemKeys));
 
                 fireEvent(event);
             }
@@ -135,7 +133,7 @@ public class GridDragSource<T> extends DragSourceExtension<Grid<T>> {
      * {@link JsonObject} to be appended to the row data.
      * <p>
      * Example:
-     * 
+     *
      * <pre>
      * dragSourceExtension.setDragDataGenerator(item -> {
      *     JsonObject dragData = Json.createObject();
@@ -211,7 +209,8 @@ public class GridDragSource<T> extends DragSourceExtension<Grid<T>> {
     public void remove() {
         super.remove();
 
-        getParent().removeDataGenerator(dragDataGenerator);
+        getParent().getDataCommunicator()
+                .removeDataGenerator(dragDataGenerator);
     }
 
     @Override
diff --git a/server/src/main/java/com/vaadin/event/dnd/grid/GridDragStartEvent.java b/server/src/main/java/com/vaadin/ui/components/grid/GridDragStartEvent.java
index 35691d20c2..576dca4ef5 100644
--- a/server/src/main/java/com/vaadin/event/dnd/grid/GridDragStartEvent.java
+++ b/server/src/main/java/com/vaadin/ui/components/grid/GridDragStartEvent.java
@@ -13,14 +13,14 @@
  * License for the specific language governing permissions and limitations under
  * the License.
  */
-package com.vaadin.event.dnd.grid;
+package com.vaadin.ui.components.grid;
 
+import java.util.Collections;
 import java.util.Set;
 
-import com.vaadin.event.dnd.DragStartEvent;
 import com.vaadin.shared.ui.dnd.EffectAllowed;
 import com.vaadin.ui.Grid;
-import com.vaadin.ui.GridDragSource;
+import com.vaadin.ui.dnd.event.DragStartEvent;
 
 /**
  * Drag start event on an HTML5 drag source {@link Grid} row.
@@ -55,9 +55,9 @@ public class GridDragStartEvent<T> extends DragStartEvent<Grid<T>> {
     /**
      * Get the dragged row items.
      *
-     * @return Set of row items that are being dragged.
+     * @return an unmodifiable set of items that are being dragged.
      */
     public Set<T> getDraggedItems() {
-        return draggedItems;
+        return Collections.unmodifiableSet(draggedItems);
     }
 }
diff --git a/server/src/main/java/com/vaadin/event/dnd/grid/GridDragStartListener.java b/server/src/main/java/com/vaadin/ui/components/grid/GridDragStartListener.java
index 0d1e071eea..10f57e85c1 100644
--- a/server/src/main/java/com/vaadin/event/dnd/grid/GridDragStartListener.java
+++ b/server/src/main/java/com/vaadin/ui/components/grid/GridDragStartListener.java
@@ -13,12 +13,11 @@
  * License for the specific language governing permissions and limitations under
  * the License.
  */
-package com.vaadin.event.dnd.grid;
+package com.vaadin.ui.components.grid;
 
 import java.lang.reflect.Method;
 
 import com.vaadin.event.ConnectorEventListener;
-import com.vaadin.ui.GridDragSource;
 
 /**
  * Drag start listener for HTML5 drag start on a Grid row.
diff --git a/server/src/main/java/com/vaadin/event/dnd/grid/GridDropEvent.java b/server/src/main/java/com/vaadin/ui/components/grid/GridDropEvent.java
index df634cf559..40df9f254f 100644
--- a/server/src/main/java/com/vaadin/event/dnd/grid/GridDropEvent.java
+++ b/server/src/main/java/com/vaadin/ui/components/grid/GridDropEvent.java
@@ -13,15 +13,14 @@
  * License for the specific language governing permissions and limitations under
  * the License.
  */
-package com.vaadin.event.dnd.grid;
+package com.vaadin.ui.components.grid;
 
-import com.vaadin.event.dnd.DragSourceExtension;
-import com.vaadin.event.dnd.DropEvent;
 import com.vaadin.shared.ui.dnd.DropEffect;
 import com.vaadin.shared.ui.grid.DropLocation;
 import com.vaadin.ui.AbstractComponent;
 import com.vaadin.ui.Grid;
-import com.vaadin.ui.GridDropTarget;
+import com.vaadin.ui.dnd.DragSourceExtension;
+import com.vaadin.ui.dnd.event.DropEvent;
 
