/*******************************************************************************
* Copyright (c) 2000, 2015 IBM Corporation and others.
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Contributors:
* IBM Corporation - initial API and implementation
*******************************************************************************/
package org.eclipse.jface.util;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import org.eclipse.swt.dnd.DND;
import org.eclipse.swt.dnd.DropTargetEvent;
import org.eclipse.swt.dnd.DropTargetListener;
import org.eclipse.swt.dnd.Transfer;
import org.eclipse.swt.dnd.TransferData;
/**
* A <code>DelegatingDropAdapter</code> is a <code>DropTargetListener</code> that
* maintains and delegates to a set of {@link TransferDropTargetListener}s. Each
* <code>TransferDropTargetListener</code> can then be implemented as if it were
* the DropTarget's only <code>DropTargetListener</code>.
* <p>
* On <code>dragEnter</code>, <code>dragOperationChanged</code>, <code>dragOver</code>
* and <code>drop</code>, a <i>current</i> listener is obtained from the set of all
* <code>TransferDropTargetListeners</code>. The current listener is the first listener
* to return <code>true</code> for
* {@link TransferDropTargetListener#isEnabled(DropTargetEvent)}.
* The current listener is forwarded all <code>DropTargetEvents</code> until some other
* listener becomes the current listener, or the drop terminates.
* </p>
* <p>
* After adding all <code>TransferDropTargetListeners</code> to the
* <code>DelegatingDropAdapter</code> the combined set of <code>Transfers</code> should
* be set in the SWT <code>DropTarget</code>. <code>#getTransfers()</code> provides the
* set of <code>Transfer</code> types of all <code>TransferDropTargetListeners</code>.
* </p>
* <p>
* The following example snippet shows a <code>DelegatingDropAdapter</code> with two
* <code>TransferDropTargetListeners</code>. One supports dropping resources and
* demonstrates how a listener can be disabled in the isEnabled method.
* The other listener supports text transfer.
* </p>
* <code><pre>
* final TreeViewer viewer = new TreeViewer(shell, SWT.NONE);
* DelegatingDropAdapter dropAdapter = new DelegatingDropAdapter();
* dropAdapter.addDropTargetListener(new TransferDropTargetListener() {
* public Transfer getTransfer() {
* return ResourceTransfer.getInstance();
* }
* public boolean isEnabled(DropTargetEvent event) {
* // disable drop listener if there is no viewer selection
* if (viewer.getSelection().isEmpty())
* return false;
* return true;
* }
* public void dragEnter(DropTargetEvent event) {}
* public void dragLeave(DropTargetEvent event) {}
* public void dragOperationChanged(DropTargetEvent event) {}
* public void dragOver(DropTargetEvent event) {}
* public void drop(DropTargetEvent event) {
* if (event.data == null)
* return;
* IResource[] resources = (IResource[]) event.data;
* if (event.detail == DND.DROP_COPY) {
* // copy resources
* } else {
* // move resources
* }
*
* }
* public void dropAccept(DropTargetEvent event) {}
* });
* dropAdapter.addDropTargetListener(new TransferDropTargetListener() {
* public Transfer getTransfer() {
* return TextTransfer.getInstance();
* }
* public boolean isEnabled(DropTargetEvent event) {
* return true;
* }
* public void dragEnter(DropTargetEvent event) {}
* public void dragLeave(DropTargetEvent event) {}
* public void dragOperationChanged(DropTargetEvent event) {}
* public void dragOver(DropTargetEvent event) {}
* public void drop(DropTargetEvent event) {
* if (event.data == null)
* return;
* System.out.println(event.data);
* }
* public void dropAccept(DropTargetEvent event) {}
* });
* viewer.addDropSupport(DND.DROP_COPY | DND.DROP_MOVE, dropAdapter.getTransfers(), dropAdapter);
* </pre></code>
* @since 3.0
*/
public class DelegatingDropAdapter implements DropTargetListener {
private List<TransferDropTargetListener> listeners = new ArrayList<>();
private TransferDropTargetListener currentListener;
private int originalDropType;
/**
* Adds the given <code>TransferDropTargetListener</code>.
