org.eclipse.swt.dnd.DragSource.java Source code

Java tutorial

Introduction

Here is the source code for org.eclipse.swt.dnd.DragSource.java

Source

/*******************************************************************************
 * Copyright (c) 2000, 2017 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *     Lars Vogel <Lars.Vogel@vogella.com> - Bug 497807
 *******************************************************************************/
package org.eclipse.swt.dnd;

import org.eclipse.swt.*;
import org.eclipse.swt.graphics.*;
import org.eclipse.swt.internal.*;
import org.eclipse.swt.internal.cocoa.*;
import org.eclipse.swt.widgets.*;

/**
 *
 * <code>DragSource</code> defines the source object for a drag and drop transfer.
 *
 * <p>IMPORTANT: This class is <em>not</em> intended to be subclassed.</p>
 *
 * <p>A drag source is the object which originates a drag and drop operation. For the specified widget,
 * it defines the type of data that is available for dragging and the set of operations that can
 * be performed on that data.  The operations can be any bit-wise combination of DND.MOVE, DND.COPY or
 * DND.LINK.  The type of data that can be transferred is specified by subclasses of Transfer such as
 * TextTransfer or FileTransfer.  The type of data transferred can be a predefined system type or it
 * can be a type defined by the application.  For instructions on how to define your own transfer type,
 * refer to <code>ByteArrayTransfer</code>.</p>
 *
 * <p>You may have several DragSources in an application but you can only have one DragSource
 * per Control.  Data dragged from this DragSource can be dropped on a site within this application
 * or it can be dropped on another application such as an external Text editor.</p>
 *
 * <p>The application supplies the content of the data being transferred by implementing the
 * <code>DragSourceListener</code> and associating it with the DragSource via DragSource#addDragListener.</p>
 *
 * <p>When a successful move operation occurs, the application is required to take the appropriate
 * action to remove the data from its display and remove any associated operating system resources or
 * internal references.  Typically in a move operation, the drop target makes a copy of the data
 * and the drag source deletes the original.  However, sometimes copying the data can take a long
 * time (such as copying a large file).  Therefore, on some platforms, the drop target may actually
 * move the data in the operating system rather than make a copy.  This is usually only done in
 * file transfers.  In this case, the drag source is informed in the DragEnd event that a
 * DROP_TARGET_MOVE was performed.  It is the responsibility of the drag source at this point to clean
 * up its displayed information.  No action needs to be taken on the operating system resources.</p>
 *
 * <p> The following example shows a Label widget that allows text to be dragged from it.</p>
 *
 * <pre><code>
 *   // Enable a label as a Drag Source
 *   Label label = new Label(shell, SWT.NONE);
 *   // This example will allow text to be dragged
 *   Transfer[] types = new Transfer[] {TextTransfer.getInstance()};
 *   // This example will allow the text to be copied or moved to the drop target
 *   int operations = DND.DROP_MOVE | DND.DROP_COPY;
 *
 *   DragSource source = new DragSource(label, operations);
 *   source.setTransfer(types);
 *   source.addDragListener(new DragSourceListener() {
 *      public void dragStart(DragSourceEvent e) {
 *         // Only start the drag if there is actually text in the
 *         // label - this text will be what is dropped on the target.
 *         if (label.getText().length() == 0) {
 *            event.doit = false;
 *         }
 *      };
 *      public void dragSetData(DragSourceEvent event) {
 *         // A drop has been performed, so provide the data of the
 *         // requested type.
 *         // (Checking the type of the requested data is only
 *         // necessary if the drag source supports more than
 *         // one data type but is shown here as an example).
 *         if (TextTransfer.getInstance().isSupportedType(event.dataType)){
 *            event.data = label.getText();
 *         }
 *      }
 *      public void dragFinished(DragSourceEvent event) {
 *         // A Move operation has been performed so remove the data
 *         // from the source
 *         if (event.detail == DND.DROP_MOVE)
 *            label.setText("");
 *      }
 *   });
 * </code></pre>
 *
 *
 * <dl>
 *   <dt><b>Styles</b></dt> <dd>DND.DROP_NONE, DND.DROP_COPY, DND.DROP_MOVE, DND.DROP_LINK</dd>
 *   <dt><b>Events</b></dt> <dd>DND.DragStart, DND.DragSetData, DND.DragEnd</dd>
 * </dl>
 *
 * @see <a href="http://www.eclipse.org/swt/snippets/#dnd">Drag and Drop snippets</a>
 * @see <a href="http://www.eclipse.org/swt/examples.php">SWT Example: DNDExample</a>
 * @see <a href="http://www.eclipse.org/swt/">Sample code and further information</a>
 * @noextend This class is not intended to be subclassed by clients.
 */
@SuppressWarnings({ "rawtypes" })
public class DragSource extends Widget {

