Image in button - j2me

问题:

I am trying to build a simple menu-based GUI with J2ME. The menu entries are currently objects of classes derived from the class Button. Is there any way I can:

1. Replace the text in the button and have an image show instead, sort of an icon?

2. Make the text and image appear side by side on the same menu bar.

If my question is not clear, please let me know and I will edit it.

回答1:

You can create your own Item that looks like a button by extending the CustomItem class.

This is a working MIDlet with a good MyButton class:

import javax.microedition.lcdui.Canvas;
import javax.microedition.lcdui.CustomItem;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Form;
import javax.microedition.lcdui.Graphics;
import javax.microedition.lcdui.Image;
import javax.microedition.lcdui.Item;
import javax.microedition.lcdui.ItemStateListener;
import javax.microedition.midlet.MIDlet;

public class TestMidlet extends MIDlet implements ItemStateListener {
    class MyButton extends CustomItem {
        private Image _image = null;
        private boolean _down = false;
        private int _clicks = 0;

        public MyButton(Image image) {
            super("");
            _image = image;
        }

        // Button's image
        public void setImage(Image image) {
            _image = image;
            repaint();
        }
        public Image getImage() {
            return _image;
        }

        // Has the button been clicked?
        public boolean isClicked() {
            if(_clicks>0) {
                _clicks -= 1;
                return true;
            }
            return false;
        }

        // Is the button currently down?
        public boolean isDown() {
            return _down;
        }
        public void setDown(boolean down) {
            if(_down)
                _clicks += 1;
            if(down!=_down) {
                _down = down;
                repaint();
                notifyStateChanged();
            }
        }
        public void setDown() {
            setDown(true);
        }
        public void setUp() {
            setDown(false);
        }

        // Minimal button size = image size
        protected int getMinContentHeight() {
            return getImage().getHeight();
        }
        protected int getMinContentWidth() {
            return getImage().getWidth();
        }
        // Preferred button size = image size + borders
        protected int getPrefContentHeight(int width) {
            return getImage().getHeight()+2;
        }
        protected int getPrefContentWidth(int height) {
            return getImage().getWidth()+2;
        }

        // Button painting procedure
        protected void paint(Graphics g, int w, int h) {
            // Fill the button with grey color - background 
            g.setColor(192, 192, 192);
            g.fillRect(0, 0, w, h);
            // Draw the image in the center of the button
            g.drawImage(getImage(), w/2, h/2, Graphics.HCENTER|Graphics.VCENTER);
            // Draw the borders
            g.setColor(isDown()?0x000000:0xffffff);
            g.drawLine(0, 0, w, 0);
            g.drawLine(0, 0, 0, h);
            g.setColor(isDown()?0xffffff:0x000000);
            g.drawLine(0, h-1, w, h-1);
            g.drawLine(w-1, 0, w-1, h);
        }

        // If FIRE key is pressed, the button becomes pressed (down state)
        protected void keyPressed(int c) {
            if(getGameAction(c)==Canvas.FIRE)
                setDown();
        }
        // When FIRE key is released, the button becomes released (up state)
        protected void keyReleased(int c) {
            if(getGameAction(c)==Canvas.FIRE)
                setUp();
        }
        // The same for touchscreens
        protected void pointerPressed(int x, int y) {
            setDown();
        }
        protected void pointerReleased(int x, int y) {
            setUp();
        }
    }

    MyButton button = null;

    public void itemStateChanged(Item item) {
        if(item==button) {
            if(button.isClicked())
                System.out.print("clicked, ");
            System.out.println(button.isDown()?"currently down":"currently up");
        }
    }

    public void startApp() {
        try {
            Form form = new Form("Example");
            button = new MyButton(Image.createImage("/icon.png"));
            form.append(button);
            form.setItemStateListener(this);
            Display.getDisplay(this).setCurrent(form);
        } catch(Exception e) {
            e.printStackTrace();
        }
    }

    public void pauseApp() {
    }

    public void destroyApp(boolean unconditional) {
        notifyDestroyed();
    }
}