 /**
  * Drop event on an HTML5 drop target {@link Grid} row.
diff --git a/server/src/main/java/com/vaadin/event/dnd/grid/GridDropListener.java b/server/src/main/java/com/vaadin/ui/components/grid/GridDropListener.java
index 0bd48db2ca..efac802ae7 100644
--- a/server/src/main/java/com/vaadin/event/dnd/grid/GridDropListener.java
+++ b/server/src/main/java/com/vaadin/ui/components/grid/GridDropListener.java
@@ -13,12 +13,11 @@
  * License for the specific language governing permissions and limitations under
  * the License.
  */
-package com.vaadin.event.dnd.grid;
+package com.vaadin.ui.components.grid;
 
 import java.lang.reflect.Method;
 
 import com.vaadin.event.ConnectorEventListener;
-import com.vaadin.ui.GridDropTarget;
 
 /**
  * Drop listener for HTML5 drop on a Grid row.
diff --git a/server/src/main/java/com/vaadin/ui/GridDropTarget.java b/server/src/main/java/com/vaadin/ui/components/grid/GridDropTarget.java
index 021051130c..435f40da6e 100644
--- a/server/src/main/java/com/vaadin/ui/GridDropTarget.java
+++ b/server/src/main/java/com/vaadin/ui/components/grid/GridDropTarget.java
@@ -13,16 +13,15 @@
  * License for the specific language governing permissions and limitations under
  * the License.
  */
-package com.vaadin.ui;
+package com.vaadin.ui.components.grid;
 
-import com.vaadin.event.dnd.DropTargetExtension;
-import com.vaadin.event.dnd.grid.GridDropEvent;
-import com.vaadin.event.dnd.grid.GridDropListener;
 import com.vaadin.shared.Registration;
 import com.vaadin.shared.ui.dnd.DropEffect;
 import com.vaadin.shared.ui.grid.DropMode;
 import com.vaadin.shared.ui.grid.GridDropTargetRpc;
 import com.vaadin.shared.ui.grid.GridDropTargetState;
+import com.vaadin.ui.Grid;
+import com.vaadin.ui.dnd.DropTargetExtension;
 
 /**
  * Makes the rows of a Grid HTML5 drop targets. This is the server side
@@ -130,14 +129,14 @@ public class GridDropTarget<T> extends DropTargetExtension<Grid<T>> {
     }
 
     @Override
-    protected void registerDropTargetRpc(Grid<T> target) {
+    protected void registerDropTargetRpc() {
         registerRpc((GridDropTargetRpc) (dataTransferText, dropEffect, rowKey,
                 dropLocation) -> {
 
-            T dropTargetRow = target.getDataCommunicator().getKeyMapper()
+            T dropTargetRow = getParent().getDataCommunicator().getKeyMapper()
                     .get(rowKey);
 
-            GridDropEvent<T> event = new GridDropEvent<>(target,
+            GridDropEvent<T> event = new GridDropEvent<>(getParent(),
                     dataTransferText,
                     DropEffect.valueOf(dropEffect.toUpperCase()),
                     getUI().getActiveDragSource(), dropTargetRow, dropLocation);
diff --git a/server/src/main/java/com/vaadin/event/dnd/DragSourceExtension.java b/server/src/main/java/com/vaadin/ui/dnd/DragSourceExtension.java
index 7ff84757d9..24192fa592 100644
--- a/server/src/main/java/com/vaadin/event/dnd/DragSourceExtension.java
+++ b/server/src/main/java/com/vaadin/ui/dnd/DragSourceExtension.java
@@ -13,7 +13,7 @@
  * License for the specific language governing permissions and limitations under
  * the License.
  */
-package com.vaadin.event.dnd;
+package com.vaadin.ui.dnd;
 
 import java.util.Objects;
 
@@ -25,18 +25,22 @@ import com.vaadin.shared.ui.dnd.DragSourceState;
 import com.vaadin.shared.ui.dnd.DropEffect;
 import com.vaadin.shared.ui.dnd.EffectAllowed;
 import com.vaadin.ui.AbstractComponent;
+import com.vaadin.ui.dnd.event.DragEndEvent;
+import com.vaadin.ui.dnd.event.DragEndListener;
+import com.vaadin.ui.dnd.event.DragStartEvent;
+import com.vaadin.ui.dnd.event.DragStartListener;
 