    // TODO: These should either move out of Display or be accessible to this class.
    static byte[] types = { '*', '\0' };
    static int size = C.PTR_SIZEOF, align = C.PTR_SIZEOF == 4 ? 2 : 3;

    static Callback dragSource2Args, dragSource3Args, dragSource4Args, dragSource5Args, dragSource6Args;
    static final byte[] SWT_OBJECT = { 'S', 'W', 'T', '_', 'O', 'B', 'J', 'E', 'C', 'T', '\0' };
    static long proc2 = 0, proc3 = 0, proc4 = 0, proc5 = 0, proc6 = 0;

    String paths[];
    boolean exist[];

    static {
        String className = "SWTDragSourceDelegate";

        Class clazz = DragSource.class;

        dragSource2Args = new Callback(clazz, "dragSourceProc", 2);
        proc2 = dragSource2Args.getAddress();
        if (proc2 == 0)
            SWT.error(SWT.ERROR_NO_MORE_CALLBACKS);

        dragSource3Args = new Callback(clazz, "dragSourceProc", 3);
        proc3 = dragSource3Args.getAddress();
        if (proc3 == 0)
            SWT.error(SWT.ERROR_NO_MORE_CALLBACKS);

        dragSource4Args = new Callback(clazz, "dragSourceProc", 4);
        proc4 = dragSource4Args.getAddress();
        if (proc4 == 0)
            SWT.error(SWT.ERROR_NO_MORE_CALLBACKS);

        dragSource5Args = new Callback(clazz, "dragSourceProc", 5);
        proc5 = dragSource5Args.getAddress();
        if (proc5 == 0)
            SWT.error(SWT.ERROR_NO_MORE_CALLBACKS);

        dragSource6Args = new Callback(clazz, "dragSourceProc", 6);
        proc6 = dragSource6Args.getAddress();
        if (proc6 == 0)
            SWT.error(SWT.ERROR_NO_MORE_CALLBACKS);

        long cls = OS.objc_allocateClassPair(OS.class_NSObject, className, 0);
        OS.class_addIvar(cls, SWT_OBJECT, size, (byte) align, types);

        long draggedImage_endedAt_operationProc = OS.CALLBACK_draggedImage_endedAt_operation_(proc5);

        // Add the NSDraggingSource callbacks
        OS.class_addMethod(cls, OS.sel_draggingSourceOperationMaskForLocal_, proc3, "@:I");
        OS.class_addMethod(cls, OS.sel_draggedImage_beganAt_, proc4, "@:@{NSPoint=ff}");
        OS.class_addMethod(cls, OS.sel_draggedImage_endedAt_operation_, draggedImage_endedAt_operationProc,
                "@:@{NSPoint=ff}I");
        OS.class_addMethod(cls, OS.sel_ignoreModifierKeysWhileDragging, proc3, "@:");

        // Add the NSPasteboard delegate callback
        OS.class_addMethod(cls, OS.sel_pasteboard_provideDataForType_, proc4, "@:@@");

        OS.objc_registerClassPair(cls);
    }

    // info for registering as a drag source
    Control control;
    Listener controlListener;
    Transfer[] transferAgents = new Transfer[0];
    DragSourceEffect dragEffect;
    Image dragImageFromListener;
    private int dragOperations;
    SWTDragSourceDelegate dragSourceDelegate;

    static final String DEFAULT_DRAG_SOURCE_EFFECT = "DEFAULT_DRAG_SOURCE_EFFECT"; //$NON-NLS-1$

    private long delegateJniRef;
    private Point dragOffset;

