mousemotionlistener.html

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            <div id=PageTitle>How to Write a Mouse-Motion Listener</div>
            <blockquote>

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 <a href="mouselistener.html">How to Write a Mouse Listener</a>.
For information on listening for mouse-wheel events,
see <a href="mousewheellistener.html">How to Write a Mouse
Wheel Listener</a>.
If your program needs to detect both mouse events
and mouse-motion events,
you can use Swing's convenient <code>MouseInputAdapter</code> class,
which implements both <code>MouseListener</code> and
<code>MouseMotionListener</code>.

<p>
The following demo contains a mouse-motion listener.
It's exactly like the example in 
<a href="mouselistener.html">How to Write a Mouse Listener</a>,
except for substituting <code>MouseMotionListener</code>
for <code>MouseListener</code>,
implementing the <code>mouseDragged</code> and
<code>mouseMoved</code> methods 
instead of the mouse listener methods,
and displaying coordinates instead of numbers of clicks.

<p>

<p><center><IMG SRC="../../figures/uiswing/events/MouseMotionEventDemo.png" WIDTH="413" HEIGHT="261" ALIGN="BOTTOM" ALT=""></center></p>

<p>
<blockquote><hr><strong>Try this:</strong>&nbsp;
<ol>
<li> <a href="http://java.sun.com/docs/books/tutorialJWS/uiswing/events/examples/MouseMotionEventDemo.jnlp">Run
     MouseMotionEventDemo</a> using
     <a href=http://java.sun.com/products/javawebstart>
     Java<sup><font size=-2>TM</font></sup> Web Start</a>.
     Or, to compile and run the example yourself,
     consult the
     <a href="examples/index.html#MouseMotionEventDemo">example index</a>.

<li> Move the cursor into the yellow rectangle
     at the top of the window.
     <br>
     You'll see one or more mouse-moved events.
<li> Press and hold the mouse button,
     and then move the mouse so that the cursor
     is outside the yellow rectangle.
     <br>
     You'll see mouse-dragged events.
</ol>
<hr></blockquote>


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

<blockquote><pre>
public class MouseMotionEventDemo extends JPanel 
                                  implements MouseMotionListener {
    <em>//...in initialization code:</em>
        //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);
    }
}
</pre></blockquote>

<p>
A more interesting example is <code>SelectionDemo</code>,
which is discussed in 
<a class="TutorialLink" target="_top" href="../painting/concepts2.html">Introduction to Painting Concepts</a>.
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
<code>MouseListener</code> and 
<code>MouseMotionListener</code> 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 <code>MouseInputAdapter</code>,
as the following code snippet shows.

<p>
<font color=red>[PENDING: When this example has been
updated, check the code.]</font>

<blockquote><pre>
<em>...//where initialization occurs:</em>
    MyListener myListener = new MyListener();
    addMouseListener(myListener);
    addMouseMotionListener(myListener);
...
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(...);
    }
}
</pre></blockquote>

</blockquote>
<h3>
<a name="api">The Mouse-Motion Listener API</a></h3>
<blockquote>

<p align=center><a name="mousemotionlistener">The MouseMotionListener
   Interface</a>
<p><em>The corresponding adapter class is
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/java/awt/event/MouseMotionAdapter.html"><code>MouseMotionAdapter</code></a>.</em>
<table border=1>
<tr>
<th align=left>Method</th>
<th align=left>Purpose</th>
</tr>

<tr>
<td>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/java/awt/event/MouseMotionListener.html#mouseDragged(java.awt.event.MouseEvent)">mouseDragged(MouseEvent)</a></td>
<td> Called in response to the user moving
     the mouse while holding a mouse button down.
     This event is fired by the component
     that fired the most recent mouse-pressed event,
     even if the cursor is no longer over that component.
</td>
</tr>

<tr>
<td>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/java/awt/event/MouseMotionListener.html#mouseMoved(java.awt.event.MouseEvent)">mouseMoved(MouseEvent)</a></td>
<td> Called in response to the user moving
     the mouse with no mouse buttons pressed.
     This event is fired by the component
     that's currently under the cursor.
</td>
</tr>
</table>

<p>
Each mouse-motion event method has a single parameter &#151;
and it's <em>not</em> called <code>MouseMotionEvent</code>!
Instead, each mouse-motion event method uses a
<code>MouseEvent</code> argument.
See <a href="mouselistener.html#mouseevent">The MouseEvent API</a>
for information about using <code>MouseEvent</code> objects.
</blockquote>

<a name="eg">
<h3>Examples that Use Mouse-Motion Listeners</h3>
</a>
<blockquote>
The following table lists the
examples that use mouse-motion listeners.

<p>

<table>
<tr>
<th align=left> Example
</th>
<th align=left> Where Described
</th>
<th align=left> Notes
 
</th>
</tr>

<tr valign=top>
<td> <a href="examples/index.html#MouseMotionEventDemo"><code>MouseMotionEventDemo</code></a>
</td>
<td> This section
</td>
<td> Reports all mouse motion events that occur within a blank panel
     to demonstrate the circumstances under which mouse motion events are fired.

</td>
</tr>

<tr valign=top>
<td> <a href="../components/examples/index.html#LayeredPaneDemo"><code>LayeredPaneDemo</code></a> and
     <br>
     <a href="../components/examples/index.html#LayeredPaneDemo2"><code>LayeredPaneDemo2</code></a>
</td>
<td>
<a class="TutorialLink" target="_top" href="../components/layeredpane.html">How to Use Layered Panes</a></td>
<td> Moves an image of Duke around within a layered pane
     in response to mouse motion events.

</td>
</tr>

<tr valign=top>
<td><a href="../painting/examples/index.html#SelectionDemo"><code>SelectionDemo</code></a>
</td>
<td>
<a class="TutorialLink" target="_top" href="../painting/concepts2.html">Introduction to Painting Concepts</a></td>
<td> Lets the user drag a rectangle to select a portion
     of an image. Uses a subclass of <code>MouseInputAdapter</code>
     to listen to both mouse events and mouse-motion events.

</td>
</tr>

<tr valign=top>
<td><a href="../components/examples/index.html#GlassPaneDemo"><code>GlassPaneDemo</code></a>
</td>
<td>
<a class="TutorialLink" target="_top" href="../components/rootpane.html">How to Use Root Panes</a></td>
<td> Uses a subclass of <code>MouseInputAdapter</code> to
     listen to mouse events and mouse-motion events
     on the root pane's glass pane.
     Redispatches the events to underlying components.
</td>
</tr>
 
<tr valign=top>
<td><a href="../components/examples/index.html#ScrollDemo"><code>ScrollDemo</code></a>
</td>
<td>
<a class="TutorialLink" target="_top" href="../components/scrollpane.html">How to Use Scroll Panes</a></td>
<td> The label subclass, ScrollablePicture, uses a mouse-motion
     listener to allow the user to scroll the picture even when
     the user drags outside the window.
</td>
</tr>
</table>



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