 /**
  * Extension to make a component drag source for HTML5 drag and drop
  * functionality.
  *
  * @param <T>
- *         Type of the component to be extended.
+ *            Type of the component to be extended.
  * @author Vaadin Ltd
  * @since 8.1
  */
-public class DragSourceExtension<T extends AbstractComponent> extends
-        AbstractExtension {
+public class DragSourceExtension<T extends AbstractComponent>
+        extends AbstractExtension {
 
     private Registration dragStartListenerHandle;
     private Registration dragEndListenerHandle;
@@ -51,22 +55,19 @@ public class DragSourceExtension<T extends AbstractComponent> extends
      * Extends {@code target} component and makes it a drag source.
      *
      * @param target
-     *         Component to be extended.
+     *            Component to be extended.
      */
     public DragSourceExtension(T target) {
-
-        registerDragSourceRpc(target);
-
         super.extend(target);
 
         initListeners();
     }
 
     /**
-     * Initializes the event listeners this drag source is using.
+     * Initializes dragstart and -end event listeners for this drag source to
+     * capture the active drag source for the UI.
      */
-    protected void initListeners() {
-
+    private void initListeners() {
         // Set current extension as active drag source in the UI
         dragStartListenerHandle = addDragStartListener(
                 event -> getUI().setActiveDragSource(this));
@@ -76,29 +77,58 @@ public class DragSourceExtension<T extends AbstractComponent> extends
                 event -> getUI().setActiveDragSource(null));
     }
 
+    @Override
+    public void attach() {
+        super.attach();
+
+        registerDragSourceRpc();
+    }
+
     /**
-     * Register server RPC.
-     *
-     * @param target
-     *         Extended component.
+     * Registers the server side RPC methods invoked from client side on
+     * <code>dragstart</code> and <code>dragend</code> events.
+     * <p>
+     * Override this method if you have custom RPC interface for transmitting
+     * those events with more data. If just need to do additional things before
+     * firing the events, then you should override {@link #onDragStart()} and
+     * {@link #onDragEnd(DropEffect)} instead.
      */
-    protected void registerDragSourceRpc(T target) {
+    protected void registerDragSourceRpc() {
         registerRpc(new DragSourceRpc() {
             @Override
             public void dragStart() {
-                DragStartEvent<T> event = new DragStartEvent<>(target,
-                        getState(false).effectAllowed);
-                fireEvent(event);
+                onDragStart();
             }
 
             @Override
             public void dragEnd(DropEffect dropEffect) {
-                DragEndEvent<T> event = new DragEndEvent<>(target, dropEffect);
-                fireEvent(event);
+                onDragEnd(dropEffect);
             }
         });
     }
 
+    /**
+     * Method invoked when a <code>dragstart</code> has been sent from client
+     * side. Fires the {@link DragStartEvent}.
+     */
+    protected void onDragStart() {
+        DragStartEvent<T> event = new DragStartEvent<>(getParent(),
+                getState(false).effectAllowed);
+        fireEvent(event);
+    }
+
+    /**
+     * Method invoked when a <code>dragend</code> has been sent from client
+     * side. Fires the {@link DragEndEvent}.
+     *
+     * @param dropEffect
+     *            the drop effect on the dragend
+     */
+    protected void onDragEnd(DropEffect dropEffect) {
+        DragEndEvent<T> event = new DragEndEvent<>(getParent(), dropEffect);
+        fireEvent(event);
+    }
+
     @Override
     public void remove() {
         super.remove();
@@ -117,7 +147,7 @@ public class DragSourceExtension<T extends AbstractComponent> extends
      * equivalent to {@link EffectAllowed#ALL}.
      *
      * @param effect
-     *         Effects to allow for this draggable element. Cannot be {@code
+     *            Effects to allow for this draggable element. Cannot be {@code
      *         null}.
      */
     public void setEffectAllowed(EffectAllowed effect) {
@@ -146,7 +176,7 @@ public class DragSourceExtension<T extends AbstractComponent> extends
      * data)} method.
      *
      * @param data
-     *         Data to be set for the client side draggable element.
+     *            Data to be set for the client side draggable element.
      */
     public void setDataTransferText(String data) {
         getState().dataTransferText = data;
@@ -163,19 +193,12 @@ public class DragSourceExtension<T extends AbstractComponent> extends
     }
 
