org.eclipse.jface.util.DelegatingDropAdapter Maven / Gradle / Ivy
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/*******************************************************************************
* Copyright (c) 2000, 2015 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
*******************************************************************************/
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 DelegatingDropAdapter is a DropTargetListener
* that maintains and delegates to a set of {@link TransferDropTargetListener}s.
* Each TransferDropTargetListener can then be implemented as if it
* were the DropTarget's only DropTargetListener.
*
* On dragEnter, dragOperationChanged,
* dragOver and drop, a current listener is
* obtained from the set of all TransferDropTargetListeners. The
* current listener is the first listener to return true for
* {@link TransferDropTargetListener#isEnabled(DropTargetEvent)}. The current
* listener is forwarded all DropTargetEvents until some other
* listener becomes the current listener, or the drop terminates.
*
*
* After adding all TransferDropTargetListeners to the
* DelegatingDropAdapter the combined set of Transfers
* should be set in the SWT DropTarget.
* #getTransfers() provides the set of Transfer types
* of all TransferDropTargetListeners.
*
*
* The following example snippet shows a DelegatingDropAdapter with
* two TransferDropTargetListeners. One supports dropping resources
* and demonstrates how a listener can be disabled in the isEnabled method. The
* other listener supports text transfer.
*
*
*
*
* 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);
*
*
*
* @since 3.0
*/
public class DelegatingDropAdapter implements DropTargetListener {
private List listeners = new ArrayList<>();
private TransferDropTargetListener currentListener;
private int originalDropType;
/**
* Adds the given TransferDropTargetListener.
*
* @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 #dragEnter() 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 event.detail field is set to DND.DROP_NONE
* 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 null 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 TransferDropTargetListener which currently
* handles drop events.
*/
private TransferDropTargetListener getCurrentListener() {
return currentListener;
}
/**
* Returns the transfer data type supported by the given listener.
* Returns null if the listener does not support any of the
* specified data types.
*
* @param dataTypes available data types
* @param listener TransferDropTargetListener to use for testing
* supported data types.
* @return the transfer data type supported by the given listener or
* null.
*/
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 Transfer types of all
* TransferDropTargetListeners.
*
* @return the combined set of Transfer 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 true if there are no listeners to delegate events to.
*
* @return true if there are no TransferDropTargetListeners
* false otherwise
*/
public boolean isEmpty() {
return listeners.isEmpty();
}
/**
* Removes the given TransferDropTargetListener.
* 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 listener. Sends the given
* DropTargetEvent if the current listener changes.
*
* @return true if the new listener is different than the previous
* false 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 TransferData
* types. The first listener found that can handle a drop of one of the given
* TransferData types will be selected.
* If no listener can handle the drag operation the event.detail field
* is set to DND.DROP_NONE 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 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;
}
}