splashcanvas.java

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package com.j2medev.chapter3.splash;

import java.io.IOException;
import java.util.Timer;
import java.util.TimerTask;
import javax.microedition.lcdui.*;

public class SplashCanvas extends Canvas {
    
    private Welcome midlet = null;//保存MIDlet的引用方便回调
    private Displayable nextUI = null;
    private Timer timer = new Timer();//使用Timer执行循环绘图的功能
    private int width;
    private int height;
    private int y = 0;//y代表变化的clipY值
    //第一次执行paint()的时候需要执行clearBackground()
    private boolean first = true;
    private Image img = null;
    private Font font = null;
    
    public SplashCanvas(Welcome midlet, Displayable disp) {
        this.midlet = midlet;
        this.nextUI = disp;
        width = this.getWidth();
        height = this.getHeight();
        font = Font.getDefaultFont();
        //初始化图片
        try {
            img = Image.createImage("/logo.png");
        } catch (IOException e) {
            e.printStackTrace();
        }
        //初始化y值
        y=height/2-img.getHeight()/2;
    }
    
    protected void paint(Graphics g) {
        if(first){
            clearBackground(g);
            first = false;
        }
        //设置裁减区域
        g.setClip(0,y, width, 5);
        //绘制图片
        g.drawImage(img, width / 2, height/ 2, Graphics.HCENTER| Graphics.VCENTER);
        //图片绘制完成后就绘画文本
        if(y> (height+img.getHeight())/2){
            g.drawString("与朋友分享图片", width/2, (height+img.getHeight())/2+font.getHeight(), Graphics.HCENTER|Graphics.TOP);
        }
        
    }
    private void clearBackground(Graphics g){
        //清除背景
        int color = g.getColor();
        g.setColor(0xFFFFFF);
        g.fillRect(0,0, width,height);
        g.setColor(color);
    }
    //任意键被按下就跳转到下个UI
    protected void keyPressed(int keyCode) {
        dismiss();
    }
    
    protected void pointerPressed(int y, int x) {
        dismiss();
    }
    //停止timer并进入下个UI
    private void dismiss() {
        timer.cancel();
        midlet.setCurrent(nextUI);
    }
    //在Canvas被显示的时候开始执行TimerTask的内容
    protected void showNotify() {
        timer.schedule(new TimerTask() {
            public void run() {
                repaint();
                //画完图片和文字后就进入下个UI
                if(y > (height + img.getHeight())/ 2+3*font.getHeight()){
                    //休眠500ms
                    try{
                        Thread.sleep(500);
                    }catch(Exception ex){
                        ex.printStackTrace();
                    }
                    dismiss();
                }
                y = y + 5;
            }
        },0,150);
    }
}