public class MediaTracker extends Object implements Serializable
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);
}
}
}
| Modifier and Type | Field and Description |
|---|---|
static int |
ABORTED
Flag indicating that the downloading of media was aborted.
|
static int |
COMPLETE
Flag indicating that the downloading of media was completed
successfully.
|
(package private) static int |
DONE |
static int |
ERRORED
Flag indicating that the downloading of media encountered
an error.
|
(package private) MediaEntry |
head
The head of the list of
Images that is being
tracked by the MediaTracker. |
static int |
LOADING
Flag indicating that media is currently being loaded.
|
(package private) Component |
target
A given
Component that will be
tracked by a media tracker where the image will
eventually be drawn. |
| Constructor and Description |
|---|
MediaTracker(Component comp)
Creates a media tracker to track images for a given component.
|
| Modifier and Type | Method and Description |
|---|---|
void |
addImage(Image image,
int id)
Adds an image to the list of images being tracked by this media
tracker.
|
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.
|
boolean |
checkAll()
Checks to see if all images being tracked by this media tracker
have finished loading.
|
boolean |
checkAll(boolean load)
Checks to see if all images being tracked by this media tracker
have finished loading.
|
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.
|
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.
|
Object[] |
getErrorsAny()
Returns a list of all media that have encountered an error.
|
Object[] |
getErrorsID(int id)
Returns a list of media with the specified ID that
have encountered an error.
|
boolean |
isErrorAny()
Checks the error status of all of the images.
|
boolean |
isErrorID(int id)
Checks the error status of all of the images tracked by this
media tracker with the specified identifier.
|
void |
removeImage(Image image)
Removes the specified image from this media tracker.
|
void |
removeImage(Image image,
int id)
Removes the specified image from the specified tracking
ID of this media tracker.
|
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.
|
(package private) void |
setDone() |
int |
statusAll(boolean load)
Calculates and returns the bitwise inclusive OR of the
status of all media that are tracked by this media tracker.
|
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.
|
void |
waitForAll()
Starts loading all images tracked by this media tracker.
|
boolean |
waitForAll(long ms)
Starts loading all images tracked by this media tracker.
|
void |
waitForID(int id)
Starts loading all images tracked by this media tracker with the
specified identifier.
|
boolean |
waitForID(int id,
long ms)
Starts loading all images tracked by this media tracker with the
specified identifier.
|
Component target
Component that will be
tracked by a media tracker where the image will
eventually be drawn.MediaTracker(Component)MediaEntry head
Images that is being
tracked by the MediaTracker.addImage(Image, int),
removeImage(Image)public static final int LOADING
public static final int ABORTED
public static final int ERRORED
public static final int COMPLETE
static final int DONE
public MediaTracker(Component comp)
comp - the component on which the images
will eventually be drawnpublic void addImage(Image image, int id)
image - the image to be trackedid - an identifier used to track this imagepublic void addImage(Image image, int id, int w, int h)
image - the image to be trackedid - an identifier that can be used to track this imagew - the width at which the image is renderedh - the height at which the image is renderedpublic 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 otherwisecheckAll(boolean),
checkID(int),
isErrorAny(),
isErrorID(int)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.
load - if true, start loading any
images that are not yet being loadedtrue if all images have finished loading,
have been aborted, or have encountered
an error; false otherwisecheckID(int),
checkAll(),
isErrorAny(),
isErrorID(int)public boolean isErrorAny()
true if any of the images tracked
by this media tracker had an error during
loading; false otherwiseisErrorID(int),
getErrorsAny()public Object[] getErrorsAny()
null if
there are none with errorsisErrorAny(),
getErrorsID(int)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.
InterruptedException - if any thread has
interrupted this threadwaitForID(int),
waitForAll(long),
isErrorAny(),
isErrorID(int)public 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.
ms - the number of milliseconds to wait
for the loading to completetrue if all images were successfully
loaded; false otherwiseInterruptedException - if any thread has
interrupted this thread.waitForID(int),
waitForAll(long),
isErrorAny(),
isErrorID(int)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.
load - if true, start loading
any images that are not yet being loadedstatusID(int, boolean),
LOADING,
ABORTED,
ERRORED,
COMPLETEpublic 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.
id - the identifier of the images to checktrue if all images have finished loading,
have been aborted, or have encountered
an error; false otherwisecheckID(int, boolean),
checkAll(),
isErrorAny(),
isErrorID(int)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.
id - the identifier of the images to checkload - if true, start loading any
images that are not yet being loadedtrue if all images have finished loading,
have been aborted, or have encountered
an error; false otherwisecheckID(int, boolean),
checkAll(),
isErrorAny(),
isErrorID(int)public boolean isErrorID(int id)
id - the identifier of the images to checktrue if any of the images with the
specified identifier had an error during
loading; false otherwiseisErrorAny(),
getErrorsID(int)public Object[] getErrorsID(int id)
id - the identifier of the images to checknull if there are none with errorsisErrorID(int),
isErrorAny(),
getErrorsAny()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.
id - the identifier of the images to checkInterruptedException - if any thread has
interrupted this thread.waitForAll(),
isErrorAny(),
isErrorID(int)public 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.
id - the identifier of the images to checkms - the length of time, in milliseconds, to wait
for the loading to completeInterruptedException - if any thread has
interrupted this thread.waitForAll(),
waitForID(int),
statusID(int, boolean),
isErrorAny(),
isErrorID(int)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.
id - the identifier of the images to checkload - if true, start loading
any images that are not yet being loadedstatusAll(boolean),
LOADING,
ABORTED,
ERRORED,
COMPLETEpublic void removeImage(Image image)
image - the image to be removedremoveImage(java.awt.Image, int),
removeImage(java.awt.Image, int, int, int)public void removeImage(Image image, int id)
Image being tracked
under the specified ID are removed regardless of scale.image - the image to be removedid - the tracking ID frrom which to remove the imageremoveImage(java.awt.Image),
removeImage(java.awt.Image, int, int, int)public void removeImage(Image image, int id, int width, int height)
image - the image to be removedid - the tracking ID from which to remove the imagewidth - the width to remove (-1 for unscaled)height - the height to remove (-1 for unscaled)removeImage(java.awt.Image),
removeImage(java.awt.Image, int)void setDone()