Remove support for transfer data type (#8910)

* Remove API for setting arbitrary drag data
* Store the drag source component in the UI

Fixes #8893 

6 files changed, 109 insertions, 154 deletions

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 d8244d1f16..f1176e1880 100644
--- a/server/src/main/java/com/vaadin/event/dnd/DragEndEvent.java
+++ b/server/src/main/java/com/vaadin/event/dnd/DragEndEvent.java
@@ -15,10 +15,6 @@
  */
 package com.vaadin.event.dnd;
 
-import java.util.LinkedHashMap;
-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;
@@ -33,7 +29,7 @@ import com.vaadin.ui.Component;
  * @since 8.1
  */
 public class DragEndEvent<T extends AbstractComponent> extends Component.Event {
-    private final Map<String, String> data;
+    private final String dataTransferText;
     private final EffectAllowed effectAllowed;
 
     /**
@@ -41,35 +37,30 @@ public class DragEndEvent<T extends AbstractComponent> extends Component.Event {
      *
      * @param source
      *         Component that was dragged.
-     * @param types
-     *         List of data types from {@code DataTransfer.types} object.
-     * @param data
-     *         Map containing all types and corresponding data from the {@code
-     *         DataTransfer} object.
+     * @param dataTransferText
+     *         Data of type {@code "text"} from the {@code DataTransfer}
+     *         object.
      * @param effectAllowed
      *         Allowed effects from {@code DataTransfer.effectAllowed} object.
      */
-    public DragEndEvent(T source, List<String> types, Map<String, String> data,
+    public DragEndEvent(T source, String dataTransferText,
             EffectAllowed effectAllowed) {
         super(source);
 
-        // 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.dataTransferText = dataTransferText;
 
         this.effectAllowed = effectAllowed;
     }
 
     /**
-     * Get data from the client side {@code DataTransfer} object.
+     * Get data of type {@code "text"} from the client side {@code DataTransfer}
+     * object.
      *
-     * @param format
-     *         Data format, e.g. {@code text/plain} or {@code text/uri-list}.
-     * @return Data for the given format if exists in the client side {@code
-     * DataTransfer}, otherwise {@code null}.
+     * @return Data of type {@code "text"} if exists in the client side {@code
+     * DataTransfer} object, otherwise {@literal null}.
      */
-    public String getTransferData(String format) {
-        return data != null ? data.get(format) : null;
+    public String getDataTransferText() {
+        return dataTransferText;
     }
 
     /**
diff --git a/server/src/main/java/com/vaadin/event/dnd/DragSourceExtension.java b/server/src/main/java/com/vaadin/event/dnd/DragSourceExtension.java
index 2e3d7e1c82..f7089c9b9e 100644
--- a/server/src/main/java/com/vaadin/event/dnd/DragSourceExtension.java
+++ b/server/src/main/java/com/vaadin/event/dnd/DragSourceExtension.java
@@ -15,9 +15,6 @@
  */
 package com.vaadin.event.dnd;
 
-import java.util.Collections;
-import java.util.LinkedHashMap;
-import java.util.Map;
 import java.util.Objects;
 
 import com.vaadin.server.AbstractExtension;
@@ -39,6 +36,9 @@ import com.vaadin.ui.AbstractComponent;
 public class DragSourceExtension<T extends AbstractComponent> extends
         AbstractExtension {
 
+    private Registration dragStartListenerHandle;
+    private Registration dragEndListenerHandle;
+
     /**
      * Extends {@code target} component and makes it a drag source.
      *
@@ -50,7 +50,7 @@ public class DragSourceExtension<T extends AbstractComponent> extends
             @Override
             public void dragStart() {
                 DragStartEvent<T> event = new DragStartEvent<>(target,
-                        getState(false).types, getState(false).data,
+                        getState(false).dataTransferText,
                         getState(false).effectAllowed);
                 fireEvent(event);
             }
@@ -58,13 +58,30 @@ public class DragSourceExtension<T extends AbstractComponent> extends
             @Override
             public void dragEnd() {
                 DragEndEvent<T> event = new DragEndEvent<>(target,
-                        getState(false).types, getState(false).data,
+                        getState(false).dataTransferText,
                         getState(false).effectAllowed);
                 fireEvent(event);
             }
         });
 
