How to Write a Mouse-Motion Listener

How to Write a Mouse-Motion Listener

Mouse-motion events tell you when the user uses the mouse (or a similar input device) to move the onscreen cursor. For information on listening for other kinds of mouse events, such as clicks, see How to Write a Mouse Listener (page 689). For information on listening for mouse wheel events, see How to Write a Mouse Wheel Listener (page 699). If your program needs to detect both mouse events and mouse-motion events, you can use Swing's convenient MouseInputAdapter class, which implements both MouseListener and Mouse-MotionListener.

Figure shows an example with a mouse-motion listener. It's exactly like the example in How to Write a Mouse Listener (page 689), except for substituting MouseMotionListener^[28] for MouseListener, implementing the mouseDragged and mouseMoved methods instead of the mouse listener methods, and displaying coordinates instead of numbers of clicks.

^[28] MouseMotionListener API documentation: http://java.sun.com/j2se/1.4.2/docs/api/java/awt/event/MouseMotionListener.html.

Try This:

Here's the code from MouseMotionEventDemo.java that implements the mouse-motion event handling:

public class MouseMotionEventDemo extends JPanel

                                  implements MouseMotionListener {

    //...in initialization code:

        //Register for mouse events on blankArea and panel.

        blankArea.addMouseMotionListener(this);

        addMouseMotionListener(this);

        ...

    }

    public void mouseMoved(MouseEvent e) {

       saySomething("Mouse moved", e);

    }

    public void mouseDragged(MouseEvent e) {

       saySomething("Mouse dragged", e);

    }

    void saySomething(String eventDescription, MouseEvent e) {

        textArea.append(eventDescription

                        + " (" + e.getX() + "," + e.getY() + ")"

                        + " detected on "

                        + e.getComponent().getClass().getName()

                        + newline);

    }

}

A more interesting example is SelectionDemo, which is discussed in Introduction to Painting Concepts (page 134) in Chapter 6. The program draws a rectangle illustrating the user's current dragging. To do this, it must implement an event handler for three kinds of mouse events: mouse presses, mouse drags, and mouse releases. To be informed of all these events, the handler must implement both the MouseListener and MouseMotionListener interfaces, and be registered as both a mouse listener and a mouse-motion listener. To avoid having to define empty methods, the handler doesn't implement either listener interface directly. Instead, it extends MouseInputAdapter, as the following code snippet shows.

...//where initialization occurs:

    MyListener myListener = new MyListener();

    addMouseListener(myListener);

    addMouseMotionListener(myListener);

...

private class MyListener extends MouseInputAdapter {

    public void mousePressed(MouseEvent e) {

        int x = e.getX();

        int y = e.getY();

        currentRect = new Rectangle(x, y, 0, 0);

        updateDrawableRect(getWidth(), getHeight());

        repaint();

    }



    public void mouseDragged(MouseEvent e) {

        updateSize(e);

    }



    public void mouseReleased(MouseEvent e) {

        updateSize(e);

    }

    ...



    void updateSize(MouseEvent e) {

        int x = e.getX();

        int y = e.getY();

        ...

        repaint(...);

    }

The Mouse-Motion Listener API

Figure lists the methods in the MouseMotionListener. Each mouse-motion event method has a single parameter—and it's not called MouseMotionEvent. Instead, each mouse-motion event method uses a MouseEvent argument. You can find methods defined by the Mouse-Event class and its superclass InputEvent in Figure (page 692) and Figure (page 693), respectively. Also refer to the relevant API documentation at:

http://java.sun.com/j2se/1.4.2/docs/api/java/awt/event/MouseMotionListener.html

http://java.sun.com/j2se/1.4.2/docs/api/java/awt/event/MouseEvent.html

http://java.sun.com/j2se/1.4.2/docs/api/java/awt/event/InputEvent.html

^[a] MouseMotionAdapter API documentation: http://java.sun.com/j2se/1.4.2/docs/api/java/awt/event/MouseMotionAdapter.html.

Examples That Use Mouse-Motion Listeners

The following examples use mouse-motion listeners.

LayeredPaneDemo and LayeredPaneDemo2