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Class java.awt.MediaTracker - JDK 5 Documentation v1.1.8, Java 2 SDK 英文文档

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Class java.awt.MediaTracker 

java.lang.Object
   |
   +----java.awt.MediaTracker
public class MediaTracker
extends Object
implements Serializable
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.

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);
	    }
	}
 }

Variable Index

o ABORTED
Flag indicating that the downloading of some media was aborted.
o COMPLETE
Flag indicating that the downloading of media was completed successfully.
o ERRORED
Flag indicating that the downloading of some media encountered an error.
o LOADING
Flag indicating some media is currently being loaded.

Constructor Index

o MediaTracker(Component)
Creates a media tracker to track images for a given component.

Method Index

o addImage(Image, int)
Adds an image to the list of images being tracked by this media tracker.
o addImage(Image, int, int, int)
Adds a scaled image to the list of images being tracked by this media tracker.
o checkAll()
Checks to see if all images being tracked by this media tracker have finished loading.
o checkAll(boolean)
Checks to see if all images being tracked by this media tracker have finished loading.
o checkID(int)
Checks to see if all images tracked by this media tracker that are tagged with the specified identifier have finished loading.
o checkID(int, boolean)
Checks to see if all images tracked by this media tracker that are tagged with the specified identifier have finished loading.
o getErrorsAny()
Returns a list of all media that have encountered an error.
o getErrorsID(int)
Returns a list of media with the specified ID that have encountered an error.
o isErrorAny()
Checks the error status of all of the images.
o isErrorID(int)
Checks the error status of all of the images tracked by this media tracker with the specified identifier.
o removeImage(Image)
Remove the specified image from this media tracker.
o removeImage(Image, int)
Remove the specified image from the specified tracking ID of this media tracker.
o removeImage(Image, int, int, int)
Remove the specified image with the specified width, height, and ID from this media tracker.
o statusAll(boolean)
Calculates and returns the bitwise inclusive OR of the status of all media that are tracked by this media tracker.
o statusID(int, boolean)
Calculates and returns the bitwise inclusive OR of the status of all media with the specified identifier that are tracked by this media tracker.
o waitForAll()
Starts loading all images tracked by this media tracker.
o waitForAll(long)
Starts loading all images tracked by this media tracker.
o waitForID(int)
Starts loading all images tracked by this media tracker with the specified identifier.
o waitForID(int, long)
Starts loading all images tracked by this media tracker with the specified identifier.

Variables

o LOADING 
 public static final int LOADING
Flag indicating some media is currently being loaded.

See Also:
statusAll, statusID
o ABORTED 
 public static final int ABORTED
Flag indicating that the downloading of some media was aborted.

See Also:
statusAll, statusID
o ERRORED 
 public static final int ERRORED
Flag indicating that the downloading of some media encountered an error.

See Also:
statusAll, statusID
o COMPLETE 
 public static final int COMPLETE
Flag indicating that the downloading of media was completed successfully.

See Also:
statusAll, statusID

Constructors

o MediaTracker 
 public MediaTracker(Component comp)
Creates a media tracker to track images for a given component.

Parameters:
comp - the component on which the images will eventually be drawn.

Methods

o addImage 
 public void addImage(Image image,
                      int id)
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.
id - an identifier used to track this image.
o addImage 
 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. The image will eventually be rendered at the indicated width and height.

Parameters:
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.
o checkAll 
 public boolean checkAll()
Checks to see if all images being tracked by this media tracker 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.

Returns:
true if all images have finished loading, have been aborted, or have encountered an error; false otherwise.
See Also:
checkAll, checkID, isErrorAny, isErrorID
o checkAll 
 public boolean checkAll(boolean load)
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.
Returns:
true if all images have finished loading, have been aborted, or have encountered an error; false otherwise.
See Also:
checkID, checkAll, isErrorAny, isErrorID
o isErrorAny 
 public synchronized boolean isErrorAny()
Checks the error status of all of the images.

Returns:
true if any of the images tracked by this media tracker had an error during loading; false otherwise.
See Also:
isErrorID, getErrorsAny
o getErrorsAny 
 public synchronized Object[] getErrorsAny()
Returns a list of all media that have encountered an error.