         super.extend(target);
+
+        // Set current extension as active drag source in the UI
+        dragStartListenerHandle = addDragStartListener(
+                event -> getUI().setActiveDragSource(this));
+
+        // Remove current extension as active drag source from the UI
+        dragEndListenerHandle = addDragEndListener(
+                event -> getUI().setActiveDragSource(null));
+    }
+
+    @Override
+    public void remove() {
+        super.remove();
+
+        // Remove listeners attached on construction
+        dragStartListenerHandle.remove();
+        dragEndListenerHandle.remove();
     }
 
     /**
@@ -100,89 +117,32 @@ public class DragSourceExtension<T extends AbstractComponent> extends
     }
 
     /**
-     * Sets the data for this drag source element. Used to set data for client
-     * side drag element using {@code DataTransfer.setData()}. To be used as a
-     * map, key-value pairs are stored. Order of entries are preserved.
-     * <p>
-     * Note that by HTML specification, the browser will change data type
-     * "{@code text}" to "{@code text/plain}" and "{@code url}" to "{@code
-     * text/uri-list}" during client side drag event.
+     * Sets data for this drag source element. The data is set for the client
+     * side draggable element using the {@code DataTransfer.setData("text",
+     * data)} method.
      *
-     * @param format
-     *         Data type to store, e.g. {@code text/plain} or {@code
-     *         text/uri-list}. Cannot be {@code null}.
      * @param data
-     *         Data to store for the data type. Cannot be {@code null}.
+     *         Data to be set for the client side draggable element.
      */
-    public void setTransferData(String format, String data) {
-        if (format == null) {
-            throw new IllegalArgumentException("Data type cannot be null");
-        }
-
-        if (data == null) {
-            throw new IllegalArgumentException("Data cannot be null");
-        }
-
-        if (!getState(false).types.contains(format)) {
-            getState().types.add(format);
-        }
-        getState().data.put(format, data);
+    public void setDataTransferText(String data) {
+        getState().dataTransferText = data;
     }
 
     /**
-     * Returns the data stored for {@code format} type in this drag source
+     * Returns the data stored with type {@code "text"} in this drag source
      * element.
      *
-     * @param format
-     *         Data type of the requested data, e.g. {@code text/plain} or
-     *         {@code text/uri-list}.
-     * @return Data that is stored for {@code format} data type.
+     * @return Data of type {@code "text"} stored in this drag source element.
      */
-    public String getTransferData(String format) {
-        return getState(false).data.get(format);
-    }
-
-    /**
-     * Returns the map of data stored in this drag source element. The returned
-     * map preserves the order of storage and is unmodifiable.
-     *
-     * @return Unmodifiable copy of the map of data in the order the data was
-     * stored.
-     */
-    public Map<String, String> getTransferData() {
-        Map<String, String> data = getState(false).data;
-
-        // Create a map of data that preserves the order of types
-        LinkedHashMap<String, String> orderedData = new LinkedHashMap<>(
-                data.size());
-        getState(false).types
-                .forEach(type -> orderedData.put(type, data.get(type)));
-
-        return Collections.unmodifiableMap(orderedData);
-    }
-
-    /**
-     * Clears data with the given type for this drag source element when
-     * present.
-     *
-     * @param format
-     *         Type of data to be cleared. Cannot be {@code null}.
-     */
-    public void clearTransferData(String format) {
-        if (format == null) {
-            throw new IllegalArgumentException("Data type cannot be null");
-        }
-
-        getState().types.remove(format);
-        getState().data.remove(format);
+    public String getDataTransferText() {
+        return getState(false).dataTransferText;
     }
 
