alert.java

有关j2me的很好的例子可以研究一下

     * @param cmd the Command
     *
     * @throws IllegalStateException always
     */
    public void addCommand(Command cmd) {
        // SYNC NOTE: no sync necessary
        throw new IllegalStateException();
    }

    /**
     * Listeners are not allowed on Alerts, so this method will always throw
     * IllegalStateException whenever it is called.
     *
     * @param l the Listener
     * @throws IllegalStateException always
     */
    public void setCommandListener(CommandListener l) {
        // SYNC NOTE: no sync necessary
        throw new IllegalStateException();
    }

    // package private

    /**
     * Static default Command for "OK"
     */
    static final Command OK = new Command(Resource.getString("Done"),
                                          Command.OK, 0);

    /**
     * Special CommandListener instance to handle execution of
     * the default "OK" Command
     */
    CommandListener implicitListener = new CommandListener() {
        /**
         * Handle the execution of the given Command and Displayable.
         *
         * @param c The Command to execute
         * @param s The Displayable from which the Command originated
         */
        public void commandAction(Command c, Displayable s) {
            if (c == OK) {
                synchronized (Display.LCDUILock) {
                    currentDisplay.clearAlert();
                }
            }
        }
    };

    /**
     * Notify this Alert that is being displayed on the
     * given Display and wether it needs to initialize its
     * highlight
     *
     * @param d The Display this Alert will be shown on
     */
    void showNotifyImpl(Display d) {
        super.showNotifyImpl(d);
        if (getTimeout() == FOREVER) {
            super.addCommandImpl(OK);
            super.setCommandListener(implicitListener);
        }
    }

    /**
     * Notify this Alert that it will no longer be displayed
     * on the given Display
     *
     * @param d The Display showing this Alert
     */
    void hideNotifyImpl(Display d) {
        super.hideNotifyImpl(d);
        super.removeCommandImpl(OK);
        super.setCommandListener(null);
    }

    /**
     * Paint the contents of this Alert given the graphics context.
     *
     * @param g The Graphics object to paint this Alert to
     */
    void paintContent(Graphics g) {
        // clear the screen area for the image & text
        g.setColor(Display.ERASE_COLOR);
        g.fillRect(g.getClipX(), g.getClipY(), 
                   g.getClipWidth(), g.getClipHeight());

        // offset to vertically center the alert content if the alert height
        // is less than the view port height.
        int yOffset = (viewPortHeight - alertHeight) / 2;
        if (yOffset < 0) {
            yOffset = 0;
        }

        // center and paint the image
        if (alertImage != null) {
            int xOffset = (viewPortWidth - alertImage.getWidth()) / 2;
            if (xOffset < 0) {
                xOffset = 0;
            }

            g.drawImage(alertImage, xOffset, yOffset, 
                        Graphics.TOP | Graphics.LEFT);
        }

        // paint the text
        if (alertText != null) {
            g.translate(0, imgHeight + yOffset);
            alertText.paint(g, false, false);
        }
    }

    /**
     * Layout the content of this Alert given the width and
     * height parameters
     *
     * @param w The allowed width of this Alert
     * @param h The allowed height of this Alert
     * @return int  The height this Alert will require given the allowable
     *              width
     */
    int layoutContent(int w, int h) {
        // layout the alert text 
        alertHeight = 0;
        if (alertText != null) {
            alertHeight += alertText.setWidth(w);
        }

        // update the alert height
        alertHeight += imgHeight;
        return alertHeight;
    }

    //
    // Private fields
    //

    /**
     * The default timeout of all alerts
     */
    private static final int DEFAULT_TIMEOUT = 2000;

    /**
     * The timeout value of this alert
     */
    private int time;

    /**
     * The type of this alert
     */
    private AlertType type;

    /**
     * The layout object for the alert text string
     */
    private StringLayout alertText;

    /**
     * The image of this alert
     */
    private Image alertImage;

    /**
     * The height of this alert image
     */
    private int imgHeight;

    /**
     * The height of this alert
     */
    private int alertHeight;

    /**
     * Set the image displayed by this Alert
     *
     * @param img   The new Image to be displayed by this Alert
     */
    private void setImageImpl(Image img) {
        Image currentImg = getImage();

        // Don't do anything if nothing is changed.
        // The check is only if the image object reference is the same.
        // There is no image comparison for 2 different image object
        // reference, even though they could be the same image.
        if (((currentImg == null) && (img == null)) ||
                ((currentImg != null) && (img != null) &&
                (currentImg == img))) {
            return;
        }

        if ((img != null) && img.isMutable()) {
            throw new IllegalArgumentException();
        }

        int newImageHeight = (img == null) ? 0 : img.getHeight();

        this.alertImage = img;
        contentChanged(null, 0, 0, newImageHeight - imgHeight);

        // update the alert and image height
        alertHeight += (newImageHeight - imgHeight);
        imgHeight = newImageHeight;
    }

    /**
     * Set the message displayed by this Alert
     *
     * @param str   The new message to be displayed by this Alert
     */
    private void setStringImpl(String str) {
        String currentStr = getStringImpl();

        // don't do anything if nothing is changed
        if (((currentStr == null) && (str == null)) ||
            ((currentStr != null) && (str != null) && currentStr.equals(str))) {
            return;
        }

        int deltaHeight = 0;

        if (this.alertText == null) {
            this.alertText = new StringLayout(str, CONTENT_FONT);

            if (initLayoutDone()) {
                deltaHeight = this.alertText.setWidth(viewPortWidth);
            }
        } else {
            deltaHeight = alertText.setString(str);
        }

        // update the alert height
        alertHeight += deltaHeight;

        contentChanged(null, 0, 0, deltaHeight);
    }

    /**
     * Get the message displayed by this Alert
     *
     * @return String The message displayed by this Alert
     */
    private String getStringImpl() {
        return (alertText == null ? null : alertText.getString());
    }
}