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| java.lang.Object
 java.awt.MediaTracker
| MediaTracker | | public class MediaTracker implements java.io.Serializable(Code) | | The MediaTracker class is a utility class to track
the status of a number of media objects. Media objects could
include audio clips as well as images, though currently only
images are supported.
To use a media tracker, create an instance of
MediaTracker and call its addImage
method for each image to be tracked. In addition, each image can
be assigned a unique identifier. This identifier controls the
priority order in which the images are fetched. It can also be used
to identify unique subsets of the images that can be waited on
independently. Images with a lower ID are loaded in preference to
those with a higher ID number.
Tracking an animated image
might not always be useful
due to the multi-part nature of animated image
loading and painting,
but it is supported.
MediaTracker treats an animated image
as completely loaded
when the first frame is completely loaded.
At that point, the MediaTracker
signals any waiters
that the image is completely loaded.
If no ImageObservers are observing the image
when the first frame has finished loading,
the image might flush itself
to conserve resources
(see
Image.flush ).
Here is an example of using MediaTracker:
import java.applet.Applet;
import java.awt.Color;
import java.awt.Image;
import java.awt.Graphics;
import java.awt.MediaTracker;
public class ImageBlaster extends Applet implements Runnable {
MediaTracker tracker;
Image bg;
Image anim[] = new Image[5];
int index;
Thread animator;
// Get the images for the background (id == 0)
// and the animation frames (id == 1)
// and add them to the MediaTracker
public void init() {
tracker = new MediaTracker(this);
bg = getImage(getDocumentBase(),
"images/background.gif");
tracker.addImage(bg, 0);
for (int i = 0; i < 5; i++) {
anim[i] = getImage(getDocumentBase(),
"images/anim"+i+".gif");
tracker.addImage(anim[i], 1);
}
}
// Start the animation thread.
public void start() {
animator = new Thread(this);
animator.start();
}
// Stop the animation thread.
public void stop() {
animator = null;
}
// Run the animation thread.
// First wait for the background image to fully load
// and paint. Then wait for all of the animation
// frames to finish loading. Finally, loop and
// increment the animation frame index.
public void run() {
try {
tracker.waitForID(0);
tracker.waitForID(1);
} catch (InterruptedException e) {
return;
}
Thread me = Thread.currentThread();
while (animator == me) {
try {
Thread.sleep(100);
} catch (InterruptedException e) {
break;
}
synchronized (this) {
index++;
if (index >= anim.length) {
index = 0;
}
}
repaint();
}
}
// The background image fills the frame so we
// don't need to clear the applet on repaints.
// Just call the paint method.
public void update(Graphics g) {
paint(g);
}
// Paint a large red rectangle if there are any errors
// loading the images. Otherwise always paint the
// background so that it appears incrementally as it
// is loading. Finally, only paint the current animation
// frame if all of the frames (id == 1) are done loading,
// so that we don't get partial animations.
public void paint(Graphics g) {
if ((tracker.statusAll(false) & MediaTracker.ERRORED) != 0) {
g.setColor(Color.red);
g.fillRect(0, 0, size().width, size().height);
return;
}
g.drawImage(bg, 0, 0, this);
if (tracker.statusID(1, false) == MediaTracker.COMPLETE) {
g.drawImage(anim[index], 10, 10, this);
}
}
}
version:
1.52, 06/05/07
author:
Jim Graham
since:
JDK1.0 |
| Field Summary | |
| final public static int | ABORTED
Flag indicating that the downloading of media was aborted. | | final public static int | COMPLETE
Flag indicating that the downloading of media was completed
successfully. | | final static int | DONE
| | final public static int | ERRORED
Flag indicating that the downloading of media encountered
an error. | | final public static int | LOADING
Flag indicating that media is currently being loaded. | | MediaEntry | head
The head of the list of Images that is being
tracked by the MediaTracker. | | Component | target
A given Component that will be
tracked by a media tracker where the image will
eventually be drawn. |
| Constructor Summary | |
| public | MediaTracker(Component comp)
Creates a media tracker to track images for a given component. |
| Method Summary | |
| public void | addImage(Image image, int id)
Adds an image to the list of images being tracked by this media
tracker. | | public synchronized void | addImage(Image image, int id, int w, int h)
Adds a scaled image to the list of images being tracked
by this media tracker. | | public boolean | checkAll()
Checks to see if all images being tracked by this media tracker
have finished loading. | | public boolean | checkAll(boolean load)
Checks to see if all images being tracked by this media tracker
have finished loading. | | public boolean | checkID(int id)
Checks to see if all images tracked by this media tracker that
are tagged with the specified identifier have finished loading. | | public boolean | checkID(int id, boolean load)
Checks to see if all images tracked by this media tracker that
are tagged with the specified identifier have finished loading. | | public synchronized Object[] | getErrorsAny()
Returns a list of all media that have encountered an error. | | public synchronized Object[] | getErrorsID(int id)
Returns a list of media with the specified ID that
have encountered an error. | | public synchronized boolean | isErrorAny()
Checks the error status of all of the images. | | public synchronized boolean | isErrorID(int id)
Checks the error status of all of the images tracked by this
media tracker with the specified identifier. | | public synchronized void | removeImage(Image image)
Removes the specified image from this media tracker. | | public synchronized void | removeImage(Image image, int id)
Removes the specified image from the specified tracking
ID of this media tracker. | | public synchronized void | removeImage(Image image, int id, int width, int height)
Removes the specified image with the specified
width, height, and ID from this media tracker. | | synchronized void | setDone()
| | public int | statusAll(boolean load)
Calculates and returns the bitwise inclusive OR of the
status of all media that are tracked by this media tracker. | | public int | statusID(int id, boolean load)
Calculates and returns the bitwise inclusive OR of the
status of all media with the specified identifier that are
tracked by this media tracker. | | public void | waitForAll()
Starts loading all images tracked by this media tracker. | | public synchronized boolean | waitForAll(long ms)
Starts loading all images tracked by this media tracker. | | public void | waitForID(int id)
Starts loading all images tracked by this media tracker with the
specified identifier. | | public synchronized boolean | waitForID(int id, long ms)
Starts loading all images tracked by this media tracker with the
specified identifier. |
| DONE | | final static int DONE(Code) | | |
| MediaTracker | | public MediaTracker(Component comp)(Code) | | Creates a media tracker to track images for a given component.
