Implement drag and drop reordering in General files list

CHANGELOG.md

@@ -17,6 +17,7 @@ We refer to [GitHub issues](https://github.com/JabRef/jabref/issues) by using `#
 - Added 'Filter All' and 'Filter None' buttons with corresponding functionality to Quality Check tool.
 - We increased the size of the keywords and file text areas in the entry editor
 - When the entry that is currently shown in the entry editor is deleted externally, the editor is now closed automatically [#2946](https://github.com/JabRef/jabref/issues/2946)
+- We added reordering of file and link entries in the `General`-Tab [3165, comment](https://github.com/JabRef/jabref/issues/3165#issuecomment-326269715)
 
 ### Fixed
 

src/main/java/org/jabref/gui/DragAndDropDataFormats.java

@@ -8,5 +8,6 @@
 public class DragAndDropDataFormats {
 
     public static final DataFormat GROUP = new DataFormat("dnd/org.jabref.model.groups.GroupTreeNode");
+    public static final DataFormat LINKED_FILE = new DataFormat("dnd/org.jabref.model.entry.LinkedFile");
     public static final DataFormat ENTRIES = new DataFormat("application/x-java-jvm-local-objectref");
 }

src/main/java/org/jabref/gui/fieldeditors/LinkedFilesEditor.java

@@ -3,6 +3,7 @@
 import java.util.Optional;
 
 import javafx.beans.binding.Bindings;
+import javafx.collections.ObservableList;
 import javafx.event.ActionEvent;
 import javafx.fxml.FXML;
 import javafx.scene.Node;
@@ -14,14 +15,19 @@
 import javafx.scene.control.ProgressBar;
 import javafx.scene.control.SeparatorMenuItem;
 import javafx.scene.control.Tooltip;
+import javafx.scene.input.ClipboardContent;
+import javafx.scene.input.DragEvent;
+import javafx.scene.input.Dragboard;
 import javafx.scene.input.KeyEvent;
 import javafx.scene.input.MouseButton;
 import javafx.scene.input.MouseEvent;
+import javafx.scene.input.TransferMode;
 import javafx.scene.layout.HBox;
 import javafx.scene.text.Text;
 
 import org.jabref.Globals;
 import org.jabref.gui.DialogService;
+import org.jabref.gui.DragAndDropDataFormats;
 import org.jabref.gui.autocompleter.AutoCompleteSuggestionProvider;
 import org.jabref.gui.keyboard.KeyBinding;
 import org.jabref.gui.util.ControlHelper;
@@ -31,6 +37,7 @@
 import org.jabref.logic.l10n.Localization;
 import org.jabref.model.database.BibDatabaseContext;
 import org.jabref.model.entry.BibEntry;
+import org.jabref.model.entry.LinkedFile;
 
 import de.jensd.fx.glyphs.materialdesignicons.MaterialDesignIcon;
 import de.jensd.fx.glyphs.materialdesignicons.utils.MaterialDesignIconFactory;
@@ -49,12 +56,67 @@ public LinkedFilesEditor(String fieldName, DialogService dialogService, BibDatab
                 .withTooltip(LinkedFileViewModel::getDescription)
                 .withGraphic(LinkedFilesEditor::createFileDisplay)
                 .withContextMenu(this::createContextMenuForFile)
-                .withOnMouseClickedEvent(this::handleItemMouseClick);
+                .withOnMouseClickedEvent(this::handleItemMouseClick)
+                .setOnDragDetected(this::handleOnDragDetected)
+                .setOnDragDropped(this::handleOnDragDropped)
+                .setOnDragOver(this::handleOnDragOver);
+
         listView.setCellFactory(cellFactory);
-        Bindings.bindContent(listView.itemsProperty().get(), viewModel.filesProperty());
+
+        Bindings.bindContentBidirectional(listView.itemsProperty().get(), viewModel.filesProperty());
         setUpKeyBindings();
     }
 
