Add API for multiple drag data generators (#9321)

* Add ability to set multiple drag data generators for any drag data type
and change default to be accepted by spreadsheet applications such as Excel

2 files changed, 68 insertions, 52 deletions

diff --git a/client/src/main/java/com/vaadin/client/connectors/grid/GridDragSourceConnector.java b/client/src/main/java/com/vaadin/client/connectors/grid/GridDragSourceConnector.java
index 175383af87..1a96c1ea66 100644
--- a/client/src/main/java/com/vaadin/client/connectors/grid/GridDragSourceConnector.java
+++ b/client/src/main/java/com/vaadin/client/connectors/grid/GridDragSourceConnector.java
@@ -16,7 +16,11 @@
 package com.vaadin.client.connectors.grid;
 
 import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
 import java.util.List;
+import java.util.Map;
+import java.util.function.Function;
 import java.util.stream.Collectors;
 
 import com.google.gwt.animation.client.AnimationScheduler;
@@ -35,6 +39,7 @@ import com.vaadin.client.widget.escalator.RowContainer;
 import com.vaadin.client.widget.grid.selection.SelectionModel;
 import com.vaadin.client.widgets.Escalator;
 import com.vaadin.client.widgets.Grid;
+import com.vaadin.server.SerializableFunction;
 import com.vaadin.shared.Range;
 import com.vaadin.shared.ui.Connect;
 import com.vaadin.shared.ui.dnd.DragSourceState;
@@ -45,8 +50,6 @@ import com.vaadin.shared.ui.grid.GridState;
 import com.vaadin.ui.components.grid.GridDragSource;
 
 import elemental.events.Event;
-import elemental.json.Json;
-import elemental.json.JsonArray;
 import elemental.json.JsonObject;
 
 /**
@@ -199,10 +202,26 @@ public class GridDragSourceConnector extends DragSourceExtensionConnector {
     }
 
     @Override
-    protected String createDataTransferText(NativeEvent dragStartEvent) {
-        JsonArray dragData = toJsonArray(getDraggedRows(dragStartEvent).stream()
-                .map(this::getDragData).collect(Collectors.toList()));
-        return dragData.toJson();
+    protected Map<String, String> createDataTransferData(
+            NativeEvent dragStartEvent) {
+        Map<String, String> dataMap = super
+                .createDataTransferData(dragStartEvent);
+
+        // Add data provided by the generator functions
+        getDraggedRows(dragStartEvent).forEach(row -> {
+            Map<String, String> rowDragData = getRowDragData(row);
+            rowDragData.forEach((type, data) -> {
+                if (dataMap.containsKey(type)) {
+                    dataMap.put(type, data);
+                } else {
+                    // Separate data with new line character when multiple rows
+                    // are dragged
+                    dataMap.put(type, dataMap.get(type) + "\n" + data);
+                }
+            });
+        });
+
+        return dataMap;
     }
 
     @Override
@@ -309,31 +328,25 @@ public class GridDragSourceConnector extends DragSourceExtensionConnector {
     }
 
     /**
-     * Converts a list of {@link JsonObject}s to a {@link JsonArray}.
+     * Gets drag data provided by the generator functions.
      *
-     * @param objects
-     *            List of json objects.
-     * @return Json array containing all json objects.
+     * @param row
+     *         The row data.
+     * @return The generated drag data type mapped to the corresponding drag
+     * data. If there are no generator functions, returns an empty map.
      */
-    private JsonArray toJsonArray(List<JsonObject> objects) {
-        JsonArray array = Json.createArray();
-        for (int i = 0; i < objects.size(); i++) {
-            array.set(i, objects.get(i));
+    private Map<String, String> getRowDragData(JsonObject row) {
+        // Collect a map of data types and data that is provided by the
+        // generator functions set for this drag source
+        if (row.hasKey(GridDragSourceState.JSONKEY_DRAG_DATA)) {
+            JsonObject dragData = row
+                    .getObject(GridDragSourceState.JSONKEY_DRAG_DATA);
+            return Arrays.stream(dragData.keys()).collect(
+                    Collectors.toMap(Function.identity(), dragData::get));
         }
-        return array;
-    }
 
