如何编写鼠标运动监听器

Mouse-motion events notify 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. For information on listening for mouse-wheel events, see How to Write a Mouse Wheel Listener.

If an application requires the detection of both mouse events and mouse-motion events, use the MouseInputAdapter class, which implements the MouseInputListener a convenient interface that implements both the MouseListener and MouseMotionListener interfaces.

Alternatively, use the corresponding MouseAdapter AWT class, which implements the MouseMotionListener interface, to create a MouseMotionEvent and override the methods for the specific events.

The following demo code contains a mouse-motion listener. This demo is exactly the same as the demo described in the How to Write a Mouse Listener section, except for substituting the MouseMotionListener interface for the MouseListener interface. Additionally, MouseMotionEventDemo implements the mouseDragged and mouseMoved methods instead of the mouse listener methods, and displays coordinates instead of numbers of clicks.

You can find the demo's code in MouseMotionEventDemo.java and BlankArea.java. The following code snippet from MouseMotionEventDemo 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);
    }
}

The SelectionDemo example, draws a rectangle illustrating the user's current dragging. To draw the rectangle, the application 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();
        currentRect.setSize(x - currentRect.x,
                            y - currentRect.y);
        updateDrawableRect(getWidth(), getHeight());
        Rectangle totalRepaint = rectToDraw.union(previouseRectDrawn); 
        repaint(totalRepaint.x, totalRepaint.y,
                totalRepaint.width, totalRepaint.height);
    }
}

The Mouse-Motion Listener API

The MouseMotionListener Interface

The corresponding adapter classes are MouseMotionAdapter and MouseAdapter.

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. See The MouseEvent API for information about using MouseEvent objects.

Examples That Use Mouse-Motion Listeners

The following table lists the examples that use mouse-motion listeners.