+    private void handleOnDragOver(LinkedFileViewModel originalItem, DragEvent event) {
+        if ((event.getGestureSource() != originalItem) && event.getDragboard().hasContent(DragAndDropDataFormats.LINKED_FILE)) {
+            event.acceptTransferModes(TransferMode.MOVE);
+        }
+    }
+
+    private void handleOnDragDetected(@SuppressWarnings("unused") LinkedFileViewModel linkedFile, MouseEvent event) {
+        LinkedFile selectedItem = listView.getSelectionModel().getSelectedItem().getFile();
+        if (selectedItem != null) {
+            ClipboardContent content = new ClipboardContent();
+            Dragboard dragboard = listView.startDragAndDrop(TransferMode.MOVE);
+            //We have to use the model class here, as the content of the dragboard must be serializable
+            content.put(DragAndDropDataFormats.LINKED_FILE, selectedItem);
+            dragboard.setContent(content);
+        }
+        event.consume();
+    }
+
+    private void handleOnDragDropped(LinkedFileViewModel originalItem, DragEvent event) {
+        Dragboard dragboard = event.getDragboard();
+        boolean success = false;
+
+        ObservableList<LinkedFileViewModel> items = listView.itemsProperty().get();
+
+        if (dragboard.hasContent(DragAndDropDataFormats.LINKED_FILE)) {
+
+            LinkedFile linkedFile = (LinkedFile) dragboard.getContent(DragAndDropDataFormats.LINKED_FILE);
+            LinkedFileViewModel transferedItem = null;
+            int draggedIdx = 0;
+            for (int i = 0; i < items.size(); i++) {
+                if (items.get(i).getFile().equals(linkedFile)) {
+                    draggedIdx = i;
+                    transferedItem = items.get(i);
+                    break;
+                }
+            }
+
+            int thisIdx = items.indexOf(originalItem);
+            items.set(draggedIdx, originalItem);
+            items.set(thisIdx, transferedItem);
+
+            event.setDropCompleted(success);
+            event.consume();
+            success = true;
+        }
+        event.setDropCompleted(success);
+        event.consume();
+
+    }
+
     private static Node createFileDisplay(LinkedFileViewModel linkedFile) {
         Text icon = MaterialDesignIconFactory.get().createIcon(linkedFile.getTypeIcon());
         Text text = new Text(linkedFile.getLink());
@@ -79,15 +141,15 @@ private void setUpKeyBindings() {
             Optional<KeyBinding> keyBinding = Globals.getKeyPrefs().mapToKeyBinding(event);
             if (keyBinding.isPresent()) {
                 switch (keyBinding.get()) {
-                case DELETE_ENTRY:
-                    LinkedFileViewModel selectedItem = listView.getSelectionModel().getSelectedItem();
-                    if (selectedItem != null) {
-                        viewModel.deleteFile(selectedItem);
-                    }
-                    event.consume();
-                    break;
-                default:
-                    // Pass other keys to children
+                    case DELETE_ENTRY:
+                        LinkedFileViewModel selectedItem = listView.getSelectionModel().getSelectedItem();
+                        if (selectedItem != null) {
+                            viewModel.deleteFile(selectedItem);
+                        }
+                        event.consume();
+                        break;
+                    default:
+                        // Pass other keys to children
                 }
             }
         });
@@ -160,6 +222,7 @@ private ContextMenu createContextMenuForFile(LinkedFileViewModel linkedFile) {
     }
 
     private void handleItemMouseClick(LinkedFileViewModel linkedFile, MouseEvent event) {
+
         if (event.getButton().equals(MouseButton.PRIMARY) && (event.getClickCount() == 2)) {
             // Double click -> edit
             linkedFile.edit();

src/main/java/org/jabref/gui/util/ViewModelListCellFactory.java

@@ -7,6 +7,7 @@
 import javafx.scene.control.ListCell;
 import javafx.scene.control.ListView;
 import javafx.scene.control.Tooltip;
+import javafx.scene.input.DragEvent;
 import javafx.scene.input.MouseEvent;
 import javafx.scene.paint.Paint;
 import javafx.scene.text.Text;
@@ -30,6 +31,11 @@ public class ViewModelListCellFactory<T> implements Callback<ListView<T>, ListCe
     private BiConsumer<T, ? super MouseEvent> toOnMouseClickedEvent;
     private Callback<T, String> toStyleClass;
     private Callback<T, ContextMenu> toContextMenu;
+    private BiConsumer<T, ? super MouseEvent> toOnDragDetected;
+    private BiConsumer<T, ? super DragEvent> toOnDragDropped;
+    private BiConsumer<T, ? super DragEvent> toOnDragEntered;
+    private BiConsumer<T, ? super DragEvent> toOnDragExited;
+    private BiConsumer<T, ? super DragEvent> toOnDragOver;
 