Returns:
an array of media objects tracked by this media tracker that have encountered an error, or null if there are none with errors.
See Also:
isErrorAny, getErrorsID
o waitForAll 
 public void waitForAll() throws InterruptedException
Starts loading all images tracked by this media tracker. This method waits until all the images being tracked have finished 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.

Throws: InterruptedException
if another thread has interrupted this thread.
See Also:
waitForID, waitForAll, isErrorAny, isErrorID
o waitForAll 
 public synchronized boolean waitForAll(long ms) throws InterruptedException
Starts loading all images tracked by this media tracker. This method waits until all the images being tracked have finished loading, or until the length of time specified in milliseconds by the 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.

Parameters:
ms - the number of milliseconds to wait for the loading to complete.
Returns:
true if all images were successfully loaded; false otherwise.
Throws: InterruptedException
if another thread has interrupted this thread.
See Also:
waitForID, waitForAll, isErrorAny, isErrorID
o statusAll 
 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.

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:
load - if true, start loading any images that are not yet being loaded.
Returns:
the bitwise inclusive OR of the status of all of the media being tracked.
See Also:
statusID, LOADING, ABORTED, ERRORED, COMPLETE
o checkID 
 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.

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.
Returns:
true if all images have finished loading, have been aborted, or have encountered an error; false otherwise.
See Also:
checkID, checkAll, isErrorAny, isErrorID
o checkID 
 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.

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.
load - if true, start loading any images that are not yet being loaded.
Returns:
true if all images have finished loading, have been aborted, or have encountered an error; false otherwise.
See Also:
checkID, checkAll, isErrorAny, isErrorID
o isErrorID 
 public synchronized boolean isErrorID(int id)
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.
Returns:
true if any of the images with the specified identifier had an error during loading; false otherwise.
See Also:
isErrorAny, getErrorsID
o getErrorsID 
 public synchronized Object[] getErrorsID(int id)
Returns a list of media with the specified ID that have encountered an error.

Parameters:
id - the identifier of the images to check.
Returns:
an array of media objects tracked by this media tracker with the specified identifier that have encountered an error, or null if there are none with errors.
See Also:
isErrorID, isErrorAny, getErrorsAny
o waitForID 
 public void waitForID(int id) throws InterruptedException
Starts loading all images tracked by this media tracker with the specified identifier. This method waits until all the images with the specified identifier have finished loading.

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.

Parameters:
id - the identifier of the images to check.
Throws: InterruptedException
if another thread has interrupted this thread.
See Also:
waitForAll, isErrorAny, isErrorID
o waitForID 
 public synchronized boolean waitForID(int id,
                                       long ms) throws InterruptedException
Starts loading all images tracked by this media tracker with the specified identifier. This method waits until all the images with the specified identifier have finished loading, or until the length of time specified in milliseconds by the 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.

Parameters:
id - the identifier of the images to check.
ms - the length of time, in milliseconds, to wait for the loading to complete.
Throws: InterruptedException
if another thread has interrupted this thread.
See Also:
waitForAll, waitForID, statusID, isErrorAny, isErrorID
o statusID 
 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.

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.
load - if true, start loading any images that are not yet being loaded.
Returns:
the bitwise inclusive OR of the status of all of the media with the specified identifier that are being tracked.
See Also:
statusAll, LOADING, ABORTED, ERRORED, COMPLETE
o removeImage 
 public synchronized void removeImage(Image image)
Remove the specified image from this media tracker. All instances of the specified image are removed, regardless of scale or ID.

Parameters:
image - the image to be removed
See Also:
removeImage, removeImage
o removeImage 
 public synchronized void removeImage(Image image,
                                      int id)
Remove the specified image from the specified tracking ID of this media tracker. All instances of Image being tracked under the specified ID are removed regardless of scale.

Parameters:
image - the image to be removed.
id - the tracking ID frrom which to remove the image.
See Also:
removeImage, removeImage
o removeImage 
 public synchronized void removeImage(Image image,
                                      int id,
                                      int width,
                                      int height)
Remove 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
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).
See Also:
removeImage, removeImage 
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