screencanvas.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.*;
import java.util.Vector;

/**
 * A screen that contains {@link Component}s.
 *
 * @author Greg Gridin
 */
public class ScreenCanvas extends PlatformCanvas {

    /**
     * Off the screen image for double buffer painting
     */
    protected Image offScreen;

    /**
     * Scrolling direction. Used with {@link #drawTriangle drawTriangle}
     */
    public final static int SCROLL_UP = 0x0001;

    /**
     * Scrolling direction. Used with {@link #drawTriangle drawTriangle}
     */
    public final static int SCROLL_DOWN = 0x0002;

    /**
     * Scrolling step
     */
    protected final static int CANVAS_SCROLL_STEP = 10;

    /**
     * Screen title
     */
    protected Label screenTitle;

    /**
     * Vector of GUI components
     */
    protected Vector components = null;

    /**
     * SoftKeyBar for current screen
     * this component is not in components vector
     */
    protected SoftKeyBar softKeyBar = null;

    /**
     * Currently focused component. Index points to components vector
     */
    protected int focusedIndex = -1;

    /**
     * y-coordinate offset within the body of the first component to display. For
     * example, if the screen container contains more components than can be
     * displayed at one time vertically, this offset will be adjusted to ensure
     * that the screen is scrolled to always display the currently-focused
     * component.
     */
    protected int bodyOffset = 0;

    /**
     * Indicated if focus ajjustment is required
     *
     * @see #recalcAdjustment
     * @see #refocus
     */
    protected boolean adjustFocus = false;

    /**
     * Creates a new <code>ScreenCanvas</code> instance.
     */
    public ScreenCanvas() {
        this(null, new SoftKeyBar());
    }

    /**
     * Creates a new <code>ScreenCanvas</code> instance.
     *
     * @param title The screen title, one line text
     */
    public ScreenCanvas(Label title) {
        this(title, new SoftKeyBar());
    }

    /**
     * Creates a new <code>ScreenCanvas</code> instance.
     *
     * @param title      Title for current screen
     * @param softKeyBar Container for soft keys for current screen
     */
    public ScreenCanvas(Label title, SoftKeyBar softKeyBar) {

        screenTitle = title;
        components = new Vector();
        this.softKeyBar = softKeyBar;
        if (!DOUBLE_BUFFER) {
            offScreen = Image.createImage(WIDTH, HEIGHT);
        }
    }

    /**
     * Height of the title in pixels
     */
    protected int titleHeight;

    /**
     * Height of the scrollbar in pixels
     */
    protected int softKeyBarHeight;

    /**
     * Height of the scrollable area (of current screen) in pixels
     */
    protected int paintAreaHeight;

    /**
     * Paints the screen's body, which is all of the components that have been
     * added to the screen.
     *
     * @param g Graphics context
     */
    public void paint(Graphics g) {

        Graphics saved = g;
        int oldColor = g.getColor();
        if (offScreen != null) {
            g = offScreen.getGraphics();
        }

        titleHeight = (screenTitle != null) ? screenTitle.height : 0;
        softKeyBarHeight = (softKeyBar != null) ? softKeyBar.height : 0;
        paintAreaHeight = HEIGHT - titleHeight - softKeyBarHeight;
        g.setClip(0, 0, WIDTH, HEIGHT);
        paintBodyBackground(g);
        paintBody(g);
        if (screenTitle != null) screenTitle.paint(g);
        if (softKeyBar != null) softKeyBar.paint(g);
        paintScroller(g);

        g.setColor(oldColor);
        if (g != saved) {
            saved.drawImage(offScreen, 0, 0, Graphics.LEFT | Graphics.TOP);
        }
        saved = null;
    }

    /**
     * Paints the screen's body background
     *
     * @param g Graphics context
     */
    protected void paintBodyBackground(Graphics g) {
        g.setColor(Style.BACKGROUND_COLOR);
        g.fillRect(0, titleHeight, WIDTH, paintAreaHeight);
    }