     /**
-     * Clears data of type {@code "text"} in this drag source element.
-     */
-    public void clearDataTransferText() {
-        getState().dataTransferText = null;
-    }
-
-    /**
      * Set server side drag data. This data is available in the drop event and
      * can be used to transfer data between drag source and drop target if they
      * are in the same UI.
      *
      * @param data
-     *         Data to transfer to drop event.
+     *            Data to transfer to drop event.
      */
     public void setDragData(Object data) {
         dragData = data;
@@ -193,12 +216,12 @@ public class DragSourceExtension<T extends AbstractComponent> extends
     }
 
     /**
-     * Attaches dragstart listener for the current drag source. {@link
-     * DragStartListener#dragStart(DragStartEvent)} is called when dragstart
-     * event happens on the client side.
+     * Attaches dragstart listener for the current drag source.
+     * {@link DragStartListener#dragStart(DragStartEvent)} is called when
+     * dragstart event happens on the client side.
      *
      * @param listener
-     *         Listener to handle dragstart event.
+     *            Listener to handle dragstart event.
      * @return Handle to be used to remove this listener.
      */
     public Registration addDragStartListener(DragStartListener<T> listener) {
@@ -208,12 +231,12 @@ public class DragSourceExtension<T extends AbstractComponent> extends
     }
 
     /**
-     * Attaches dragend listener for the current drag source. {@link
-     * DragEndListener#dragEnd(DragEndEvent)} is called when dragend
+     * Attaches dragend listener for the current drag source.
+     * {@link DragEndListener#dragEnd(DragEndEvent)} is called when dragend
      * event happens on the client side.
      *
      * @param listener
-     *         Listener to handle dragend event.
+     *            Listener to handle dragend event.
      * @return Handle to be used to remove this listener.
      */
     public Registration addDragEndListener(DragEndListener<T> listener) {
@@ -225,7 +248,7 @@ public class DragSourceExtension<T extends AbstractComponent> extends
      * Set a custom drag image for the current drag source.
      *
      * @param imageResource
-     *         Resource of the image to be displayed as drag image.
+     *            Resource of the image to be displayed as drag image.
      */
     public void setDragImage(Resource imageResource) {
         setResource(DragSourceState.RESOURCE_DRAG_IMAGE, imageResource);
diff --git a/server/src/main/java/com/vaadin/event/dnd/DropTargetExtension.java b/server/src/main/java/com/vaadin/ui/dnd/DropTargetExtension.java
index 53266a2eea..24a0372f50 100644
--- a/server/src/main/java/com/vaadin/event/dnd/DropTargetExtension.java
+++ b/server/src/main/java/com/vaadin/ui/dnd/DropTargetExtension.java
@@ -13,7 +13,7 @@
  * License for the specific language governing permissions and limitations under
  * the License.
  */
-package com.vaadin.event.dnd;
+package com.vaadin.ui.dnd;
 
 import java.util.Objects;
 
@@ -23,10 +23,12 @@ import com.vaadin.shared.ui.dnd.DropEffect;
 import com.vaadin.shared.ui.dnd.DropTargetRpc;
 import com.vaadin.shared.ui.dnd.DropTargetState;
 import com.vaadin.ui.AbstractComponent;
+import com.vaadin.ui.dnd.event.DropEvent;
+import com.vaadin.ui.dnd.event.DropListener;
 
 /**
- * Extension to add drop target functionality to a widget for using HTML5 drag
- * and drop.
+ * Extension to make a component a drop target for HTML5 drag and drop
+ * functionality.
  *
  * @param <T>
  *            Type of the component to be extended.
@@ -43,29 +45,49 @@ public class DropTargetExtension<T extends AbstractComponent>
      *            Component to be extended.
      */
     public DropTargetExtension(T target) {
+        super.extend(target);
+    }
 
-        registerDropTargetRpc(target);
+    @Override
+    public void attach() {
+        super.attach();
 
