Make DragSource extension/component available in DropEvent (#8636)

* Make DragSource extension/component available in DropEvent (resolves #8439)

* Update drag and drop test to use new API

* Change type of drag source and update javadoc

* Use existing data map instead of DataTransfer

11 files changed, 87 insertions, 55 deletions

diff --git a/client/src/main/java/com/vaadin/client/extensions/DragSourceExtensionConnector.java b/client/src/main/java/com/vaadin/client/extensions/DragSourceExtensionConnector.java
index 532b9877fc..b823167572 100644
--- a/client/src/main/java/com/vaadin/client/extensions/DragSourceExtensionConnector.java
+++ b/client/src/main/java/com/vaadin/client/extensions/DragSourceExtensionConnector.java
@@ -42,6 +42,11 @@ public class DragSourceExtensionConnector extends AbstractExtensionConnector {
 
     private static final String CLASS_DRAGGABLE = "v-draggable";
 
+    /**
+     * Data type for storing drag source extension connector's ID
+     */
+    static final String DATA_TYPE_DRAG_SOURCE_ID = "drag-source-id";
+
     // Create event listeners
     private final EventListener dragStartListener = this::onDragStart;
     private final EventListener dragEndListener = this::onDragEnd;
@@ -104,6 +109,10 @@ public class DragSourceExtensionConnector extends AbstractExtensionConnector {
             nativeEvent.getDataTransfer().setData(format, data.get(format));
         }
 
+        // Store the extension's connector ID in DataTransfer.data
+        nativeEvent.getDataTransfer()
+                .setData(DATA_TYPE_DRAG_SOURCE_ID, getConnectorId());
+
         // Initiate firing server side dragstart event when there is a
         // DragStartListener attached on the server side
         if (hasEventListener(DragSourceState.EVENT_DRAGSTART)) {
diff --git a/client/src/main/java/com/vaadin/client/extensions/DropTargetExtensionConnector.java b/client/src/main/java/com/vaadin/client/extensions/DropTargetExtensionConnector.java
index 3a9cbbfe84..37d62ad7c0 100644
--- a/client/src/main/java/com/vaadin/client/extensions/DropTargetExtensionConnector.java
+++ b/client/src/main/java/com/vaadin/client/extensions/DropTargetExtensionConnector.java
@@ -193,7 +193,8 @@ public class DropTargetExtensionConnector extends AbstractExtensionConnector {
             }
 
             getRpcProxy(DropTargetRpc.class)
-                    .drop(types, data, getState().dropEffect);
+                    .drop(types, data, getState().dropEffect, data.get(
+                            DragSourceExtensionConnector.DATA_TYPE_DRAG_SOURCE_ID));
         }
 
         removeTargetIndicator(getDropTargetElement());
diff --git a/server/src/main/java/com/vaadin/event/dnd/DragEndEvent.java b/server/src/main/java/com/vaadin/event/dnd/DragEndEvent.java
index 47abea4eae..9de3611457 100644
--- a/server/src/main/java/com/vaadin/event/dnd/DragEndEvent.java
+++ b/server/src/main/java/com/vaadin/event/dnd/DragEndEvent.java
@@ -20,6 +20,7 @@ import java.util.List;
 import java.util.Map;
 
 import com.vaadin.shared.ui.dnd.EffectAllowed;
+import com.vaadin.ui.AbstractComponent;
 import com.vaadin.ui.Component;
 
 /**
@@ -29,7 +30,7 @@ import com.vaadin.ui.Component;
  *         Type of the component that was dragged.
  * @see DragSourceExtension#addDragEndListener(DragEndListener)
  */
-public class DragEndEvent<T extends Component> extends Component.Event {
+public class DragEndEvent<T extends AbstractComponent> extends Component.Event {
     private final Map<String, String> data;
     private final EffectAllowed effectAllowed;
 
diff --git a/server/src/main/java/com/vaadin/event/dnd/DragEndListener.java b/server/src/main/java/com/vaadin/event/dnd/DragEndListener.java
index 7b35bcab1d..51e113e4fd 100644
--- a/server/src/main/java/com/vaadin/event/dnd/DragEndListener.java
+++ b/server/src/main/java/com/vaadin/event/dnd/DragEndListener.java
@@ -18,7 +18,7 @@ package com.vaadin.event.dnd;
 import java.lang.reflect.Method;
 
 import com.vaadin.event.ConnectorEventListener;
-import com.vaadin.ui.Component;
+import com.vaadin.ui.AbstractComponent;
 