    /**
     * Paint scrolling indicator(s) at the bottom of the screen to indicate that
     * the display can scroll vertically.
     *
     * @param g Graphics context
     */
    protected void paintScroller(Graphics g) {
        int scrollDirections = getScrollDirections();
        int arrowMaxHeight = softKeyBarHeight / 2 - 1;
        if ((scrollDirections & SCROLL_UP) > 0) {
            ScreenCanvas.drawTriangle(g, WIDTH / 2,
                    HEIGHT - softKeyBarHeight, arrowMaxHeight,
                    SCROLL_UP, Style.ARROW_COLOR);
        }
        if ((scrollDirections & SCROLL_DOWN) > 0) {
            ScreenCanvas.drawTriangle(g, WIDTH / 2,
                    HEIGHT - 1, arrowMaxHeight,
                    SCROLL_DOWN, Style.ARROW_COLOR);
        }
    }

    /**
     * Support method for painting scroller
     *
     * @see #paintScroller
     */
    public static void drawTriangle(Graphics g,
                                    int tipX, int tipY,
                                    int maxHeight,
                                    int direction,
                                    int color) {

        int yIncrement = 1;
        if (direction == ScreenCanvas.SCROLL_DOWN) yIncrement = -1;

        if (color!=Color.TRANSPARENT) g.setColor(color);
        for (int height = 0; height < maxHeight; height++) {
            g.drawLine(tipX, tipY, tipX + height * 2, tipY);
            tipX--; // start one pixel over
            tipY += yIncrement; // next row to draw
        }
    }

    /**
     * Processes a press of a key.
     */
    protected void keyPressed(int keyCode) {

        if (softKeyBar != null && softKeyBar.keyPressed(keyCode))
            return;

        if (focusedIndex >= 0 && focusedIndex < components.size()) {
            Component focusedComponent = (Component) components.elementAt(focusedIndex);
            if (focusedComponent.keyPressed(keyCode)) return;
        }

        int n = -1;
        if (keyCode == KEY_UP) {
            if ((n = getPreviousFocusable()) != -1) {
                changeFocus(n);
            } else {
                scrollUp();
            }
        } else if (keyCode == KEY_DOWN) {
            if ((n = getNextFocusable()) != -1) {
                changeFocus(n);
            } else {
                scrollDown();
            }
        }
    }

    /**
     * Returns the directions the body can be scrolled in.
     * This should be dynamic depending upon what portion of the body area is
     * displayed.
     *
     * @return The directions that the body area can be scrolled. Should be 0 if
     *         all body elements can be displayed at once, but if not it should be an
     *         appropriate bitwise or of {@link #SCROLL_UP} and/or {@link #SCROLL_DOWN}
     */
    protected int getScrollDirections() {
        int directions = 0;
        if (bodyOffset > 0) directions |= SCROLL_UP;
        if (bodyOffset + paintAreaHeight < getComponentsHeight())
            directions |= SCROLL_DOWN;
        return directions;
    }

    /**
     * Adds the component to the screen.
     * <p/>
     * More presicely it adds a component to vector of components for current screen
     * Components are displayed in order of {@link #components} one component per line
     *
     * @param component the component to be added
     */
    public void add(Component component) {
        component.parentScreen = this;
        components.addElement(component);
        if (component.focusable && focusedIndex == -1) {
            component.requestFocus();
            focusedIndex = components.size() - 1;
        }
    }

    /**
     * Adds the component to the screen at the given position.
     * <p/>
     * More presicely it adds a component to vector of components for current screen
     * Components are displayed in order of {@link #components} one component per line
     *
     * @param component the component to be added
     * @param index     the position at which to insert the component,
     *                  or <code>-1</code> to append the component to the end
     */
    public void add(Component component, int index) {
        if (index == -1) {
            add(component);
        } else {
            component.parentScreen = this;
            components.insertElementAt(component, index);
            if (focusedIndex == -1) {
                if (component.focusable) {