    /**
     * Creates a new <code>DragSource</code> to handle dragging from the specified <code>Control</code>.
     * Creating an instance of a DragSource may cause system resources to be allocated depending on the platform.
     * It is therefore mandatory that the DragSource instance be disposed when no longer required.
     *
     * @param control the <code>Control</code> that the user clicks on to initiate the drag
     * @param style the bitwise OR'ing of allowed operations; this may be a combination of any of
     *               DND.DROP_NONE, DND.DROP_COPY, DND.DROP_MOVE, DND.DROP_LINK
     *
     * @exception SWTException <ul>
     *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the parent</li>
     *    <li>ERROR_INVALID_SUBCLASS - if this class is not an allowed subclass</li>
     * </ul>
     * @exception SWTError <ul>
     *    <li>ERROR_CANNOT_INIT_DRAG - unable to initiate drag source; this will occur if more than one
     *        drag source is created for a control or if the operating system will not allow the creation
     *        of the drag source</li>
     * </ul>
     *
     * <p>NOTE: ERROR_CANNOT_INIT_DRAG should be an SWTException, since it is a
     * recoverable error, but can not be changed due to backward compatibility.</p>
     *
     * @see Widget#dispose
     * @see DragSource#checkSubclass
     * @see DND#DROP_NONE
     * @see DND#DROP_COPY
     * @see DND#DROP_MOVE
     * @see DND#DROP_LINK
     */
    public DragSource(Control control, int style) {
        super(control, checkStyle(style));
        this.control = control;
        if (control.getData(DND.DRAG_SOURCE_KEY) != null) {
            DND.error(DND.ERROR_CANNOT_INIT_DRAG);
        }
        control.setData(DND.DRAG_SOURCE_KEY, this);

        controlListener = event -> {
            if (event.type == SWT.Dispose) {
                if (!DragSource.this.isDisposed()) {
                    DragSource.this.dispose();
                }
            }
            if (event.type == SWT.DragDetect) {
                if (!DragSource.this.isDisposed()) {
                    if (event.widget instanceof Table || event.widget instanceof Tree) {
                        DragSource.this.dragOutlineViewStart(event);
                    } else {
                        DragSource.this.drag(event);
                    }
                }
            }
        };
        control.addListener(SWT.Dispose, controlListener);
        control.addListener(SWT.DragDetect, controlListener);

        this.addListener(SWT.Dispose, e -> onDispose());

        Object effect = control.getData(DEFAULT_DRAG_SOURCE_EFFECT);
        if (effect instanceof DragSourceEffect) {
            dragEffect = (DragSourceEffect) effect;
        } else if (control instanceof Tree) {
            dragEffect = new TreeDragSourceEffect((Tree) control);
        } else if (control instanceof Table) {
            dragEffect = new TableDragSourceEffect((Table) control);
        }

        delegateJniRef = OS.NewGlobalRef(this);
        if (delegateJniRef == 0)
            SWT.error(SWT.ERROR_NO_HANDLES);

        // The dragSourceDelegate implements the pasteboard callback to provide the dragged data, so we always need
        // to create it. NSDraggingSource methods are ignored in the table and tree case.
        dragSourceDelegate = (SWTDragSourceDelegate) new SWTDragSourceDelegate().alloc().init();
        OS.object_setInstanceVariable(dragSourceDelegate.id, SWT_OBJECT, delegateJniRef);

        // Tables and trees already implement dragging, so we need to override their drag methods instead of creating a dragging source.
        if (control instanceof Tree || control instanceof Table) {
            long cls = OS.object_getClass(control.view.id);

            if (cls == 0) {
                DND.error(DND.ERROR_CANNOT_INIT_DRAG);
            }

            // If we already added it, no need to do it again.
            long procPtr = OS.class_getMethodImplementation(cls, OS.sel_draggingSourceOperationMaskForLocal_);
            if (procPtr == proc3)
                return;

            long draggedImage_endedAt_operationProc = OS.CALLBACK_draggedImage_endedAt_operation_(proc5);

            // Add the NSDraggingSource overrides.
            OS.class_addMethod(cls, OS.sel_draggingSourceOperationMaskForLocal_, proc3, "@:I");
            OS.class_addMethod(cls, OS.sel_draggedImage_beganAt_, proc4, "@:@{NSPoint=ff}");
            OS.class_addMethod(cls, OS.sel_draggedImage_endedAt_operation_, draggedImage_endedAt_operationProc,
                    "@:@{NSPoint=ff}I");
            OS.class_addMethod(cls, OS.sel_ignoreModifierKeysWhileDragging, proc3, "@:");