     public ViewModelListCellFactory<T> withText(Callback<T, String> toText) {
         this.toText = toText;
@@ -76,6 +82,31 @@ public ViewModelListCellFactory<T> withOnMouseClickedEvent(
         return this;
     }
 
+    public ViewModelListCellFactory<T> setOnDragDetected(BiConsumer<T, ? super MouseEvent> toOnDragDetected) {
+        this.toOnDragDetected = toOnDragDetected;
+        return this;
+    }
+
+    public ViewModelListCellFactory<T> setOnDragDropped(BiConsumer<T, ? super DragEvent> toOnDragDropped) {
+        this.toOnDragDropped = toOnDragDropped;
+        return this;
+    }
+
+    public ViewModelListCellFactory<T> setOnDragEntered(BiConsumer<T, ? super DragEvent> toOnDragEntered) {
+        this.toOnDragEntered = toOnDragEntered;
+        return this;
+    }
+
+    public ViewModelListCellFactory<T> setOnDragExited(BiConsumer<T, ? super DragEvent> toOnDragExited) {
+        this.toOnDragExited = toOnDragExited;
+        return this;
+    }
+
+    public ViewModelListCellFactory<T> setOnDragOver(BiConsumer<T, ? super DragEvent> toOnDragOver) {
+        this.toOnDragOver = toOnDragOver;
+        return this;
+    }
+
     @Override
     public ListCell<T> call(ListView<T> param) {
 
@@ -86,7 +117,7 @@ protected void updateItem(T item, boolean empty) {
                 super.updateItem(item, empty);
 
                 T viewModel = getItem();
-                if (empty || viewModel == null) {
+                if (empty || (viewModel == null)) {
                     setText(null);
                     setGraphic(null);
                     setOnMouseClicked(null);
@@ -113,6 +144,21 @@ protected void updateItem(T item, boolean empty) {
                     if (toContextMenu != null) {
                         setContextMenu(toContextMenu.call(viewModel));
                     }
+                    if (toOnDragDetected != null) {
+                        setOnDragDetected(event -> toOnDragDetected.accept(viewModel, event));
+                    }
+                    if (toOnDragDropped != null) {
+                        setOnDragDropped(event -> toOnDragDropped.accept(viewModel, event));
+                    }
+                    if (toOnDragEntered != null) {
+                        setOnDragEntered(event -> toOnDragEntered.accept(viewModel, event));
+                    }
+                    if (toOnDragExited != null) {
+                        setOnDragExited(event -> toOnDragExited.accept(viewModel, event));
+                    }
+                    if (toOnDragOver != null) {
+                        setOnDragOver(event -> toOnDragOver.accept(viewModel, event));
+                    }
                 }
                 getListView().refresh();
             }

src/main/java/org/jabref/model/entry/LinkedFile.java

@@ -1,5 +1,6 @@
 package org.jabref.model.entry;
 
+import java.io.Serializable;
 import java.net.URL;
 import java.nio.file.Path;
 import java.nio.file.Paths;
@@ -13,8 +14,9 @@
 
 /**
  * Represents the link to an external file (e.g. associated PDF file).
+ * This class is {@link Serializable} which is needed for drag and drop in gui
  */
-public class LinkedFile {
+public class LinkedFile implements Serializable {
 
     private static final LinkedFile NULL_OBJECT = new LinkedFile("", "", "");
     private String description;
@@ -26,6 +28,7 @@ public LinkedFile(String description, String link, String fileType) {
         this.link = Objects.requireNonNull(link);
         this.fileType = Objects.requireNonNull(fileType);
     }
+
     public LinkedFile(String description, URL link, String fileType) {
         this(description, Objects.requireNonNull(link).toString(), fileType);
     }