canvashelper.java

BTBrowser,用JAVA API实现蓝牙通信.

package org.klings.wireless.j2me;

import java.util.Vector;

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

/**
 * Formats <code>String</code>s so they can be printed in a
 * <code>Canvas</code> without exceeding the <code>Canvas</code> width.
 */
public class CanvasHelper {

	/**
	 * Splits a <code>String</code>. Each fragment will not be longer than
	 * maxWidth when printed with the <code>Font</code> font.
	 * 
	 * @param s
	 *            The <code>String</code> to chop.
	 * @param font
	 *            The <code>Font</code> used when calculating <code>String
	 * </code>
	 *            lengths.
	 * 
	 * @param maxWidth
	 *            The maximum width of the resulting strings measured in pixels.
	 * 
	 * @return <code>String</code> array containing one or more formatted
	 *         strings. <code>null</code> if the supplied <code>String</code>
	 *         or <code>
	 * Font</code> is <code>null</code>
	 */
	public static String[] splitString(String s, Font font, int maxWidth) {
		if (s == null || font == null)
			return null;
		/* Return String immediately if it does not need formatting */
		if (font.stringWidth(s) < maxWidth) {
			String[] res = { s };
			return res;
		}
		maxWidth -= font.charWidth('i');
		/*
		 * Compute avg. number of characters on a line by getting the average
		 * between the 'i' and 'M';
		 */
		int avgChars = maxWidth
				/ ((font.charWidth('i') + font.charWidth('M')) / 2);
		int offset1 = 0;
		int len = 0;
		boolean longer = false;
		boolean keepOn = false;
		Vector v = new Vector();
		while (s != null) {
			/* The remaining String is short enough, so we are done */
			if (font.stringWidth(s) < maxWidth) {
				v.addElement(s);
				s = null;
				break;
			}
			/*
			 * Check that the String length is bigger than avgChars to avoid
			 * nullpointer exception.
			 */
			len = s.length();
			if (len > avgChars)
				len = avgChars;
			/*
			 * If the String is to short, make it longer. Else make it shorter.
			 */
			if (font.substringWidth(s, 0, len) < maxWidth) {
				len++;
				while (font.substringWidth(s, 0, len++) < maxWidth) {
				}
				v.addElement(s.substring(0, len - 1));
				s = s.substring(len - 1);
			} else {
				len--;
				while (font.substringWidth(s, 0, len) > maxWidth)
					len--;
				v.addElement(s.substring(0, len));
				s = s.substring(len);
			}
		}
		/*
		 * Copy the results from the Vector to a String array and return the
		 * results.
		 */
		String[] result = new String[v.size()];
		for (int i = 0; i < result.length; i++) {
			result[i] = (String) v.elementAt(i);
		}
		return result;
	}

	/**
	 * Formats and prints a <code>String</code>, possibly over several lines.
	 * 
	 * @param s
	 *            The <code>String</code> to be printed.
	 * @param x
	 *            The x coordinate of the anchor point.
	 * @param y
	 *            The y coordinate of the anchor point.
	 * @param anchor
	 *            The anchor point for positioning the text.
	 * @param f
	 *            The <code>Font</code> to be used when drawing the text.
	 * @param maxWidth
	 *            Maximum width of the strings, measured in pixels.
	 * @param g
	 *            The <code>Graphics</code> object used when drawing text.
	 * @return The number of pixels used to draw the text in the y direction,
	 *         given by: number of lines drawn * the <code>Font</code> height.
	 * @see javax.microedition.lcdui.Graphics#drawString(String str,int x, int
	 *      y,int anchor)
	 */

	public static int printString(String s, int x, int y, int anchor, Font f,
			int maxWidth, Graphics g) {
		int yDelta = 0;
		int fontHeight = f.getHeight();
		g.setFont(f);
		/*
		 * If the String does not need formatting, just print it. Else, chop it
		 * and print the Strings from the returned array.
		 */
		if (f.stringWidth(s) < maxWidth) {
			g.drawString(s, x, y, anchor);
			yDelta = fontHeight;
		} else {
			String[] content = splitString(s, f, maxWidth);
			for (int i = 0; i < content.length; i++) {
				g.drawString(content[i], x, y + yDelta, anchor);
				yDelta += fontHeight;
			}
		}
		/* Return the amount of pixels we have moved in the y direction */
		return yDelta;
	}

}