            // Override to return the drag effect's image.
            OS.class_addMethod(cls, OS.sel_dragImageForRowsWithIndexes_tableColumns_event_offset_, proc6,
                    "@:@@@^NSPoint");
        }

    }

    /**
     * Adds the listener to the collection of listeners who will
     * be notified when a drag and drop operation is in progress, by sending
     * it one of the messages defined in the <code>DragSourceListener</code>
     * interface.
     *
     * <ul>
     * <li><code>dragStart</code> is called when the user has begun the actions required to drag the widget.
     * This event gives the application the chance to decide if a drag should be started.
     * <li><code>dragSetData</code> is called when the data is required from the drag source.
     * <li><code>dragFinished</code> is called when the drop has successfully completed (mouse up
     * over a valid target) or has been terminated (such as hitting the ESC key). Perform cleanup
     * such as removing data from the source side on a successful move operation.
     * </ul>
     *
     * @param listener the listener which should be notified
     *
     * @exception IllegalArgumentException <ul>
     *    <li>ERROR_NULL_ARGUMENT - if the listener is null</li>
     * </ul>
     * @exception SWTException <ul>
     *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
     *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
     * </ul>
     *
     * @see DragSourceListener
     * @see #getDragListeners
     * @see #removeDragListener
     * @see DragSourceEvent
     */
    public void addDragListener(DragSourceListener listener) {
        if (listener == null)
            DND.error(SWT.ERROR_NULL_ARGUMENT);
        DNDListener typedListener = new DNDListener(listener);
        typedListener.dndWidget = this;
        addListener(DND.DragStart, typedListener);
        addListener(DND.DragSetData, typedListener);
        addListener(DND.DragEnd, typedListener);
    }

    void dndCallSuper(long id, long sel, long arg0, NSPoint arg1, long arg2) {
        objc_super super_struct = new objc_super();
        super_struct.receiver = id;
        super_struct.super_class = OS.objc_msgSend(id, OS.sel_superclass);
        OS.objc_msgSendSuper(super_struct, sel, arg0, arg1, arg2);
    }

    void dndCallSuper(long id, long sel, long arg0, long arg1) {
        objc_super super_struct = new objc_super();
        super_struct.receiver = id;
        super_struct.super_class = OS.objc_msgSend(id, OS.sel_superclass);
        OS.objc_msgSendSuper(super_struct, sel, arg0, arg1);
    }

    long dndCallSuperObject(long id, long sel, long arg0, long arg1, long arg2, long arg3) {
        objc_super super_struct = new objc_super();
        super_struct.receiver = id;
        super_struct.super_class = OS.objc_msgSend(id, OS.sel_superclass);
        return OS.objc_msgSendSuper(super_struct, sel, arg0, arg1, arg2, arg3);
    }

    @Override
    protected void checkSubclass() {
        String name = getClass().getName();
        String validName = DragSource.class.getName();
        if (!validName.equals(name)) {
            DND.error(SWT.ERROR_INVALID_SUBCLASS);
        }
    }

    static int checkStyle(int style) {
        if (style == SWT.NONE)
            return DND.DROP_MOVE;
        return style;
    }

    void drag(Event dragDetectEvent) {

        DNDEvent event = startDrag(dragDetectEvent);
        if (event == null)
            return;

        // Start the drag here from the Control's view.
        NSEvent currEvent = NSApplication.sharedApplication().currentEvent();
        NSPoint pt = currEvent.locationInWindow();
        NSPoint viewPt = control.view.convertPoint_fromView_(pt, null);

        // Get the image for the drag. The drag should happen from the middle of the image.
        NSImage dragImage = null;
        Image defaultDragImage = null;
        try {
            Image image = event.image;

