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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. If your program needs to detect both mouse events and mouse-motion events, you can use Swing's convenientMouseInputAdapter
class, which implements bothMouseListener
andMouseMotionListener
.The following applet contains a mouse-motion listener. It's exactly like the applet in How to Write a Mouse Listener, except for substituting
MouseMotionListener
forMouseListener
, implementing themouseDragged
andmouseMoved
methods instead of the mouse listener methods, and displaying coordinates instead of numbers of clicks. You can find the applet's code inMouseMotionEventDemo.java
and
BlankArea.java
.
This is a picture of the applet's GUI. To run the applet, click the picture. The applet will appear in a new browser window.
Here is the code that implements the mouse-motion event handling:
Try this:
- Move the cursor into the yellow rectangle at the top of the applet.
You'll see one or more mouse-moved events.- Press and hold the mouse button, and then move the mouse so that the cursor is outside the yellow rectangle.
You'll see mouse-dragged events.public class MouseMotionEventDemo extends JApplet implements MouseMotionListener { //...in initialization code: //Register for mouse events on blankArea and applet (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 Arguments to the repaint Method. 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
andMouseMotionListener
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 extendsMouseInputAdapter
, as the following code snippet shows....//where initialization occurs: 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(...); } }
TheMouseMotionListener
interface and its corresponding adapter class,
MouseMotionAdapter
, contain these methods:
Each mouse-motion event method has a single parameter -- and it's not called
void mouseDragged(MouseEvent)
- 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.
void mouseMoved(MouseEvent)
- 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.
MouseMotionEvent
! Instead, each mouse-motion event method has aMouseEvent
argument. See The Mouse Event API for information about usingMouseEvent
objects.
The following table lists the examples that use mouse-motion listeners.
Example Where Described Notes MouseMotionEventDemo
This section Reports all mouse motion events that occur within a blank panel to demonstrate the circumstances under which mouse motion events are fired. LayeredPaneDemo
and
LayeredPaneDemo2
How to Use Layered Panes Moves an image of Duke around within a layered pane in response to mouse motion events. SelectionDemo
Getting Started An applet that lets the user drag a rectangle to select a portion of an image. Uses a subclass of MouseInputAdapter
to listen to both mouse events and mouse-motion events.GlassPaneDemo
How to Use Root Panes Uses a subclass of MouseInputAdapter
to listen to mouse events and mouse-motion events on the root pane's glass pane. Redispatches the events to underlying components.
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