-        super.extend(target);
+        registerDropTargetRpc();
     }
 
     /**
-     * Register server RPC.
-     *
-     * @param target
-     *            Extended component.
+     * Registers the server side RPC methods invoked from client side on
+     * <code>drop</code> event.
+     * <p>
+     * Override this method if you need to have a custom RPC interface for
+     * transmitting the drop event with more data. If just need to do additional
+     * things before firing the drop event, then you should override
+     * {@link #onDrop(String, DropEffect)} instead.
      */
-    protected void registerDropTargetRpc(T target) {
+    protected void registerDropTargetRpc() {
         registerRpc((DropTargetRpc) (dataTransferText, dropEffect) -> {
-            DropEvent<T> event = new DropEvent<>(target, dataTransferText,
-                    DropEffect.valueOf(dropEffect.toUpperCase()),
-                    getUI().getActiveDragSource());
-
-            fireEvent(event);
+            onDrop(dataTransferText,
+                    DropEffect.valueOf(dropEffect.toUpperCase()));
         });
     }
 
     /**
+     * Invoked when a <code>drop</code> has been received from client side.
+     * Fires the {@link DropEvent}.
+     *
+     * @param dataTransferText
+     *            the data transfer of type 'text' for the drop
+     * @param dropEffect
+     *            the drop effect
+     */
+    protected void onDrop(String dataTransferText, DropEffect dropEffect) {
+        DropEvent<T> event = new DropEvent<>(getParent(), dataTransferText,
+                dropEffect, getUI().getActiveDragSource());
+
+        fireEvent(event);
+    }
+
+    /**
      * Sets the drop effect for the current drop target. This is set to the
      * dropEffect on {@code dragenter} and {@code dragover} events.
      * <p>
@@ -104,9 +126,11 @@ public class DropTargetExtension<T extends AbstractComponent>
     }
 
     /**
-     * Sets criteria to allow drop on this drop target. The script executes when
-     * something is dragged on top of the target, and the drop is not allowed in
-     * case the script returns {@code false}.
+     * Sets a criteria script in JavaScript to allow drop on this drop target.
+     * The script is executed when something is dragged on top of the target,
+     * and the drop is not allowed in case the script returns {@code false}. If
+     * no script is set, then the drop is always accepted, if the set
+     * {@link #setDropEffect(DropEffect) dropEffect} matches the drag source.
      * <p>
      * <b>IMPORTANT:</b> Construct the criteria script carefully and do not
      * include untrusted sources such as user input. Always keep in mind that
diff --git a/server/src/main/java/com/vaadin/event/dnd/FileDropHandler.java b/server/src/main/java/com/vaadin/ui/dnd/FileDropHandler.java
index 5e74e44349..b9eb7d90eb 100644
--- a/server/src/main/java/com/vaadin/event/dnd/FileDropHandler.java
+++ b/server/src/main/java/com/vaadin/ui/dnd/FileDropHandler.java
@@ -13,11 +13,12 @@
  * License for the specific language governing permissions and limitations under
  * the License.
  */
-package com.vaadin.event.dnd;
+package com.vaadin.ui.dnd;
 
 import java.io.Serializable;
 
 import com.vaadin.ui.AbstractComponent;
+import com.vaadin.ui.dnd.event.FileDropEvent;
 
 /**
  * Handles the drop event on a file drop target.
@@ -26,7 +27,7 @@ import com.vaadin.ui.AbstractComponent;
  *         Type of the file drop target component.
  * @author Vaadin Ltd
  * @see FileDropEvent
- * @see com.vaadin.ui.FileDropTarget
+ * @see com.vaadin.ui.dnd.FileDropTarget
  * @since 8.1
  */
 public interface FileDropHandler<T extends AbstractComponent> extends
diff --git a/server/src/main/java/com/vaadin/ui/FileDropTarget.java b/server/src/main/java/com/vaadin/ui/dnd/FileDropTarget.java
index 88d2550691..bfb66c4fc4 100644
--- a/server/src/main/java/com/vaadin/ui/FileDropTarget.java
+++ b/server/src/main/java/com/vaadin/ui/dnd/FileDropTarget.java
@@ -13,15 +13,12 @@
  * License for the specific language governing permissions and limitations under
  * the License.
  */
-package com.vaadin.ui;
+package com.vaadin.ui.dnd;
 
 import java.io.OutputStream;
 import java.util.HashMap;
 import java.util.Map;
 