            // If no image was provided, just create a trivial image. dragImage requires a non-null image.
            if (image == null) {
                int width = 20, height = 20;
                Image newDragImage = new Image(Display.getCurrent(), width, height);
                GC imageGC = new GC(newDragImage);
                Color grayColor = new Color(Display.getCurrent(), 50, 50, 50);
                imageGC.setForeground(grayColor);
                imageGC.drawRectangle(0, 0, 19, 19);
                imageGC.dispose();
                ImageData newImageData = newDragImage.getImageData();
                newImageData.alpha = (int) (255 * .4);
                defaultDragImage = new Image(Display.getCurrent(), newImageData);
                newDragImage.dispose();
                grayColor.dispose();
                image = defaultDragImage;
                event.offsetX = width / 2;
                event.offsetY = height / 2;
            }

            dragImage = image.handle;

            NSSize imageSize = dragImage.size();
            viewPt.x -= event.offsetX;

            if (control.view.isFlipped())
                viewPt.y += imageSize.height - event.offsetY;
            else
                viewPt.y -= event.offsetY;

            // The third argument to dragImage is ignored as of 10.4.
            NSSize ignored = new NSSize();

            control.view.dragImage(dragImage, viewPt, ignored, NSApplication.sharedApplication().currentEvent(),
                    NSPasteboard.pasteboardWithName(OS.NSDragPboard), dragSourceDelegate, true);

        } finally {
            if (defaultDragImage != null)
                defaultDragImage.dispose();
        }
    }

    void dragOutlineViewStart(Event dragDetectEvent) {
        DNDEvent event = startDrag(dragDetectEvent);
        if (event == null)
            return;

        // Save off the custom image, if any.
        dragImageFromListener = event.image;

        // Save the computed offset for the image.  This needs to be passed back in dragImageForRowsWithIndexes
        // so the proxy image originates from the selection and not centered under the mouse.
        dragOffset = new Point(event.offsetX, event.offsetY);
    }

    void draggedImage_beganAt(long id, long sel, long arg0, long arg1) {
        if (new NSObject(id).isKindOfClass(OS.class_NSTableView)) {
            dndCallSuper(id, sel, arg0, arg1);
        }
    }

    void draggedImage_endedAt_operation(long id, long sel, long arg0, NSPoint arg1, long arg2) {
        int swtOperation = osOpToOp(arg2);
        if (paths != null) {
            NSFileManager fileManager = NSFileManager.defaultManager();
            for (int i = 0; i < paths.length; i++) {
                if (paths[i] != null && exist[i]) {
                    if (!fileManager.fileExistsAtPath(NSString.stringWith(paths[i]))) {
                        swtOperation &= ~DND.DROP_MOVE;
                        swtOperation |= DND.DROP_TARGET_MOVE;
                    }
                }
            }
            paths = null;
            exist = null;
        }
        OS.objc_msgSend(id, OS.sel_retain);
        try {
            Event event = new DNDEvent();
            event.widget = this;
            event.time = (int) System.currentTimeMillis();
            event.doit = swtOperation != DND.DROP_NONE;
            event.detail = swtOperation;
            notifyListeners(DND.DragEnd, event);
            dragImageFromListener = null;

            if (new NSObject(id).isKindOfClass(OS.class_NSTableView)) {
                dndCallSuper(id, sel, arg0, arg1, arg2);
            }
        } finally {
            OS.objc_msgSend(id, OS.sel_release);
        }
    }

    long dragImageForRowsWithIndexes_tableColumns_event_offset(long id, long sel, long arg0, long arg1, long arg2,
            long arg3) {
        if (dragImageFromListener != null) {
            NSPoint point = new NSPoint();
            point.x = dragOffset.x;
            point.y = dragOffset.y;
            OS.memmove(arg3, point, NSPoint.sizeof);
            return dragImageFromListener.handle.id;
        } else {
            return dndCallSuperObject(id, sel, arg0, arg1, arg2, arg3);
        }
    }

