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java.lang.Object | +----java.awt.MediaTracker
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.
Here is an example:
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.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);
}
}
}
ABORTED
COMPLETE
ERRORED
LOADING
MediaTracker(Component)
addImage(Image, int)
addImage(Image, int, int, int)
checkAll()
checkAll(boolean)
checkID(int)
checkID(int, boolean)
getErrorsAny()
getErrorsID(int)
isErrorAny()
isErrorID(int)
removeImage(Image)
removeImage(Image, int)
removeImage(Image, int, int, int)
statusAll(boolean)
statusID(int, boolean)
waitForAll()
waitForAll(long)
waitForID(int)
waitForID(int, long)
LOADING
public static final int LOADING
ABORTED
public static final int ABORTED
ERRORED
public static final int ERRORED
COMPLETE
public static final int COMPLETE
MediaTracker
public MediaTracker(Component comp)
addImage
public void addImage(Image image,
int id)
addImage
public synchronized void addImage(Image image,
int id,
int w,
int h)
checkAll
public boolean checkAll()
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.
true if all images have finished loading,
have been aborted, or have encountered
an error; false otherwise.
checkAll
public boolean checkAll(boolean load)
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.
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.
isErrorAny
public synchronized boolean isErrorAny()
true if any of the images tracked
by this media tracker had an error during
loading; false otherwise.
getErrorsAny
public synchronized Object[] getErrorsAny()
null if
there are none with errors.
waitForAll
public void waitForAll() throws InterruptedException
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.
waitForAll
public synchronized boolean waitForAll(long ms) throws InterruptedException
ms argument has passed.
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.
true if all images were successfully
loaded; false otherwise.
statusAll
public int statusAll(boolean load)
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.
true, start loading
any images that are not yet being loaded.
checkID
public boolean checkID(int id)
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.
true if all images have finished loading,
have been aborted, or have encountered
an error; false otherwise.
checkID
public boolean checkID(int id,
boolean load)
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.
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.
isErrorID
public synchronized boolean isErrorID(int id)
true if any of the images with the
specified identifier had an error during
loading; false otherwise.
getErrorsID
public synchronized Object[] getErrorsID(int id)
null if there are none with errors.
waitForID
public void waitForID(int id) throws InterruptedException
If there is an error while loading or scaling an image, then that
image is considered to have finished loading. Use the
isErrorAny and isErrorID methods to
check for errors.
waitForID
public synchronized boolean waitForID(int id,
long ms) throws InterruptedException
ms
argument has passed.
If there is an error while loading or scaling an image, then that
image is considered to have finished loading. Use the
statusID, isErrorID, and
isErrorAny methods to check for errors.
statusID
public int statusID(int id,
boolean load)
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.
true, start loading
any images that are not yet being loaded.
removeImage
public synchronized void removeImage(Image image)
removeImage
public synchronized void removeImage(Image image,
int id)
Image being tracked
under the specified ID are removed regardless of scale.
removeImage
public synchronized void removeImage(Image image,
int id,
int width,
int height)
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