-import com.vaadin.event.dnd.DropTargetExtension;
-import com.vaadin.event.dnd.FileDropEvent;
-import com.vaadin.event.dnd.FileDropHandler;
 import com.vaadin.server.ServletPortletHelper;
 import com.vaadin.server.StreamVariable;
 import com.vaadin.shared.ApplicationConstants;
@@ -29,18 +26,28 @@ import com.vaadin.shared.ui.dnd.FileDropTargetClientRpc;
 import com.vaadin.shared.ui.dnd.FileDropTargetRpc;
 import com.vaadin.shared.ui.dnd.FileDropTargetState;
 import com.vaadin.shared.ui.dnd.FileParameters;
+import com.vaadin.ui.AbstractComponent;
+import com.vaadin.ui.ConnectorTracker;
+import com.vaadin.ui.Html5File;
+import com.vaadin.ui.UI;
+import com.vaadin.ui.dnd.event.FileDropEvent;
 
 /**
  * Extension to add drop target functionality to a widget for accepting and
  * uploading files.
+ * <p>
+ * Dropped files are handled in the {@link FileDropHandler} given in the
+ * constructor. The file details are first sent to the handler, which can then
+ * decide which files to upload to server by setting a {@link StreamVariable}
+ * with {@link Html5File#setStreamVariable(StreamVariable)}.
  *
  * @param <T>
- *         Type of the component to be extended.
+ *            Type of the component to be extended.
  * @author Vaadin Ltd
  * @since 8.1
  */
-public class FileDropTarget<T extends AbstractComponent> extends
-        DropTargetExtension<T> {
+public class FileDropTarget<T extends AbstractComponent>
+        extends DropTargetExtension<T> {
 
     /**
      * Handles the file drop event.
@@ -52,45 +59,57 @@ public class FileDropTarget<T extends AbstractComponent> extends
      * drop handler needs to be added to handle the file drop event.
      *
      * @param target
-     *         Component to be extended.
+     *            Component to be extended.
      * @param fileDropHandler
-     *         File drop handler that handles the file drop event.
+     *            File drop handler that handles the file drop event.
      * @see FileDropEvent
      */
     public FileDropTarget(T target, FileDropHandler<T> fileDropHandler) {
         super(target);
 
         this.fileDropHandler = fileDropHandler;
-    }
-
-    @Override
-    protected void registerDropTargetRpc(T target) {
-        super.registerDropTargetRpc(target);
 
         registerRpc(new FileDropTargetRpc() {
             @Override
             public void drop(Map<String, FileParameters> fileParams) {
-                Map<String, Html5File> files = new HashMap<>();
-                Map<String, String> urls = new HashMap<>();
-
-                // Create a collection of html5 files
-                fileParams.forEach((id, fileParameters) -> {
-                    Html5File html5File = new Html5File(
-                            fileParameters.getName(), fileParameters.getSize(),
-                            fileParameters.getMime());
-                    files.put(id, html5File);
-                });
+                onDrop(fileParams);
+            }
 
-                // Call drop handler with the collection of dropped files
-                FileDropEvent<T> event = new FileDropEvent<>(target,
-                        files.values());
-                fileDropHandler.drop(event);
+            @Override
+            public void poll() {
+                // Polling server for changes after upload finished
+            }
+        });
+    }
 
-                // Create upload URLs for the files that the drop handler
-                // attached stream variable to
-                files.entrySet().stream()
-                        .filter(entry -> entry.getValue().getStreamVariable()
-                                != null).forEach(entry -> {
+    /**
+     * Invoked when a file or files have been dropped on client side. Fires the
+     * {@link FileDropEvent}.
+     *
+     * @param fileParams
+     *            map from file ids to actual file details
+     */
+    protected void onDrop(Map<String, FileParameters> fileParams) {
+        Map<String, Html5File> files = new HashMap<>();
+        Map<String, String> urls = new HashMap<>();
+
+        // Create a collection of html5 files
+        fileParams.forEach((id, fileParameters) -> {
+            Html5File html5File = new Html5File(fileParameters.getName(),
+                    fileParameters.getSize(), fileParameters.getMime());
+            files.put(id, html5File);
+        });
+
+        // Call drop handler with the collection of dropped files
+        FileDropEvent<T> event = new FileDropEvent<>(getParent(),
+                files.values());
+        fileDropHandler.drop(event);
+
+        // Create upload URLs for the files that the drop handler
+        // attached stream variable to
+        files.entrySet().stream()
+                .filter(entry -> entry.getValue().getStreamVariable() != null)
+                .forEach(entry -> {
                     String id = entry.getKey();
                     Html5File file = entry.getValue();
 