    /**
     * Cocoa NSDraggingSource implementations
     */
    long draggingSourceOperationMaskForLocal(long id, long sel, long arg0) {
        // Drag operations are same for local or remote drags.
        return dragOperations;
    }

    static long dragSourceProc(long id, long sel) {
        Display display = Display.findDisplay(Thread.currentThread());
        if (display == null || display.isDisposed())
            return 0;
        Widget widget = display.findWidget(id);
        if (widget == null)
            return 0;
        DragSource ds = null;

        if (widget instanceof DragSource) {
            ds = (DragSource) widget;
        } else {
            ds = (DragSource) widget.getData(DND.DRAG_SOURCE_KEY);
        }

        if (ds == null)
            return 0;

        if (sel == OS.sel_ignoreModifierKeysWhileDragging) {
            return (ds.ignoreModifierKeysWhileDragging(id, sel) ? 1 : 0);
        }

        return 0;
    }

    static long dragSourceProc(long id, long sel, long arg0) {
        Display display = Display.findDisplay(Thread.currentThread());
        if (display == null || display.isDisposed())
            return 0;
        Widget widget = display.findWidget(id);
        if (widget == null)
            return 0;
        DragSource ds = null;

        if (widget instanceof DragSource) {
            ds = (DragSource) widget;
        } else {
            ds = (DragSource) widget.getData(DND.DRAG_SOURCE_KEY);
        }

        if (ds == null)
            return 0;

        if (sel == OS.sel_draggingSourceOperationMaskForLocal_) {
            return ds.draggingSourceOperationMaskForLocal(id, sel, arg0);
        }

        return 0;
    }

    static long dragSourceProc(long id, long sel, long arg0, long arg1) {
        Display display = Display.findDisplay(Thread.currentThread());
        if (display == null || display.isDisposed())
            return 0;
        Widget widget = display.findWidget(id);
        if (widget == null)
            return 0;
        DragSource ds = null;

        if (widget instanceof DragSource) {
            ds = (DragSource) widget;
        } else {
            ds = (DragSource) widget.getData(DND.DRAG_SOURCE_KEY);
        }

        if (ds == null)
            return 0;

        if (sel == OS.sel_draggedImage_beganAt_) {
            ds.draggedImage_beganAt(id, sel, arg0, arg1);
        } else if (sel == OS.sel_pasteboard_provideDataForType_) {
            ds.pasteboard_provideDataForType(id, sel, arg0, arg1);
        }

        return 0;
    }

    static long dragSourceProc(long id, long sel, long arg0, long arg1, long arg2) {
        Display display = Display.findDisplay(Thread.currentThread());
        if (display == null || display.isDisposed())
            return 0;
        Widget widget = display.findWidget(id);
        if (widget == null)
            return 0;
        DragSource ds = null;

        if (widget instanceof DragSource) {
            ds = (DragSource) widget;
        } else {
            ds = (DragSource) widget.getData(DND.DRAG_SOURCE_KEY);
        }

        if (ds == null)
            return 0;

        if (sel == OS.sel_draggedImage_endedAt_operation_) {
            NSPoint point = new NSPoint();
            OS.memmove(point, arg1, NSPoint.sizeof);
            ds.draggedImage_endedAt_operation(id, sel, arg0, point, arg2);
        }

        return 0;
    }

    static long dragSourceProc(long id, long sel, long arg0, long arg1, long arg2, long arg3) {
        Display display = Display.findDisplay(Thread.currentThread());
        if (display == null || display.isDisposed())
            return 0;
        Widget widget = display.findWidget(id);
        if (widget == null)
            return 0;
        DragSource ds = null;

        if (widget instanceof DragSource) {
            ds = (DragSource) widget;
        } else {
            ds = (DragSource) widget.getData(DND.DRAG_SOURCE_KEY);
        }

        if (ds == null)
            return 0;

        if (sel == OS.sel_dragImageForRowsWithIndexes_tableColumns_event_offset_) {
            return ds.dragImageForRowsWithIndexes_tableColumns_event_offset(id, sel, arg0, arg1, arg2, arg3);
        }

        return 0;
    }

    /**
     * Returns the Control which is registered for this DragSource.  This is the control that the
     * user clicks in to initiate dragging.
     *
     * @return the Control which is registered for this DragSource
     */
    public Control getControl() {
        return control;
    }

