passtextpolicy.java

有关j2me的很好的例子可以研究一下

/*
 * @(#)PassTextPolicy.java	1.37 01/08/21
 * 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;

/**
 * A special policy to handle password text
 */
class PassTextPolicy extends Policy {

    /** The echo character buffer */
    private char[] echoCharLine;
    /** The number of echo chararcters allowed per line */
    private int numEchoCharsPerLine;
    /** The number of lines */
    private int numLines;
    /** The character used to echo to the display '*' by default */
    private final static char ECHO_CHAR = '*';
    /** The echo character pixel width, and extra space width */
    private int echoCharWidth, extraSpace;

    /**
     * Construct a new PassTextPolicy
     *
     * @param f The Font to use in this policy
     */
    PassTextPolicy(Font f) {
        this(f, 'W');
    }

    /**
     * Construct a new PassTextPolicy
     *
     * @param f The Font to use in this policy
     * @param extraSpaceChar The character to use for extra space
     */
    PassTextPolicy(Font f, char extraSpaceChar) {
        super(f);
        echoCharWidth = f.charWidth(ECHO_CHAR);
        extraSpace = f.charWidth(extraSpaceChar) - echoCharWidth;
        if (extraSpace < 0) {
            extraSpace = 0;
        }
    }

    /**
     * Set the width of this policy
     *
     * @param width
     * @param buf
     * @param numChars
     * @param curPos
     * @return int
     */
    int setWidth(int width, char[] buf, int numChars, int curPos) {
        numEchoCharsPerLine = (width - extraSpace) / echoCharWidth;
        echoCharLine = new char[numEchoCharsPerLine];
        for (int i = 0; i < numEchoCharsPerLine; i++) {
            echoCharLine[i] = ECHO_CHAR;
        }

        return super.setWidth(width, buf, numChars, curPos);
    }

    /**
     * Signal this policy that its content has changed
     *
     * @param buf
     * @param numChars
     * @param fromPos
     * @param curPos
     * @return int
     */
    int contentChanged(char[] buf, int numChars, int fromPos, int curPos) {
        if (width == -1) {
            return 0;
        }

        int oldHeight = height;

        numLines = (numChars+numEchoCharsPerLine-1)/numEchoCharsPerLine;
        height = numLines * lineHeight;
        if (height < lineHeight) {
            height = lineHeight;
        }
        
        cursorX = curPos%numEchoCharsPerLine * echoCharWidth;
        cursorY = curPos/numEchoCharsPerLine * lineHeight;
        
        if (curPos == numChars && cursorX == 0 && cursorY > 0) {
            cursorX = numEchoCharsPerLine * echoCharWidth;
            cursorY -= lineHeight;
        }
        return (height - oldHeight);
    }

    /**
     * Paint this policy
     *
     * @param g The Graphics object to paint to
     * @param buf The data buffer
     * @param numChars The number of characters in the buffer
     * @param cursorEnabled A boolean flag indicating the enabled state
     *                      of the cursor
     * @param cursorPos The location of the cursor
     * @param noCharShow A boolean flag to not display the characters on
     *                   the screen
     */
    void paint(Graphics g, char[] buf, int numChars, boolean cursorEnabled, 
               int cursorPos, boolean noCharShow) {

        // We assume that background was cleared with erase color
        g.setColor(Display.FG_COLOR);

        g.setFont(f);

        if (numChars > 0) {
            int echoCharSecWidth = 0;
        
            int y = g.getClipY();
            int yEnd = y + g.getClipHeight();
            int from = 0;
            if (y > 0) { 
                from = y / lineHeight;
            }

            y = from * lineHeight;
            for (int i = from; i < numLines-1 && y < yEnd;
                 ++i, y += lineHeight) {
                g.drawChars(echoCharLine, 0, numEchoCharsPerLine,
                            0, y, Graphics.TOP | Graphics.LEFT);
            }

            int n = numChars % numEchoCharsPerLine;
            if (n == 0) {
                n = numEchoCharsPerLine;
            }

            if (cursorEnabled || noCharShow) {
                g.drawChars(echoCharLine, 0, n, 0, y, 
                            Graphics.TOP | Graphics.LEFT);
            } else { // draw the one visible char
                if (n > 1) {
                    g.drawChars(echoCharLine, 0, n-1, 0, y, 
                                Graphics.TOP | Graphics.LEFT);
                }
		
		if (cursorX > echoCharWidth) {
		    g.drawChar(buf[numChars-1], cursorX-echoCharWidth, y,
			       Graphics.TOP | Graphics.LEFT);
		} else {
		    g.drawChar(buf[numChars-1], 0, y,
			       Graphics.TOP | Graphics.LEFT);
		}
            }
        }
        if (cursorEnabled) {
            g.drawLine(cursorX, cursorY, cursorX, cursorY + lineHeight);

        }
    }

    /**
     * Get the maximum width for this policy
     *
     * @param allowedWidth The default allowed width
     * @param maxSize ??
     * @return int The allowed width of this policy
     */
    int getMaxWidth(int allowedWidth, int maxSize) {
        // last character could be painted as other than 
        // an echo character during the input
        int w = echoCharWidth*maxSize + extraSpace;

        if (w < allowedWidth) {
            return w;
        }
        return allowedWidth;
    }
}