@@ -98,28 +117,20 @@ public class FileDropTarget<T extends AbstractComponent> extends
                     urls.put(id, url);
                 });
 
-                // Send upload URLs to the client if there are files to be
-                // uploaded
-                if (urls.size() > 0) {
-                    getRpcProxy(FileDropTargetClientRpc.class)
-                            .sendUploadUrl(urls);
-                }
-            }
-
-            @Override
-            public void poll() {
-                // Polling server for changes after upload finished
-            }
-        });
+        // Send upload URLs to the client if there are files to be
+        // uploaded
+        if (urls.size() > 0) {
+            getRpcProxy(FileDropTargetClientRpc.class).sendUploadUrl(urls);
+        }
     }
 
     /**
      * Creates an upload URL for the given file and file ID.
      *
      * @param file
-     *         File to be uploaded.
+     *            File to be uploaded.
      * @param id
-     *         Generated ID for the file.
+     *            Generated ID for the file.
      * @return Upload URL for uploading the file to the server.
      */
     private String createUrl(Html5File file, String id) {
@@ -147,7 +158,6 @@ public class FileDropTarget<T extends AbstractComponent> extends
         return (FileDropTargetState) super.getState();
     }
 
-
     @Override
     protected FileDropTargetState getState(boolean markAsDirty) {
         return (FileDropTargetState) super.getState(markAsDirty);
@@ -161,7 +171,7 @@ public class FileDropTarget<T extends AbstractComponent> extends
     @Override
     @SuppressWarnings("unchecked")
     public T getParent() {
-        return (T) super.getParent();
+        return super.getParent();
     }
 
     private class FileReceiver implements StreamVariable {
diff --git a/server/src/main/java/com/vaadin/event/dnd/DragEndEvent.java b/server/src/main/java/com/vaadin/ui/dnd/event/DragEndEvent.java
index 5e0739d2d9..592a81497f 100644
--- a/server/src/main/java/com/vaadin/event/dnd/DragEndEvent.java
+++ b/server/src/main/java/com/vaadin/ui/dnd/event/DragEndEvent.java
@@ -13,12 +13,14 @@
  * License for the specific language governing permissions and limitations under
  * the License.
  */
-package com.vaadin.event.dnd;
+package com.vaadin.ui.dnd.event;
 
 import com.vaadin.shared.ui.dnd.DropEffect;
 import com.vaadin.shared.ui.dnd.EffectAllowed;
 import com.vaadin.ui.AbstractComponent;
 import com.vaadin.ui.Component;
+import com.vaadin.ui.dnd.DragSourceExtension;
+import com.vaadin.ui.dnd.DropTargetExtension;
 
 /**
  * HTML5 drag end event.
diff --git a/server/src/main/java/com/vaadin/event/dnd/DragEndListener.java b/server/src/main/java/com/vaadin/ui/dnd/event/DragEndListener.java
index 55b55b2bcd..b8ab67279e 100644
--- a/server/src/main/java/com/vaadin/event/dnd/DragEndListener.java
+++ b/server/src/main/java/com/vaadin/ui/dnd/event/DragEndListener.java
@@ -13,12 +13,13 @@
  * License for the specific language governing permissions and limitations under
  * the License.
  */
-package com.vaadin.event.dnd;
+package com.vaadin.ui.dnd.event;
 
 import java.lang.reflect.Method;
 
 import com.vaadin.event.ConnectorEventListener;
 import com.vaadin.ui.AbstractComponent;
+import com.vaadin.ui.dnd.DragSourceExtension;
 
 /**
  * Interface to be implemented when creating a dragend listener on a drag
diff --git a/server/src/main/java/com/vaadin/event/dnd/DragStartEvent.java b/server/src/main/java/com/vaadin/ui/dnd/event/DragStartEvent.java
index 2022f42a00..14d04bad96 100644
--- a/server/src/main/java/com/vaadin/event/dnd/DragStartEvent.java
+++ b/server/src/main/java/com/vaadin/ui/dnd/event/DragStartEvent.java
@@ -13,11 +13,12 @@
  * License for the specific language governing permissions and limitations under
  * the License.
  */
-package com.vaadin.event.dnd;
+package com.vaadin.ui.dnd.event;
 
 import com.vaadin.shared.ui.dnd.EffectAllowed;
 import com.vaadin.ui.AbstractComponent;
 import com.vaadin.ui.Component;
+import com.vaadin.ui.dnd.DragSourceExtension;
 