     /**
-     * Clears all data for this drag source element.
+     * Clears data of type {@code "text"} in this drag source element.
      */
-    public void clearTransferData() {
-        getState().types.clear();
-        getState().data.clear();
+    public void clearDataTransferText() {
+        getState().dataTransferText = null;
     }
 
     /**
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 642f9b3b06..bfe1bc8c83 100644
--- a/server/src/main/java/com/vaadin/event/dnd/DragStartEvent.java
+++ b/server/src/main/java/com/vaadin/event/dnd/DragStartEvent.java
@@ -15,10 +15,6 @@
  */
 package com.vaadin.event.dnd;
 
-import java.util.LinkedHashMap;
-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;
@@ -35,7 +31,7 @@ import com.vaadin.ui.Component;
  */
 public class DragStartEvent<T extends AbstractComponent> extends
         Component.Event {
-    private final Map<String, String> data;
+    private final String dataTransferText;
     private final EffectAllowed effectAllowed;
 
     /**
@@ -43,35 +39,30 @@ public class DragStartEvent<T extends AbstractComponent> extends
      *
      * @param source
      *         Component that is dragged.
-     * @param types
-     *         List of data types from {@code DataTransfer.types} object.
-     * @param data
-     *         Map containing all types and corresponding data from the {@code
-     *         DataTransfer} object.
+     * @param dataTransferText
+     *         Data of type {@code "text"} from the {@code DataTransfer}
+     *         object.
      * @param effectAllowed
      *         Allowed effects from {@code DataTransfer.effectAllowed} object.
      */
-    public DragStartEvent(T source, List<String> types,
-            Map<String, String> data, EffectAllowed effectAllowed) {
+    public DragStartEvent(T source, String dataTransferText,
+            EffectAllowed effectAllowed) {
         super(source);
 
-        // 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.dataTransferText = dataTransferText;
 
         this.effectAllowed = effectAllowed;
     }
 
     /**
-     * Get data from the client side {@code DataTransfer} object.
+     * Get data of type {@code "text"} from the client side {@code DataTransfer}
+     * object.
      *
-     * @param format
-     *         Data format, e.g. {@code text/plain} or {@code text/uri-list}.
-     * @return Data for the given format if exists in the client side {@code
-     * DataTransfer}, otherwise {@code null}.
+     * @return Data of type {@code "text"} if exists in the client side {@code
+     * DataTransfer} object, otherwise {@literal null}.
      */
-    public String getTransferData(String format) {
-        return data != null ? data.get(format) : null;
+    public String getDataTransferText() {
+        return dataTransferText;
     }
 
     /**
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 433276550b..3fb655f176 100644
--- a/server/src/main/java/com/vaadin/event/dnd/DropEvent.java
+++ b/server/src/main/java/com/vaadin/event/dnd/DropEvent.java
@@ -15,9 +15,6 @@
  */
 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;
@@ -34,9 +31,9 @@ import com.vaadin.ui.Component;
  * @since 8.1
  */
 public class DropEvent<T extends AbstractComponent> extends Component.Event {
-    private final Map<String, String> data;
+    private final String dataTransferText;
     private final DropEffect dropEffect;
-    private final DragSourceExtension<AbstractComponent> dragSourceExtension;
+    private final DragSourceExtension<? extends AbstractComponent> dragSourceExtension;
     private final AbstractComponent dragSource;
 
     /**
@@ -44,25 +41,20 @@ public class DropEvent<T extends AbstractComponent> extends Component.Event {
      *
      * @param target
      *         Component that received the drop.
-     * @param types
-     *         List of data types from {@code DataTransfer.types} object.
-     * @param data
-     *         Map containing all types and corresponding data from the {@code
-     *         DataTransfer} object.
+     * @param dataTransferText
+     *         Data of type {@code "text"} from the {@code 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 target, List<String> types, Map<String, String> data,
-            DropEffect dropEffect,
-            DragSourceExtension<AbstractComponent> dragSourceExtension) {
+    public DropEvent(T target, String dataTransferText, DropEffect dropEffect,
+            DragSourceExtension<? extends 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.dataTransferText = dataTransferText;
 
         this.dropEffect = dropEffect;
 
