java.lang.Object java.awt.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:
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); } } }
Field Summary | |
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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. |
static int |
ERRORED
Flag indicating that the downloading of media encountered an error. |
static int |
LOADING
Flag indicating that media is currently being loaded. |
Constructor Summary | |
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MediaTracker
(
Component
comp) Creates a media tracker to track images for a given component. |
Method Summary | |
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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. |
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. |
Methods inherited from class java.lang. Object |
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clone , equals , finalize , getClass , hashCode , notify , notifyAll , toString , wait , wait , wait |
Field Detail |
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public static final int LOADING
public static final int ABORTED
public static final int ERRORED
public static final int COMPLETE
Constructor Detail |
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public MediaTracker(Component comp)
Method Detail |
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public void addImage(Image image, int id)
public void addImage(Image image, int id, int w, int h)
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.
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.
public boolean isErrorAny()
public Object[] getErrorsAny()
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.
public boolean waitForAll(long ms) 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.
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.
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.
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.
public boolean isErrorID(int id)
public Object[] getErrorsID(int id)
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.
public boolean waitForID(int id, long ms) throws InterruptedException
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.
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.
public void removeImage(Image image)
public void removeImage(Image image, int id)
public void removeImage(Image image, int id, int width, int height)