label.java

j2me下的1套UI框架.包含j2me开发中会应用的各种低级组件

package com.jmobilecore.ui.core;

import javax.microedition.lcdui.Graphics;
import javax.microedition.lcdui.Font;

/**
 * Provides a text label for display on the screen.  A label is not focusable.
 *
 * @author Greg Gridin
 */
public class Label extends Component {

    /**
     * The text of this label.
     * @see #getText()
     * @see #setText(String)
     */
    protected String text;

    /**
     * Constructs a new label with the specified string of text,
     * left justified.
     * @param text the string that the label presents.
     *        A <code>null</code> value
     *        will be accepted without causing a NullPointerException
     *        to be thrown.
     *        The text can be single line only. If text contains
     *        \n characters (used to indicate line breaks)  then it might overlap with other UI components.
     *        It is up to the caller to ensure correctness of input string
     */
    public Label(String text) {
        this(text, Style.TEXT_FONT, LEFT);
    }

    /**
     * Constructs a new label that presents the specified string of
     * text with the specified alignment.
     * Possible values for <code>alignment</code> are <code>Label.LEFT</code>,
     * <code>Label.RIGHT</code>, and <code>Label.CENTER</code>.
     * @param text the string that the label presents.
     *        A <code>null</code> value
     *        will be accepted without causing a NullPointerException
     *        to be thrown.
     *        The text can be single line only. If text contains
     *        \n characters (used to indicate line breaks)  then it might overlap with other UI components.
     *        It is up to the caller to ensure correctness of input string
     * @param     alignment   the alignment value.
     */
    public Label(String text, int alignment) {
        this(text, Style.TEXT_FONT, alignment);
    }

    /**
     * Constructs a new label that presents the specified string of
     * text with the specified alignment.
     * Possible values for <code>alignment</code> are <code>Label.LEFT</code>,
     * <code>Label.RIGHT</code>, and <code>Label.CENTER</code>.
     * @param text the string that the label presents.
     *        A <code>null</code> value
     *        will be accepted without causing a NullPointerException
     *        to be thrown.
     *        The text can be single line only. If text contains
     *        \n characters (used to indicate line breaks)  then it might overlap with other UI components.
     *        It is up to the caller to ensure correctness of input string
     * @param  font   the label font
     * @param  alignment   the alignment value.
     */
    public Label(String text, Font font, int alignment) {
        this.font = font;
        setText(text);
        setFont(font);
        this.alignment = alignment;
    }

    /**
     * Paints the label to the screen.
     *
     * @param g The Graphics object to render to.
     */
    public void paint(Graphics g) {
        paintBackground(g);
        prepareForeground(g);
        int y = screenY + Style.V_GAP;
        if (alignment == LEFT) {
            g.drawString(text, Style.H_GAP, y, Graphics.TOP | Graphics.LEFT);
        } else if (alignment == RIGHT) {
            g.drawString(text, getWidth() - Style.H_GAP, y, Graphics.TOP | Graphics.RIGHT);
        } else if (alignment == CENTER) {
            g.drawString(text, getWidth() / 2, y, Graphics.TOP | Graphics.HCENTER);
        }
        super.paint(g);
    }

    /**
     * Gets the text of this label.
     * @return     the text of this label, or <code>null</code> if
     *             the text has been set to <code>null</code>.
     * @see        #setText
     */
    public String getText() {
        return text;
    }

    /**
     * Sets the text for this label to the specified text.
     * @param      text the text that this label displays.
     * @see        #getText
     */
    public void setText(String text) {
        this.text = text;
    }

    /**
     * Creates title label
     *
     * @param titleText The title text
     * @return title for current screen that could be uses with {@link ScreenCanvas#ScreenCanvas ScreenCanvas}
     * @see Label
     */
    static public Label createTitleLabel(String titleText) {

        Label title = new Label(titleText, Style.HEADER_FONT, Label.CENTER);
        title.background = Style.TITLE_BACKGROUND_COLOR;
        title.foreground = Style.TITLE_TEXT_COLOR;
        return title;
    }
} // class Label