*
* @param listener the new listener
*/
public void addDropTargetListener(TransferDropTargetListener listener) {
listeners.add(listener);
}
/**
* The cursor has entered the drop target boundaries. The current listener is
* updated, and <code>#dragEnter()</code> is forwarded to the current listener.
*
* @param event the drop target event
* @see DropTargetListener#dragEnter(DropTargetEvent)
*/
@Override
public void dragEnter(DropTargetEvent event) {
// if (Policy.DEBUG_DRAG_DROP)
// System.out.println("Drag Enter: " + toString()); //$NON-NLS-1$
originalDropType = event.detail;
updateCurrentListener(event);
}
/**
* The cursor has left the drop target boundaries. The event is forwarded to the
* current listener.
*
* @param event the drop target event
* @see DropTargetListener#dragLeave(DropTargetEvent)
*/
@Override
public void dragLeave(final DropTargetEvent event) {
// if (Policy.DEBUG_DRAG_DROP)
// System.out.println("Drag Leave: " + toString()); //$NON-NLS-1$
setCurrentListener(null, event);
}
/**
* The operation being performed has changed (usually due to the user changing
* a drag modifier key while dragging). Updates the current listener and forwards
* this event to that listener.
*
* @param event the drop target event
* @see DropTargetListener#dragOperationChanged(DropTargetEvent)
*/
@Override
public void dragOperationChanged(final DropTargetEvent event) {
// if (Policy.DEBUG_DRAG_DROP)
// System.out.println("Drag Operation Changed to: " + event.detail); //$NON-NLS-1$
originalDropType = event.detail;
TransferDropTargetListener oldListener = getCurrentListener();
updateCurrentListener(event);
final TransferDropTargetListener newListener = getCurrentListener();
// only notify the current listener if it hasn't changed based on the
// operation change. otherwise the new listener would get a dragEnter
// followed by a dragOperationChanged with the exact same event.
if (newListener != null && newListener == oldListener) {
SafeRunnable.run(new SafeRunnable() {
@Override
public void run() throws Exception {
newListener.dragOperationChanged(event);
}
});
}
}
/**
* The cursor is moving over the drop target. Updates the current listener and
* forwards this event to that listener. If no listener can handle the drag
* operation the <code>event.detail</code> field is set to <code>DND.DROP_NONE</code>
* to indicate an invalid drop.
*
* @param event the drop target event
* @see DropTargetListener#dragOver(DropTargetEvent)
*/
@Override
public void dragOver(final DropTargetEvent event) {
TransferDropTargetListener oldListener = getCurrentListener();
updateCurrentListener(event);
final TransferDropTargetListener newListener = getCurrentListener();
// only notify the current listener if it hasn't changed based on the
// drag over. otherwise the new listener would get a dragEnter
// followed by a dragOver with the exact same event.
if (newListener != null && newListener == oldListener) {
SafeRunnable.run(new SafeRunnable() {
@Override
public void run() throws Exception {
newListener.dragOver(event);
}
});
}
}
/**
* Forwards this event to the current listener, if there is one. Sets the
* current listener to <code>null</code> afterwards.
*
* @param event the drop target event
* @see DropTargetListener#drop(DropTargetEvent)
*/
@Override
public void drop(final DropTargetEvent event) {
// if (Policy.DEBUG_DRAG_DROP)
// System.out.println("Drop: " + toString()); //$NON-NLS-1$
updateCurrentListener(event);
if (getCurrentListener() != null) {
SafeRunnable.run(new SafeRunnable() {
@Override
public void run() throws Exception {
getCurrentListener().drop(event);
}
});
}
setCurrentListener(null, event);
}
/**
* Forwards this event to the current listener if there is one.
*
* @param event the drop target event
* @see DropTargetListener#dropAccept(DropTargetEvent)
*/
@Override
public void dropAccept(final DropTargetEvent event) {
// if (Policy.DEBUG_DRAG_DROP)
// System.out.println("Drop Accept: " + toString()); //$NON-NLS-1$
if (getCurrentListener() != null) {
SafeRunnable.run(new SafeRunnable() {
@Override
public void run() throws Exception {
getCurrentListener().dropAccept(event);
}
});
}
}
/**
* Returns the listener which currently handles drop events.
*
* @return the <code>TransferDropTargetListener</code> which currently
* handles drop events.