 /**
  * Interface to be implemented when creating a dragend listener on a drag
@@ -29,7 +29,7 @@ import com.vaadin.ui.Component;
  * @see DragSourceExtension#addDragEndListener(DragEndListener)
  */
 @FunctionalInterface
-public interface DragEndListener<T extends Component> extends
+public interface DragEndListener<T extends AbstractComponent> extends
         ConnectorEventListener {
     static final Method DRAGEND_METHOD = DragEndListener.class
             .getDeclaredMethods()[0];
diff --git a/server/src/main/java/com/vaadin/event/dnd/DragStartEvent.java b/server/src/main/java/com/vaadin/event/dnd/DragStartEvent.java
index de6a1a79f4..8e9f82551c 100644
--- a/server/src/main/java/com/vaadin/event/dnd/DragStartEvent.java
+++ b/server/src/main/java/com/vaadin/event/dnd/DragStartEvent.java
@@ -20,6 +20,7 @@ import java.util.List;
 import java.util.Map;
 
 import com.vaadin.shared.ui.dnd.EffectAllowed;
+import com.vaadin.ui.AbstractComponent;
 import com.vaadin.ui.Component;
 
 /**
@@ -30,7 +31,7 @@ import com.vaadin.ui.Component;
  *         Type of the component that is dragged.
  * @see DragSourceExtension#addDragStartListener(DragStartListener)
  */
-public class DragStartEvent<T extends Component> extends Component.Event {
+public class DragStartEvent<T extends AbstractComponent> extends Component.Event {
     private final Map<String, String> data;
     private final EffectAllowed effectAllowed;
 
diff --git a/server/src/main/java/com/vaadin/event/dnd/DragStartListener.java b/server/src/main/java/com/vaadin/event/dnd/DragStartListener.java
index a9536144d9..d56254c58d 100644
--- a/server/src/main/java/com/vaadin/event/dnd/DragStartListener.java
+++ b/server/src/main/java/com/vaadin/event/dnd/DragStartListener.java
@@ -18,7 +18,7 @@ package com.vaadin.event.dnd;
 import java.lang.reflect.Method;
 
 import com.vaadin.event.ConnectorEventListener;
-import com.vaadin.ui.Component;
+import com.vaadin.ui.AbstractComponent;
 
 /**
  * Interface to be implemented when creating a dragstart listener on a drag
@@ -29,7 +29,7 @@ import com.vaadin.ui.Component;
  * @see DragSourceExtension#addDragStartListener(DragStartListener)
  */
 @FunctionalInterface
-public interface DragStartListener<T extends Component> extends
+public interface DragStartListener<T extends AbstractComponent> extends
         ConnectorEventListener {
     static final Method DRAGSTART_METHOD = DragStartListener.class
             .getDeclaredMethods()[0];
diff --git a/server/src/main/java/com/vaadin/event/dnd/DropEvent.java b/server/src/main/java/com/vaadin/event/dnd/DropEvent.java
index 5257a06367..9a16efc097 100644
--- a/server/src/main/java/com/vaadin/event/dnd/DropEvent.java
+++ b/server/src/main/java/com/vaadin/event/dnd/DropEvent.java
@@ -18,8 +18,10 @@ package com.vaadin.event.dnd;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Optional;
 
 import com.vaadin.shared.ui.dnd.DropEffect;
+import com.vaadin.ui.AbstractComponent;
 import com.vaadin.ui.Component;
 
 /**
@@ -29,15 +31,17 @@ import com.vaadin.ui.Component;
  *         Type of the drop target component.
  * @see DropTargetExtension#addDropListener(DropListener)
  */
-public class DropEvent<T extends Component> extends Component.Event {
+public class DropEvent<T extends AbstractComponent> extends Component.Event {
     private final Map<String, String> data;
     private final DropEffect dropEffect;
+    private final DragSourceExtension<AbstractComponent> dragSourceExtension;
+    private final AbstractComponent dragSource;
 
     /**
      * Creates a server side drop event.
      *
-     * @param source
-     *         Component that is dragged.
+     * @param target
+     *         Component that received the drop.
      * @param types
      *         List of data types from {@code DataTransfer.types} object.
      * @param data
@@ -45,16 +49,24 @@ public class DropEvent<T extends Component> extends Component.Event {
      *         DataTransfer} object.
      * @param dropEffect
      *         Drop effect from {@code DataTransfer.dropEffect} object.
+     * @param dragSourceExtension
+     *         Drag source extension of the component that initiated the drop
+     *         event.
      */
-    public DropEvent(T source, List<String> types, Map<String, String> data,
-            DropEffect dropEffect) {
-        super(source);
+    public DropEvent(T target, List<String> types, Map<String, String> data,
+            DropEffect dropEffect,
+            DragSourceExtension<AbstractComponent> dragSourceExtension) {
+        super(target);
 