 /**
  * HTML5 drag start event.
diff --git a/server/src/main/java/com/vaadin/event/dnd/DragStartListener.java b/server/src/main/java/com/vaadin/ui/dnd/event/DragStartListener.java
index 530a0f113b..42c702f7db 100644
--- a/server/src/main/java/com/vaadin/event/dnd/DragStartListener.java
+++ b/server/src/main/java/com/vaadin/ui/dnd/event/DragStartListener.java
@@ -13,12 +13,13 @@
  * License for the specific language governing permissions and limitations under
  * the License.
  */
-package com.vaadin.event.dnd;
+package com.vaadin.ui.dnd.event;
 
 import java.lang.reflect.Method;
 
 import com.vaadin.event.ConnectorEventListener;
 import com.vaadin.ui.AbstractComponent;
+import com.vaadin.ui.dnd.DragSourceExtension;
 
 /**
  * Interface to be implemented when creating a dragstart listener on a drag
diff --git a/server/src/main/java/com/vaadin/event/dnd/DropEvent.java b/server/src/main/java/com/vaadin/ui/dnd/event/DropEvent.java
index caa80a88ae..45dabd0a62 100644
--- a/server/src/main/java/com/vaadin/event/dnd/DropEvent.java
+++ b/server/src/main/java/com/vaadin/ui/dnd/event/DropEvent.java
@@ -13,13 +13,15 @@
  * License for the specific language governing permissions and limitations under
  * the License.
  */
-package com.vaadin.event.dnd;
+package com.vaadin.ui.dnd.event;
 
 import java.util.Optional;
 
 import com.vaadin.shared.ui.dnd.DropEffect;
 import com.vaadin.ui.AbstractComponent;
 import com.vaadin.ui.Component;
+import com.vaadin.ui.dnd.DragSourceExtension;
+import com.vaadin.ui.dnd.DropTargetExtension;
 
 /**
  * Server side drop event. Fired when an HTML5 drop happens.
diff --git a/server/src/main/java/com/vaadin/event/dnd/DropListener.java b/server/src/main/java/com/vaadin/ui/dnd/event/DropListener.java
index c10f51569c..5f31676468 100644
--- a/server/src/main/java/com/vaadin/event/dnd/DropListener.java
+++ b/server/src/main/java/com/vaadin/ui/dnd/event/DropListener.java
@@ -13,12 +13,13 @@
  * License for the specific language governing permissions and limitations under
  * the License.
  */
-package com.vaadin.event.dnd;
+package com.vaadin.ui.dnd.event;
 
 import java.lang.reflect.Method;
 
 import com.vaadin.event.ConnectorEventListener;
 import com.vaadin.ui.AbstractComponent;
+import com.vaadin.ui.dnd.DropTargetExtension;
 
 /**
  * Interface to be implemented when creating a drop listener on a drop target
diff --git a/server/src/main/java/com/vaadin/event/dnd/FileDropEvent.java b/server/src/main/java/com/vaadin/ui/dnd/event/FileDropEvent.java
index 7ad5f410bf..331b83c784 100644
--- a/server/src/main/java/com/vaadin/event/dnd/FileDropEvent.java
+++ b/server/src/main/java/com/vaadin/ui/dnd/event/FileDropEvent.java
@@ -13,7 +13,7 @@
  * License for the specific language governing permissions and limitations under
  * the License.
  */
-package com.vaadin.event.dnd;
+package com.vaadin.ui.dnd.event;
 
 import java.util.Collection;
 import java.util.List;
@@ -21,6 +21,7 @@ import java.util.List;
 import com.vaadin.ui.AbstractComponent;
 import com.vaadin.ui.Component;
 import com.vaadin.ui.Html5File;
+import com.vaadin.ui.dnd.FileDropHandler;
 
 /**
  * File drop event that contains the collection of files dropped on a file drop