    /**
     * Returns an array of listeners who will be notified when a drag and drop
     * operation is in progress, by sending it one of the messages defined in
     * the <code>DragSourceListener</code> interface.
     *
     * @return the listeners who will be notified when a drag and drop
     * operation is in progress
     *
     * @exception SWTException <ul>
     *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
     *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
     * </ul>
     *
     * @see DragSourceListener
     * @see #addDragListener
     * @see #removeDragListener
     * @see DragSourceEvent
     *
     * @since 3.4
     */
    public DragSourceListener[] getDragListeners() {
        Listener[] listeners = getListeners(DND.DragStart);
        int length = listeners.length;
        DragSourceListener[] dragListeners = new DragSourceListener[length];
        int count = 0;
        for (int i = 0; i < length; i++) {
            Listener listener = listeners[i];
            if (listener instanceof DNDListener) {
                dragListeners[count] = (DragSourceListener) ((DNDListener) listener).getEventListener();
                count++;
            }
        }
        if (count == length)
            return dragListeners;
        DragSourceListener[] result = new DragSourceListener[count];
        System.arraycopy(dragListeners, 0, result, 0, count);
        return result;
    }

    /**
     * Returns the drag effect that is registered for this DragSource.  This drag
     * effect will be used during a drag and drop operation.
     *
     * @return the drag effect that is registered for this DragSource
     *
     * @since 3.3
     */
    public DragSourceEffect getDragSourceEffect() {
        return dragEffect;
    }

    /**
     * Returns the list of data types that can be transferred by this DragSource.
     *
     * @return the list of data types that can be transferred by this DragSource
     */
    public Transfer[] getTransfer() {
        return transferAgents;
    }

    /**
     * We always want the modifier keys to potentially update the drag.
     */
    boolean ignoreModifierKeysWhileDragging(long id, long sel) {
        return false;
    }

    void onDispose() {
        if (control == null)
            return;

        if (controlListener != null) {
            control.removeListener(SWT.Dispose, controlListener);
            control.removeListener(SWT.DragDetect, controlListener);
        }
        controlListener = null;
        control.setData(DND.DRAG_SOURCE_KEY, null);
        control = null;
        transferAgents = null;

        if (delegateJniRef != 0)
            OS.DeleteGlobalRef(delegateJniRef);
        delegateJniRef = 0;

        if (dragSourceDelegate != null) {
            OS.object_setInstanceVariable(dragSourceDelegate.id, SWT_OBJECT, 0);
            dragSourceDelegate.release();
        }
    }

    int opToOsOp(int operation) {
        int osOperation = 0;
        if ((operation & DND.DROP_COPY) != 0) {
            osOperation |= OS.NSDragOperationCopy;
        }
        if ((operation & DND.DROP_LINK) != 0) {
            osOperation |= OS.NSDragOperationLink;
        }
        if ((operation & DND.DROP_MOVE) != 0) {
            osOperation |= OS.NSDragOperationMove;
        }
        if ((operation & DND.DROP_TARGET_MOVE) != 0) {
            osOperation |= OS.NSDragOperationDelete;
        }
        return osOperation;
    }

    int osOpToOp(long osOperation) {
        int operation = 0;
        if ((osOperation & OS.NSDragOperationCopy) != 0) {
            operation |= DND.DROP_COPY;
        }
        if ((osOperation & OS.NSDragOperationLink) != 0) {
            operation |= DND.DROP_LINK;
        }
        if ((osOperation & OS.NSDragOperationDelete) != 0) {
            operation |= DND.DROP_TARGET_MOVE;
        }
        if ((osOperation & OS.NSDragOperationMove) != 0) {
            operation |= DND.DROP_MOVE;
        }
        if (osOperation == OS.NSDragOperationEvery) {
            operation = DND.DROP_COPY | DND.DROP_MOVE | DND.DROP_LINK;
        }
        return operation;
    }

    void pasteboard_provideDataForType(long id, long sel, long arg0, long arg1) {
        NSPasteboard pasteboard = new NSPasteboard(arg0);
        NSString dataType = new NSString(arg1);
        if (pasteboard == null || dataType == null)
            return;
        TransferData transferData = new TransferData();
        transferData.type = Transfer.registerType(dataType.getString());
        DNDEvent event = new DNDEvent();
        event.widget = this;
        event.time = (int) System.currentTimeMillis();
        event.dataType = transferData;
        notifyListeners(DND.DragSetData, event);
        if (!event.doit)
            return;
        Transfer transfer = null;
        for (int i = 0; i < transferAgents.length; i++) {
            Transfer transferAgent = transferAgents[i];
            if (transferAgent != null && transferAgent.isSupportedType(transferData)) {
                transfer = transferAgent;
                break;
            }
        }
        if (transfer == null)
            return;
        transfer.javaToNative(event.data, transferData);
        if (transferData.data == null)
            return;

