moveinteractor.java

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package ui;

import javax.swing.event.MouseInputAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JComponent;

/**
 * MoveInteractor is a generic interactor for dragging components around
 * inside a container.  It can listen to any number of components for
 * click-and-drag events, but only one component can be actively dragged
 * at any moment.  (This is not a serious limitation, since most user 
 * interfaces only support one mouse.)  It can handle any number of containers,
 * but a component can't be dragged outside of its container.
 * <p>
 * If a container has a layout manager, the behavior of MoveInteractor is
 * not well defined, since it will fight with the layout manager to position
 * the dragged component.
 */
public class MoveInteractor extends MouseInputAdapter {

    /**
     * Make a MoveInteractor.
     */
    public MoveInteractor() {
    }
    
    /**
     * Attach this move interactor to a component that can be
     * dragged around.
     * @param comp Draggable component
     * @modifies comp's listeners
     * @effects When the user clicks and drags comp, this
     * MoveInteractor moves comp around with the mouse. 
     */
    public void listenTo(JComponent comp) {
        comp.addMouseListener(this);
        comp.addMouseMotionListener(this);
    }
    
    /**
     * Test whether a component may be picked up and dragged.
     * Called when the user presses the mouse button over a component
     * that this interactor is listening to. 
     * Subclasses should override this method if components
     * are sometimes undraggable.  (For example, in a game,
     * the user may move only their own pieces, only during their turn.)
     * The default implementation of this method simply returns true. 
     * 
     * @param comp component that user clicked on
     * @param x x coordinate of mouse pointer, <b>relative to comp</b>
     * @param y y coordinate of mouse pointer, <b>relative to comp</b>
     * @return true if component may be dragged, false if drag should be
     * stopped
     */
    public boolean pickUp(JComponent comp, int x, int y) {
        return true;
    }
    
    /**
     * Finish a drag operation by dropping the component.
     * Called when the user releases the mouse button.
     * Subclasses should override this method if there are some
     * locations that a component can't be dropped (like
     * illegal moves in a game), or if the drop should have some 
     * other effect (like changing a backend model).
     * The default implementation of this method simply returns true.
     *  
     * @param comp component being dragged
     * @param x x coordinate of mouse pointer, <b>relative to comp</b>
     * @param y y coordinate of mouse pointer, <b>relative to comp</b>
     * 
     * @effects May reposition comp, e.g. snapping it to the correct location.
     * May also trigger effects in other classes.
     * 
     * @return true if the drop is permitted, in which
     * case MoveInteractor leaves the component where it is;
     * false if the drop should be canceled, in which case MoveInteractor
     * restores the component to its original location 
     */
    public boolean drop(JComponent comp, int x, int y) {
        return true;
    }
    
    /**
     * Part of MouseListener interface.  Called when user presses
     * the mouse button over a component that this MoveInteractor is
     * listening to. 
     */
    public void mousePressed(MouseEvent e) {
        // YOUR CODE HERE
    }
    
    /**
     * Part of MouseMotionListener interface.  Called when user is
     * dragging the mouse.
     */
    public void mouseDragged(MouseEvent e) {
        // YOUR CODE HERE
    }
    
    /**
     * Part of MouseListener interface.  Called when user releases
     * the mouse button.
     */
    public void mouseReleased(MouseEvent e) {
        // YOUR CODE HERE
    }
}