两个Canvas切换的问题

最新推荐文章于 2022-05-09 16:43:38 发布

lq547854

最新推荐文章于 2022-05-09 16:43:38 发布

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本文链接：https://blog.youkuaiyun.com/lq547854/article/details/5915929

本文介绍如何在Java ME应用中实现不同屏幕间的切换，通过Midlet类管理Canvas对象，并利用CommandListener接口响应用户操作，完成从一个Canvas到另一个Canvas的跳转。

在一个midlet中setCurrent()了一个Canvas类的对象c1，然后在c1中的keyPressed()的case FIRE:中想将屏幕转换到另外一个Canvas类的对象c2,该怎么写,具体原理哈,别光说setCurrent.如果回调midlet中的方法的话,在Canvas类中怎么标记midlet
我是菜鸟别见怪哈

public MyMIDlet extends MIDlet{

public static Display display;
public MyMIDlet(){
display = Display.getDisplay(this);

}

}

在界面c1中，使用如下代码切换：
MyMIDlet.display.setCurrent(new C2());

package prj1_1_2;

import javax.microedition.lcdui.Display;
import javax.microedition.midlet.MIDlet;
import javax.microedition.midlet.MIDletStateChangeException;

public class Midlet1 extends MIDlet {
    private FirstCanvas fcan;
    public static Display display;
    public Midlet1() {
        super();
        fcan=new FirstCanvas();
        display=Display.getDisplay(this);
    }

    protected void destroyApp(boolean arg0) throws MIDletStateChangeException {

    }

    protected void pauseApp() {


    }

    protected void startApp() throws MIDletStateChangeException {
        display.setCurrent(fcan);

    }

}
package prj1_1_2;

import javax.microedition.lcdui.Canvas;
import javax.microedition.lcdui.Command;
import javax.microedition.lcdui.CommandListener;
import javax.microedition.lcdui.Displayable;
import javax.microedition.lcdui.Graphics;

public class FirstCanvas extends Canvas implements CommandListener{
    private Command cmdSecond=new Command("第二屏",Command.SCREEN,1);
    public FirstCanvas() {
        super();
        this.addCommand(cmdSecond);
        this.setCommandListener(this);
    }

    protected void paint(Graphics g) {
        g.setColor(127, 0, 0);
        g.fillRect(0, 0, this.getWidth(), this.getHeight());
        g.setColor(0, 127, 0);
        g.drawString("FirstCanvas", 0, 0, Graphics.TOP|Graphics.LEFT);

    }

    public void commandAction(Command c, Displayable d) {
        if(c==cmdSecond){
            System.out.println("第二屏");
            Midlet1.display.setCurrent(new SecondCanvas());
        }

    }

}
package prj1_1_2;

import javax.microedition.lcdui.Canvas;
import javax.microedition.lcdui.Graphics;

public class SecondCanvas extends Canvas{

    public SecondCanvas() {
        super();
    }

    protected void paint(Graphics g) {
        g.setColor(0, 127, 0);
        g.fillRect(0, 0, this.getWidth(), this.getHeight());
        g.setColor(0, 0, 127);
        g.drawString("SecondCanvas", 0, 0, Graphics.TOP|Graphics.LEFT);

    }

}
先将所有的Canvas在Midlet中建立构造函数并初始化，你需要在某个Canvas中调用另外的Canvas时就只需要注意以下两点：
1、在Canvas中引入Midlet
eg:private shixunMIDlet midlet;
2、直接调用即可
eg:其中的showScnNew()都是Canvas在Midlet中建立的函数名
if(inMenu){
switch(curSel)
{
case 1:
midlet.showScnNew();
break;
case 2:
break;
case 3:
midlet.showScnHelp();
break;
case 4:
midlet.showScnAbout();
break;
case 5:
try {
midlet.destroyApp(true);
} catch (MIDletStateChangeException e) {
// TODO 自动生成 catch 块
e.printStackTrace();
}
break;
}