        NSObject tdata = transferData.data;

        if (dataType.isEqual(OS.NSPasteboardTypeString) || dataType.isEqual(OS.NSPasteboardTypeHTML)
                || dataType.isEqual(OS.NSPasteboardTypeRTF)) {
            pasteboard.setString((NSString) tdata, dataType);
        } else if (dataType.isEqual(OS.NSURLPboardType) || dataType.isEqual(OS.kUTTypeURL)) {
            NSURL url = (NSURL) tdata;
            pasteboard.writeObjects(NSArray.arrayWithObject(url));
        } else if (dataType.isEqual(OS.NSFilenamesPboardType) || dataType.isEqual(OS.kUTTypeFileURL)) {
            NSArray array = (NSArray) transferData.data;
            int count = (int) array.count();
            paths = new String[count];
            exist = new boolean[count];
            NSFileManager fileManager = NSFileManager.defaultManager();
            for (int i = 0; i < count; i++) {
                NSString filePath = new NSString(array.objectAtIndex(i));
                paths[i] = filePath.getString();
                exist[i] = fileManager.fileExistsAtPath(filePath);
            }
            pasteboard.setPropertyList((NSArray) tdata, OS.NSFilenamesPboardType);
        } else {
            pasteboard.setData((NSData) tdata, dataType);
        }
    }

    /**
     * Removes the listener from the collection of listeners who will
     * be notified when a drag and drop operation is in progress.
     *
     * @param listener the listener which should no longer be notified
     *
     * @exception IllegalArgumentException <ul>
     *    <li>ERROR_NULL_ARGUMENT - if the listener is null</li>
     * </ul>
     * @exception SWTException <ul>
     *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
     *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
     * </ul>
     *
     * @see DragSourceListener
     * @see #addDragListener
     * @see #getDragListeners
     */
    public void removeDragListener(DragSourceListener listener) {
        if (listener == null)
            DND.error(SWT.ERROR_NULL_ARGUMENT);
        removeListener(DND.DragStart, listener);
        removeListener(DND.DragSetData, listener);
        removeListener(DND.DragEnd, listener);
    }

    /**
     * Specifies the drag effect for this DragSource.  This drag effect will be
     * used during a drag and drop operation.
     *
     * @param effect the drag effect that is registered for this DragSource
     *
     * @since 3.3
     */
    public void setDragSourceEffect(DragSourceEffect effect) {
        dragEffect = effect;
    }

    /**
     * Specifies the list of data types that can be transferred by this DragSource.
     * The application must be able to provide data to match each of these types when
     * a successful drop has occurred.
     *
     * @param transferAgents a list of Transfer objects which define the types of data that can be
     * dragged from this source
     */
    public void setTransfer(Transfer... transferAgents) {
        this.transferAgents = transferAgents;
    }

    DNDEvent startDrag(Event dragEvent) {
        DNDEvent event = new DNDEvent();
        event.widget = this;
        event.x = dragEvent.x;
        event.y = dragEvent.y;
        event.time = dragEvent.time;
        event.doit = true;
        notifyListeners(DND.DragStart, event);
        if (!event.doit || transferAgents == null || transferAgents.length == 0)
            return null;

        NSPasteboard dragBoard = NSPasteboard.pasteboardWithName(OS.NSDragPboard);
        NSMutableArray nativeTypeArray = NSMutableArray.arrayWithCapacity(10);

        for (int i = 0; i < transferAgents.length; i++) {
            Transfer transfer = transferAgents[i];
            if (transfer != null) {
                String[] typeNames = transfer.getTypeNames();

                for (int j = 0; j < typeNames.length; j++) {
                    nativeTypeArray.addObject(NSString.stringWith(typeNames[j]));
                }
            }
        }
        dragBoard.declareTypes(nativeTypeArray, dragSourceDelegate);

        // Save off the drag operations -- AppKit will call back to us to request them during the drag.
        dragOperations = opToOsOp(getStyle());

        return event;
    }
}