@@ -72,15 +64,14 @@ public class DropEvent<T extends AbstractComponent> extends Component.Event {
     }
 
     /**
-     * Get data from the client side {@code DataTransfer} object.
+     * Get data of type {@code "text"} from the client side {@code DataTransfer}
+     * object.
      *
-     * @param format
-     *         Data format, e.g. {@code text/plain} or {@code text/uri-list}.
-     * @return Data for the given format if exists in the client side {@code
-     * DataTransfer}, otherwise {@code null}.
+     * @return Data of type {@code "text"} if exists in the client side {@code
+     * DataTransfer} object, otherwise {@literal null}.
      */
-    public String getTransferData(String format) {
-        return data != null ? data.get(format) : null;
+    public String getDataTransferText() {
+        return dataTransferText;
     }
 
     /**
@@ -110,7 +101,7 @@ public class DropEvent<T extends AbstractComponent> extends Component.Event {
      *
      * @return Drag source extension or an empty optional
      */
-    public Optional<DragSourceExtension<AbstractComponent>> getDragSourceExtension() {
+    public Optional<DragSourceExtension<? extends AbstractComponent>> getDragSourceExtension() {
         return Optional.ofNullable(dragSourceExtension);
     }
 
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 fd363573d1..2df43027a1 100644
--- a/server/src/main/java/com/vaadin/event/dnd/DropTargetExtension.java
+++ b/server/src/main/java/com/vaadin/event/dnd/DropTargetExtension.java
@@ -18,7 +18,6 @@ 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;
@@ -44,17 +43,9 @@ public class DropTargetExtension<T extends AbstractComponent> extends
      *         Component to be extended.
      */
     public DropTargetExtension(T target) {
-        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, dragSource);
+        registerRpc((DropTargetRpc) (dataTransferText, dropEffect) -> {
+            DropEvent<T> event = new DropEvent<>(target, dataTransferText,
+                    dropEffect, getUI().getActiveDragSource());
 
             fireEvent(event);
         });
diff --git a/server/src/main/java/com/vaadin/ui/UI.java b/server/src/main/java/com/vaadin/ui/UI.java
index 6341217e82..31de66c558 100644
--- a/server/src/main/java/com/vaadin/ui/UI.java
+++ b/server/src/main/java/com/vaadin/ui/UI.java
@@ -44,6 +44,7 @@ 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.navigator.Navigator;
 import com.vaadin.server.ClientConnector;
 import com.vaadin.server.ComponentSizeValidator;
@@ -295,6 +296,11 @@ public abstract class UI extends AbstractSingleComponentContainer
     private int lastProcessedClientToServerId = -1;
 
     /**
+     * Stores the extension of the active drag source component
+     */
+    private DragSourceExtension<? extends AbstractComponent> activeDragSource;
+
+    /**
      * Creates a new empty UI without a caption. The content of the UI must be
      * set by calling {@link #setContent(Component)} before using the UI.
      */
@@ -1803,6 +1809,31 @@ public abstract class UI extends AbstractSingleComponentContainer
     }
 
     /**
+     * Sets the drag source of an active HTML5 drag event.
+     *
+     * @param extension
+     *         Extension of the drag source component.
+     * @see DragSourceExtension
+     * @since
+     */
+    public void setActiveDragSource(
+            DragSourceExtension<? extends AbstractComponent> extension) {
+        this.activeDragSource = extension;
+    }
+
+    /**
+     * Gets the drag source of an active HTML5 drag event.
+     *
+     * @return Extension of the drag source component if the drag event is
+     * active and originated from this UI, {@literal null} otherwise.
+     * @see DragSourceExtension
+     * @since
+     */
+    public DragSourceExtension<? extends AbstractComponent> getActiveDragSource() {
+        return this.activeDragSource;
+    }
+
+    /**
      * Event which is fired when the ordering of the windows is updated.
      * <p>
      * The other way to listen window position for specific window is