Parameters:
comp - the component on which the images will eventually be drawn |
| addImage | | public void addImage(Image image, int id)(Code) | | Adds an image to the list of images being tracked by this media
tracker. The image will eventually be rendered at its default
(unscaled) size.
Parameters:
image - the image to be tracked
Parameters:
id - an identifier used to track this image |
| addImage | | public synchronized void addImage(Image image, int id, int w, int h)(Code) | | Adds a scaled image to the list of images being tracked
by this media tracker. The image will eventually be
rendered at the indicated width and height.
Parameters:
image - the image to be tracked
Parameters:
id - an identifier that can be used to track this image
Parameters:
w - the width at which the image is rendered
Parameters:
h - the height at which the image is rendered |
| checkAll | | public boolean checkAll(boolean load)(Code) | | Checks to see if all images being tracked by this media tracker
have finished loading.
If the value of the load flag is true,
then this method starts loading any images that are not yet
being loaded.
If there is an error while loading or scaling an image, that
image is considered to have finished loading. Use the
isErrorAny and isErrorID methods to
check for errors.
Parameters:
load - if true, start loading any images that are not yet being loaded true if all images have finished loading, have been aborted, or have encountered an error; false otherwise
See Also: java.awt.MediaTracker.checkID
See Also: java.awt.MediaTracker.checkAll
See Also: java.awt.MediaTracker.isErrorAny
See Also: java.awt.MediaTracker.isErrorID(int) |
| checkID | | public boolean checkID(int id)(Code) | | Checks to see if all images tracked by this media tracker that
are tagged with the specified identifier have finished loading.
This method does not start loading the images if they are not
already loading.
If there is an error while loading or scaling an image, then that
image is considered to have finished loading. Use the
isErrorAny or isErrorID methods to
check for errors.
Parameters:
id - the identifier of the images to check true if all images have finished loading, have been aborted, or have encountered an error; false otherwise
See Also: java.awt.MediaTracker.checkID(intboolean)
See Also: java.awt.MediaTracker.checkAll
See Also: java.awt.MediaTracker.isErrorAny
See Also: java.awt.MediaTracker.isErrorID(int) |
| checkID | | public boolean checkID(int id, boolean load)(Code) | | Checks to see if all images tracked by this media tracker that
are tagged with the specified identifier have finished loading.
If the value of the load flag is true,
then this method starts loading any images that are not yet
being loaded.
If there is an error while loading or scaling an image, then that
image is considered to have finished loading. Use the
isErrorAny or isErrorID methods to
check for errors.
Parameters:
id - the identifier of the images to check
Parameters:
load - if true, start loading any images that are not yet being loaded true if all images have finished loading, have been aborted, or have encountered an error; false otherwise
See Also: java.awt.MediaTracker.checkID(intboolean)
See Also: java.awt.MediaTracker.checkAll
See Also: java.awt.MediaTracker.isErrorAny
See Also: java.awt.MediaTracker.isErrorID(int) |
| isErrorID | | public synchronized boolean isErrorID(int id)(Code) | | Checks the error status of all of the images tracked by this
media tracker with the specified identifier.
Parameters:
id - the identifier of the images to check true if any of the images with the specified identifier had an error during loading; false otherwise
See Also: java.awt.MediaTracker.isErrorAny
See Also: java.awt.MediaTracker.getErrorsID |
| removeImage | | public synchronized void removeImage(Image image, int id, int width, int height)(Code) | | Removes the specified image with the specified
width, height, and ID from this media tracker.
Only the specified instance (with any duplicates) is removed.
Parameters:
image - the image to be removed
Parameters:
id - the tracking ID from which to remove the image
Parameters:
width - the width to remove (-1 for unscaled)
Parameters:
height - the height to remove (-1 for unscaled)
See Also: java.awt.MediaTracker.removeImage(java.awt.Image)
See Also: java.awt.MediaTracker.removeImage(java.awt.Imageint)
since:
JDK1.1 |
| setDone | | synchronized void setDone()(Code) | | |
| statusID | | public int statusID(int id, boolean load)(Code) | | Calculates and returns the bitwise inclusive OR of the
status of all media with the specified identifier that are
tracked by this media tracker.
Possible flags defined by the
MediaTracker class are LOADING,
ABORTED, ERRORED, and
COMPLETE. An image that hasn't started
loading has zero as its status.
If the value of load is true, then
this method starts loading any images that are not yet being loaded.
Parameters:
id - the identifier of the images to check
Parameters:
load - if true, start loading any images that are not yet being loaded the bitwise inclusive OR of the status of all of the media with the specifiedidentifier that are being tracked
See Also: java.awt.MediaTracker.statusAll(boolean)
See Also: java.awt.MediaTracker.LOADING
See Also: java.awt.MediaTracker.ABORTED
See Also: java.awt.MediaTracker.ERRORED
See Also: java.awt.MediaTracker.COMPLETE |
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