stringitem.java

有关j2me的很好的例子可以研究一下

/*
 * @(#)StringItem.java	1.37 01/08/09
 * Copyright (c) 1999-2001 Sun Microsystems, Inc. All Rights Reserved.
 *
 * This software is the confidential and proprietary information of Sun
 * Microsystems, Inc. ("Confidential Information").  You shall not
 * disclose such Confidential Information and shall use it only in
 * accordance with the terms of the license agreement you entered into
 * with Sun.
 *
 * SUN MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF THE
 * SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
 * PURPOSE, OR NON-INFRINGEMENT. SUN SHALL NOT BE LIABLE FOR ANY DAMAGES
 * SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR DISTRIBUTING
 * THIS SOFTWARE OR ITS DERIVATIVES.
 */
package javax.microedition.lcdui;

/**
 * An item that can contain a string. A StringItem is display-only; the user
 * cannot edit the contents. Both the label and the textual content of a
 * StringItem may be modified by the application. The visual representation
 * of the label may differ from that of the textual contents.
 */
public class StringItem extends Item {

    /** The text of this StringItem */
    private String text;

    /**
     * Creates a new StringItem object with the given label and textual content.
     * Either label or text may be present or null.
     *
     * @param label the Item label
     * @param text the text contents
     */
    public StringItem(String label, String text) {
        super(label);

        // SYNC NOTE: Its clear we're only initializing instance variables
        // so ok to leave unlocked
        this.text = text;
        layouts = new Layout[1];
    }

    /**
     * Gets the text contents of the StringItem, or null if the StringItem is
     * empty.
     * @return a string with the content of the item
     *
     * @see #setText
     */
    public String getText() {
        // SYNC NOTE: return of atomic value, no locking necessary
        return text;
    }

    /**
     * Sets the text contents of the StringItem. If text is null, the StringItem
     * is set to be empty.
     * @param text the new content
     *
     * @see #getText
     */
    public void setText(String text) {
        synchronized (Display.LCDUILock) {
            this.text = text;
            handleContentChanged();
        }
    }

    /**
     * Sets the label of the Item. If label is null, specifies that this
     * item has no label.
     * @param label the label string
     */
    public void setLabel(String label) {
        synchronized (Display.LCDUILock) {
            super.setLabel(label);
            handleContentChanged();
        }
    }

    // package private

    /**
     * StringItems and ImageItems are grouped together.
     *
     * @param item  to be checked against
     * @return true if this Item and passed in item are part of the 
     *         same group, otherwise false is returned
     */
    boolean isGrouped(Item item) {
        if (item != null && item.isGroupable()) {
            return item.layouts[0] == layouts[0];
        }

        return false;
    }

    /**
     * Determines if that item can be grouped with other items in a
     * common layout.
     * @return true if this item can be grouped with others; 
     *         false - otherwise
     */
    boolean isGroupable() {
        return true;
    }

    /**
     * Determine if this StringItem takes focus
     *
     * @return boolean True, if this StringItem can take the focus
     */
    boolean takesFocus() {
        return false;
    }

    /**
     * Get the height of this StringItem
     *
     * @return int The height (in pixels) of this StringItem
     */
    int getHeight() {
        if (layouts[0] == null) {
            return 0;
        }

        return layouts[0].getHeight();
    }

    /**
     * Set the width for this StringItem
     *
     * @param width The allowable width
     * @return int The height required to display this StringItem given
     *              the allowable width
     */
    int setWidth(int width) {
        if (layouts[0] == null) {
            return 0;
        }

        return layouts[0].setWidth(width);
    }

    /**
     * Paint this StringItem
     *
     * @param g The Graphics object to paint to
     */
    void paint(Graphics g) {
        if (layouts[0] != null) {
            layouts[0].paint(g, true, false);
        }
    }

    // private

    /**
     * Handle a content change
     */
    private void handleContentChanged() {
        if (!initLayoutDone() || layouts[0] == null) {
            return;
        }

        contentChanged(0, 0,
            ((TaGLayout)layouts[0]).itemContentChanged(this));

    }

}