         // Create a linked map that preserves the order of types
         this.data = new LinkedHashMap<>();
         types.forEach(type -> this.data.put(type, data.get(type)));
 
         this.dropEffect = dropEffect;
+
+        this.dragSourceExtension = dragSourceExtension;
+        this.dragSource = Optional.ofNullable(dragSourceExtension)
+                .map(DragSourceExtension::getParent).orElse(null);
     }
 
     /**
@@ -79,6 +91,28 @@ public class DropEvent<T extends Component> extends Component.Event {
     }
 
     /**
+     * Returns the drag source component if the drag originated from a
+     * component in the same UI as the drop target component, or an empty
+     * optional.
+     *
+     * @return Drag source component or an empty optional.
+     */
+    public Optional<AbstractComponent> getDragSourceComponent() {
+        return Optional.ofNullable(dragSource);
+    }
+
+    /**
+     * Returns the extension of the drag source component if the drag
+     * originated from a component in the same UI as the drop target component,
+     * or an empty optional.
+     *
+     * @return Drag source extension or an empty optional
+     */
+    public Optional<DragSourceExtension<AbstractComponent>> getDragSourceExtension() {
+        return Optional.ofNullable(dragSourceExtension);
+    }
+
+    /**
      * Returns the drop target component where the drop event occurred.
      *
      * @return Component on which a drag source was dropped.
diff --git a/server/src/main/java/com/vaadin/event/dnd/DropListener.java b/server/src/main/java/com/vaadin/event/dnd/DropListener.java
index 41c1bfc6ff..98e8147fc3 100644
--- a/server/src/main/java/com/vaadin/event/dnd/DropListener.java
+++ b/server/src/main/java/com/vaadin/event/dnd/DropListener.java
@@ -18,7 +18,7 @@ package com.vaadin.event.dnd;
 import java.lang.reflect.Method;
 
 import com.vaadin.event.ConnectorEventListener;
-import com.vaadin.ui.Component;
+import com.vaadin.ui.AbstractComponent;
 
 /**
  * Interface to be implemented when creating a drop listener on a drop target
@@ -29,7 +29,7 @@ import com.vaadin.ui.Component;
  * @see DropTargetExtension#addDropListener(DropListener)
  */
 @FunctionalInterface
-public interface DropListener<T extends Component> extends
+public interface DropListener<T extends AbstractComponent> extends
         ConnectorEventListener {
     static final Method DROP_METHOD = DropListener.class
             .getDeclaredMethods()[0];
diff --git a/server/src/main/java/com/vaadin/event/dnd/DropTargetExtension.java b/server/src/main/java/com/vaadin/event/dnd/DropTargetExtension.java
index e6f1fe1214..887361e883 100644
--- a/server/src/main/java/com/vaadin/event/dnd/DropTargetExtension.java
+++ b/server/src/main/java/com/vaadin/event/dnd/DropTargetExtension.java
@@ -18,6 +18,7 @@ package com.vaadin.event.dnd;
 import java.util.Objects;
 
 import com.vaadin.server.AbstractExtension;
+import com.vaadin.server.ClientConnector;
 import com.vaadin.shared.Registration;
 import com.vaadin.shared.ui.dnd.DropEffect;
 import com.vaadin.shared.ui.dnd.DropTargetRpc;
@@ -41,9 +42,17 @@ public class DropTargetExtension<T extends AbstractComponent> extends
      *         Component to be extended.
      */
     public DropTargetExtension(T target) {
-        registerRpc((DropTargetRpc) (types, data, dropEffect) -> {
+        registerRpc((DropTargetRpc) (types, data, dropEffect, dataSourceId) -> {
+            DragSourceExtension dragSource = null;
+
+            ClientConnector connector = getUI().getConnectorTracker()
+                    .getConnector(dataSourceId);
+            if (connector != null && connector instanceof DragSourceExtension) {
+                dragSource = (DragSourceExtension) connector;
+            }
+
             DropEvent<T> event = new DropEvent<>(target, types, data,
-                    dropEffect);
+                    dropEffect, dragSource);
 