*/
private TransferDropTargetListener getCurrentListener() {
return currentListener;
}
/**
* Returns the transfer data type supported by the given listener.
* Returns <code>null</code> if the listener does not support any of the
* specified data types.
*
* @param dataTypes available data types
* @param listener <code>TransferDropTargetListener</code> to use for testing
* supported data types.
* @return the transfer data type supported by the given listener or
* <code>null</code>.
*/
private TransferData getSupportedTransferType(TransferData[] dataTypes,
TransferDropTargetListener listener) {
for (TransferData dataType : dataTypes) {
if (listener.getTransfer().isSupportedType(dataType)) {
return dataType;
}
}
return null;
}
/**
* Returns the combined set of <code>Transfer</code> types of all
* <code>TransferDropTargetListeners</code>.
*
* @return the combined set of <code>Transfer</code> types
*/
public Transfer[] getTransfers() {
Transfer[] types = new Transfer[listeners.size()];
for (int i = 0; i < listeners.size(); i++) {
TransferDropTargetListener listener = listeners
.get(i);
types[i] = listener.getTransfer();
}
return types;
}
/**
* Returns <code>true</code> if there are no listeners to delegate events to.
*
* @return <code>true</code> if there are no <code>TransferDropTargetListeners</code>
* <code>false</code> otherwise
*/
public boolean isEmpty() {
return listeners.isEmpty();
}
/**
* Removes the given <code>TransferDropTargetListener</code>.
* Listeners should not be removed while a drag and drop operation is in progress.
*
* @param listener the listener to remove
*/
public void removeDropTargetListener(TransferDropTargetListener listener) {
if (currentListener == listener) {
currentListener = null;
}
listeners.remove(listener);
}
/**
* Sets the current listener to <code>listener</code>. Sends the given
* <code>DropTargetEvent</code> if the current listener changes.
*
* @return <code>true</code> if the new listener is different than the previous
* <code>false</code> otherwise
*/
private boolean setCurrentListener(TransferDropTargetListener listener,
final DropTargetEvent event) {
if (currentListener == listener) {
return false;
}
if (currentListener != null) {
SafeRunnable.run(new SafeRunnable() {
@Override
public void run() throws Exception {
currentListener.dragLeave(event);
}
});
}
currentListener = listener;
// if (Policy.DEBUG_DRAG_DROP)
// System.out.println("Current drop listener: " + listener); //$NON-NLS-1$
if (currentListener != null) {
SafeRunnable.run(new SafeRunnable() {
@Override
public void run() throws Exception {
currentListener.dragEnter(event);
}
});
}
return true;
}
/**
* Updates the current listener to one that can handle the drop. There can be many
* listeners and each listener may be able to handle many <code>TransferData</code>
* types. The first listener found that can handle a drop of one of the given
* <code>TransferData</code> types will be selected.
* If no listener can handle the drag operation the <code>event.detail</code> field
* is set to <code>DND.DROP_NONE</code> to indicate an invalid drop.
*
* @param event the drop target event
*/
private void updateCurrentListener(DropTargetEvent event) {
int originalDetail = event.detail;
// revert the detail to the "original" drop type that the User indicated.
// this is necessary because the previous listener may have changed the detail
// to something other than what the user indicated.
event.detail = originalDropType;
Iterator<TransferDropTargetListener> iter = listeners.iterator();
while (iter.hasNext()) {
TransferDropTargetListener listener = iter
.next();
TransferData dataType = getSupportedTransferType(event.dataTypes,
listener);
if (dataType != null) {
TransferData originalDataType = event.currentDataType;
// set the data type supported by the drop listener
event.currentDataType = dataType;
if (listener.isEnabled(event)) {
// if the listener stays the same, set its previously determined
// event detail
if (!setCurrentListener(listener, event)) {
event.detail = originalDetail;
}
return;
}
event.currentDataType = originalDataType;
}
}
setCurrentListener(null, event);
event.detail = DND.DROP_NONE;
// -always- ensure that expand/scroll are on...otherwise
// if a valid drop target is a child of an invalid one
// you can't get there...
event.feedback = DND.FEEDBACK_EXPAND | DND.FEEDBACK_SCROLL;
}
}