source: josm/src/org/openstreetmap/josm/actions/mapmode/MoveAction.java@ 104

package org.openstreetmap.josm.actions.mapmode;

import static org.openstreetmap.josm.tools.I18n.tr;

import java.awt.Cursor;
import java.awt.Point;
import java.awt.event.KeyEvent;
import java.awt.event.MouseEvent;
import java.util.Collection;

import javax.swing.JOptionPane;

import org.openstreetmap.josm.Main;
import org.openstreetmap.josm.command.Command;
import org.openstreetmap.josm.command.MoveCommand;
import org.openstreetmap.josm.data.coor.EastNorth;
import org.openstreetmap.josm.data.osm.Node;
import org.openstreetmap.josm.data.osm.OsmPrimitive;
import org.openstreetmap.josm.data.osm.visitor.AllNodesVisitor;
import org.openstreetmap.josm.gui.MapFrame;
import org.openstreetmap.josm.tools.ImageProvider;
/**
 * Move is an action that can move all kind of OsmPrimitives (except Keys for now).
 * 
 * If any object is selected, all selected objects are moved. If no object is 
 * selected, the nearest object will be selected and moved. In this case, the
 * object will be unselected as soon as movement stopped.
 * 
 * @author imi
 */
public class MoveAction extends MapMode {
        /**
         * The old cursor before the user pressed the mouse button.
         */
        private Cursor oldCursor;
        /**
         * The position of the mouse before the user moves a node.
         */
        private Point mousePos;
        /**
         * Non-<code>null</code>, if no object was selected before movement 
         * (and so the object get unselected after mouse release).
         */
        private OsmPrimitive singleOsmPrimitive;

        /**
         * Create a new MoveAction
         * @param mapFrame The MapFrame, this action belongs to.
         */
        public MoveAction(MapFrame mapFrame) {
                super(tr("Move"), 
                                "move", 
                                tr("Move selected objects around."), 
                                "M", 
                                KeyEvent.VK_M, 
                                mapFrame, 
                                ImageProvider.getCursor("normal", "move"));
        }

        @Override public void enterMode() {
                super.enterMode();
                Main.map.mapView.addMouseListener(this);
                Main.map.mapView.addMouseMotionListener(this);
        }

        @Override public void exitMode() {
                super.exitMode();
                Main.map.mapView.removeMouseListener(this);
                Main.map.mapView.removeMouseMotionListener(this);
        }

        
        /**
         * If the left mouse button is pressed, move all currently selected
         * objects.
         */
        @Override public void mouseDragged(MouseEvent e) {
                if ((e.getModifiersEx() & MouseEvent.BUTTON1_DOWN_MASK) == 0)
                        return;
                
                if (mousePos == null) {
                        mousePos = e.getPoint();
                        singleOsmPrimitive = null;
                }

                EastNorth mouseGeo = Main.map.mapView.getEastNorth(e.getX(), e.getY());
                EastNorth mouseStartGeo = Main.map.mapView.getEastNorth(mousePos.x, mousePos.y);
                double dx = mouseGeo.east() - mouseStartGeo.east();
                double dy = mouseGeo.north() - mouseStartGeo.north();
                if (dx == 0 && dy == 0)
                        return;

                Collection<OsmPrimitive> selection = Main.ds.getSelected();
                Collection<Node> affectedNodes = AllNodesVisitor.getAllNodes(selection);
                
                // check if any coordinate would be outside the world
                for (OsmPrimitive osm : affectedNodes) {
                        if (osm instanceof Node && ((Node)osm).coor.isOutSideWorld()) {
                                JOptionPane.showMessageDialog(Main.parent,tr("Cannot move objects outside of the world."));
                                return;
                        }
                }
                
                Command c = !Main.main.editLayer().commands.isEmpty() ? Main.main.editLayer().commands.getLast() : null;
                if (c instanceof MoveCommand && affectedNodes.equals(((MoveCommand)c).objects))
                        ((MoveCommand)c).moveAgain(dx,dy);
                else
                        Main.main.editLayer().add(new MoveCommand(selection, dx, dy));
                
                Main.map.mapView.repaint();
                mousePos = e.getPoint();
        }

        /**
         * Look, whether any object is selected. If not, select the nearest node.
         * If there are no nodes in the dataset, do nothing.
         * 
         * If the user did not press the left mouse button, do nothing.
         * 
         * Also remember the starting position of the movement and change the mouse 
         * cursor to movement.
         */
        @Override public void mousePressed(MouseEvent e) {
                if (e.getButton() != MouseEvent.BUTTON1)
                        return;

                if (Main.ds.getSelected().size() == 0) {
                        OsmPrimitive osm = Main.map.mapView.getNearest(e.getPoint(), (e.getModifiersEx() & MouseEvent.ALT_DOWN_MASK) != 0);
                        if (osm != null)
                                Main.ds.setSelected(osm);
                        singleOsmPrimitive = osm;
                        Main.map.mapView.repaint();
                } else
                        singleOsmPrimitive = null;
                
                mousePos = e.getPoint();
                oldCursor = Main.map.mapView.getCursor();
                Main.map.mapView.setCursor(Cursor.getPredefinedCursor(Cursor.MOVE_CURSOR));
        }
        
        /**
         * Restore the old mouse cursor.
         */
        @Override public void mouseReleased(MouseEvent e) {
                Main.map.mapView.setCursor(oldCursor);
                if (singleOsmPrimitive != null) {
                        Main.ds.clearSelection();
                        Main.map.mapView.repaint();
                }
        }
}