-    /**
-     * Gets drag data from the row data if exists or returns complete row data
-     * otherwise.
-     *
-     * @param row
-     *            Row data.
-     * @return Drag data if present or row data otherwise.
-     */
-    private JsonObject getDragData(JsonObject row) {
-        return row.hasKey(GridDragSourceState.JSONKEY_DRAG_DATA)
-                ? row.getObject(GridDragSourceState.JSONKEY_DRAG_DATA) : row;
+        // Otherwise return empty map
+        return Collections.emptyMap();
     }
 
     @Override
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 552ff151cd..7d79fb74dc 100644
--- a/client/src/main/java/com/vaadin/client/extensions/DragSourceExtensionConnector.java
+++ b/client/src/main/java/com/vaadin/client/extensions/DragSourceExtensionConnector.java
@@ -15,7 +15,7 @@
  */
 package com.vaadin.client.extensions;
 
-import java.util.List;
+import java.util.LinkedHashMap;
 import java.util.Map;
 
 import com.google.gwt.animation.client.AnimationScheduler;
@@ -185,27 +185,25 @@ public class DragSourceExtensionConnector extends AbstractExtensionConnector {
         // Set drag image
         setDragImage(nativeEvent);
 
-        // Set data parameters
-        List<String> types = getState().types;
-        Map<String, String> data = getState().data;
-        for (String type : types) {
-            nativeEvent.getDataTransfer().setData(type, data.get(type));
-        }
+        // Create drag data
+        Map<String, String> dataMap = createDataTransferData(nativeEvent);
 
-        // Always set something as the text data, or DnD won't work in FF !
-        String dataTransferText = createDataTransferText(nativeEvent);
-        if (dataTransferText == null) {
-            dataTransferText = "";
-        }
+        if (dataMap != null) {
+            // Always set something as the text data, or DnD won't work in FF !
+            dataMap.putIfAbsent(DragSourceState.DATA_TYPE_TEXT, "");
 
-        // Override data type "text" when storing special data is needed
-        nativeEvent.getDataTransfer()
-                .setData(DragSourceState.DATA_TYPE_TEXT, dataTransferText);
+            // Set data to the event's data transfer
+            dataMap.forEach((type, data) -> nativeEvent.getDataTransfer()
+                    .setData(type, data));
 
-        // Initiate firing server side dragstart event when there is a
-        // DragStartListener attached on the server side
-        if (hasEventListener(DragSourceState.EVENT_DRAGSTART)) {
-            sendDragStartEventToServer(nativeEvent);
+            // Initiate firing server side dragstart event when there is a
+            // DragStartListener attached on the server side
+            if (hasEventListener(DragSourceState.EVENT_DRAGSTART)) {
+                sendDragStartEventToServer(nativeEvent);
+            }
+        } else {
+            // If returned data map is null, cancel drag event
+            nativeEvent.preventDefault();
         }
 
         // Stop event bubbling
@@ -255,15 +253,20 @@ public class DragSourceExtensionConnector extends AbstractExtensionConnector {
     }
 
     /**
-     * Creates data of type {@code "text"} for the {@code DataTransfer} object
-     * of the given event.
+     * Creates the data map to be set as the {@code DataTransfer} object's data.
      *
      * @param dragStartEvent
-     *            Event to set the data for.
-     * @return Textual data to be set for the event or {@literal null}.
+     *         The drag start event
+     * @return The map from type to data, or {@code null} for not setting any
+     * data. Returning {@code null} will cancel the drag start.
      */
-    protected String createDataTransferText(NativeEvent dragStartEvent) {
-        return getState().data.get(DragSourceState.DATA_TYPE_TEXT);
+    protected Map<String, String> createDataTransferData(
+            NativeEvent dragStartEvent) {
+        Map<String, String> orderedData = new LinkedHashMap<>();
+        for (String type : getState().types) {
+            orderedData.put(type, getState().data.get(type));
+        }
+        return orderedData;
     }
 
     /**