java.lang.Object java.awt.MediaTracker
public class MediaTracker
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);
}
}
}
static int ABORTED
static int COMPLETE
static int ERRORED
static int LOADING
MediaTracker(Component comp)
void addImage(Image image, int id)
void addImage(Image image, int id, int w, int h)
boolean checkAll()
boolean checkAll(boolean load)
boolean checkID(int id)
boolean checkID(int id, boolean load)
Object[] getErrorsAny()
Object[] getErrorsID(int id)
boolean isErrorAny()
boolean isErrorID(int id)
void removeImage(Image image)
void removeImage(Image image, int id)
void removeImage(Image image, int id, int width, int height)
int statusAll(boolean load)
int statusID(int id, boolean load)
void waitForAll()
boolean waitForAll(long ms)
void waitForID(int id)
boolean waitForID(int id, long ms)
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait LOADING
public static final int LOADING
statusAll(boolean), statusID(int, boolean), Constant Field Values
public static final int ABORTED
statusAll(boolean), statusID(int, boolean), Constant Field Values
public static final int ERRORED
statusAll(boolean), statusID(int, boolean), Constant Field Values
public static final int COMPLETE
statusAll(boolean), statusID(int, boolean), Constant Field Values
public MediaTracker(Component comp)
comp - the component on which the images will eventually be drawn
public void addImage(Image image,
int id)
image - the image to be tracked
id - an identifier used to track this image
public void addImage(Image image,
int id,
int w,
int h)
image - the image to be tracked
id - an identifier that can be used to track this image
w - the width at which the image is rendered
h - the height at which the image is rendered
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(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 loaded
true if all images have finished loading, have been aborted, or have encountered an error; false otherwise
checkID(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 otherwise
isErrorID(int), getErrorsAny()
public Object[] getErrorsAny()
null if there are none with errors
isErrorAny(), 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 another thread has interrupted this thread
waitForID(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 complete
true if all images were successfully loaded; false otherwise
InterruptedException - if another 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 loaded
statusID(int, boolean), LOADING, ABORTED, ERRORED, COMPLETE
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.
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
checkID(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 check
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
checkID(int, boolean), checkAll(), isErrorAny(), isErrorID(int)
public boolean isErrorID(int id)
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
isErrorAny(), getErrorsID(int)
public Object[] getErrorsID(int id)
id - the identifier of the images to check
null if there are none with errors
isErrorID(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 check
InterruptedException - if another 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 check
ms - the length of time, in milliseconds, to wait for the loading to complete
InterruptedException - if another 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 check
load - if true, start loading any images that are not yet being loaded
statusAll(boolean), LOADING, ABORTED, ERRORED, COMPLETE
public void removeImage(Image image)
image - the image to be removed
removeImage(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 removed
id - the tracking ID frrom which to remove the image
removeImage(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 removed
id - the tracking ID from which to remove the image
width - the width to remove (-1 for unscaled)
height - the height to remove (-1 for unscaled)
removeImage(java.awt.Image), removeImage(java.awt.Image, int)
Copyright © 2004, 2010 Oracle and/or its affiliates. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.
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