             fireEvent(event);
         });
diff --git a/shared/src/main/java/com/vaadin/shared/ui/dnd/DropTargetRpc.java b/shared/src/main/java/com/vaadin/shared/ui/dnd/DropTargetRpc.java
index dd21278277..9f335f010d 100644
--- a/shared/src/main/java/com/vaadin/shared/ui/dnd/DropTargetRpc.java
+++ b/shared/src/main/java/com/vaadin/shared/ui/dnd/DropTargetRpc.java
@@ -36,7 +36,9 @@ public interface DropTargetRpc extends ServerRpc {
      *         Contains data from {@code DataTransfer} object.
      * @param dropEffect
      *         Drop effect set for the drop target where drop happened.
+     * @param dragSourceId
+     *         Drag source component connector's ID.
      */
     public void drop(List<String> types, Map<String, String> data,
-            DropEffect dropEffect);
+            DropEffect dropEffect, String dragSourceId);
 }
diff --git a/uitest/src/main/java/com/vaadin/tests/dnd/DragAndDropCardShuffle.java b/uitest/src/main/java/com/vaadin/tests/dnd/DragAndDropCardShuffle.java
index 8f5df032cc..745297cde8 100644
--- a/uitest/src/main/java/com/vaadin/tests/dnd/DragAndDropCardShuffle.java
+++ b/uitest/src/main/java/com/vaadin/tests/dnd/DragAndDropCardShuffle.java
@@ -15,23 +15,17 @@
  */
 package com.vaadin.tests.dnd;
 
-import java.util.Optional;
-
 import com.vaadin.event.dnd.DragSourceExtension;
 import com.vaadin.event.dnd.DropTargetExtension;
-import com.vaadin.server.Extension;
 import com.vaadin.server.Page;
 import com.vaadin.server.VaadinRequest;
+import com.vaadin.shared.ui.dnd.DropEffect;
 import com.vaadin.tests.components.AbstractTestUIWithLog;
-import com.vaadin.ui.Component;
 import com.vaadin.ui.HorizontalLayout;
 import com.vaadin.ui.Label;
 
 public class DragAndDropCardShuffle extends AbstractTestUIWithLog {
 
-    // Data type for storing card position
-    private static final String DATA_INDEX = "index";
-
     // Create cards
     private final Label ace = new Label("A");
     private final Label jack = new Label("J");
@@ -74,10 +68,6 @@ public class DragAndDropCardShuffle extends AbstractTestUIWithLog {
         DragSourceExtension<Label> dragSource = new DragSourceExtension<>(
                 source);
 
-        // Set component position as transfer data
-        dragSource.setTransferData(DATA_INDEX,
-                String.valueOf(desk.getComponentIndex(source)));
-
         // Add listeners
         dragSource.addDragStartListener(event -> {
             event.getComponent().addStyleName("dragged");
@@ -95,36 +85,21 @@ public class DragAndDropCardShuffle extends AbstractTestUIWithLog {
         DropTargetExtension<Label> dropTarget = new DropTargetExtension<>(
                 target);
 
+        dropTarget.setDropEffect(DropEffect.MOVE);
+
         // Add listener
         dropTarget.addDropListener(event -> {
-            // Retrieve the source's position
-            int sourceIndex = Integer
-                    .valueOf(event.getTransferData(DATA_INDEX));
-
-            // Find source component
-            Component source = desk.getComponent(sourceIndex);
-
-            // Swap source and target components
-            desk.replaceComponent(target, source);
-
-            // Get DragSource extension for target component and set position data
-            Optional<Extension> targetExt = target.getExtensions().stream()
-                    .filter(e -> e instanceof DragSourceExtension).findFirst();
-            targetExt.ifPresent(extension -> {
-                ((DragSourceExtension) extension).setTransferData(DATA_INDEX,
-                        String.valueOf(desk.getComponentIndex(target)));
-            });
+            event.getDragSourceExtension().ifPresent(dragSource -> {
+                if (dragSource.getParent() instanceof Label) {
+                    Label source = (Label) dragSource.getParent();
 
-            // Get DragSource extension for source component and set position data
-            Optional<Extension> sourceExt = source.getExtensions().stream()
-                    .filter(e -> e instanceof DragSourceExtension).findFirst();
-            sourceExt.ifPresent(extension -> {
-                ((DragSourceExtension) extension).setTransferData(DATA_INDEX,
-                        String.valueOf(desk.getComponentIndex(source)));
-            });
+                    // Swap source and target components
+                    desk.replaceComponent(target, source);
 
-            log(((Label) source).getValue() + " dropped onto " + (event
-                    .getComponent()).getValue());
+                    log(source.getValue() + " dropped onto " + event
+                            .getComponent().getValue());
+                }
+            });
         });
     }