ImageItem对象是一个项目类型的对象,他的作用是在容器中显示图片。那么如何使用ImageItem对象呢?请按照下面三个步骤进行:
1.构造一个Image对象,相关代码如下所示:
Image img=Image.createImage("/fancy/test/JavaPowered-8.png");
createImage()方法是Image类的静态方法,它的作用是根据图形文件创建一个Image对象。
J2ME程序中所用到的图片文件必须存放在apps\fancy\res文件夹下面。
2.构造ImageItem对象,相关代码如下所示:
imgItem=new ImageItem("Default Layout",img,ImageItem.LAYOUT_DEFAULT,
"Image Cannot be shown");


ImageItem类的构造函数有三个参数,第一个参数的作用是显示一个标签,第二个参数指明图片的对齐方式,第三个参数的作用是显示图片的tip。
3.利用容器类对象的append()方法将ImageItem对象添加进去。如:
props.append(imgItem);
下面我们来看一个比较完整的例子。
package fancy.test;

import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;

public class ShowImageItem extends MIDlet implements CommandListener
{
private Display display;
private Form props;
private Image img;
private ImageItem imgItem;

private Command exitCommand = new Command("Exit", Command.EXIT, 1);

public ShowImageItem()


{
display = Display.getDisplay(this);
}

public void startApp()
{
props = new Form("Hello World");
//props.append("Hello World!\n");
try
{
img=Image.createImage("/fancy/test/JavaPowered-8.png");
imgItem=new ImageItem("Default Layout",
img,ImageItem.LAYOUT_DEFAULT,"Image Cannot be
shown");
props.append(imgItem);
props.append(new ImageItem("Left Layout",
img,ImageItem.LAYOUT_LEFT,"Image Cannot be
shown"));
props.append(new ImageItem("Center Layout",
img,ImageItem.LAYOUT_CENTER,"Image Cannot be
shown"));
}


catch(Exception fe)
{
//to do nothing
}

props.addCommand(exitCommand);
props.setCommandListener(this);
display.setCurrent(props);
}

public void commandAction(Command c, Displayable s)
{
if (c == exitCommand)
{
destroyApp(false);
notifyDestroyed();
}
}

public void destroyApp(boolean unconditional)
{
}



public void pauseApp()
{
display.setCurrent(null);
props = null;
}

}
ShowImageItem.java程序的运行效果如下图所示:

ChoiceGroup也是一个项目类型的对象,它代表一个选择列表,它的作用和List对象类似,不过后者是一个容器,而前者是一个项目。
我们需要特别注意ChoiceGroup类的构造函数,它有四个参数,第一个参数是标签,第二个参数是此选择列表的类型,例如多选还是单选。第三个参数是一个字符串数组,代表每个选项的标签,第四个选项是一个Image类型的数组,代表每个选项前面的小图标。下面是一个比较完整的例子。
package fancy.test;

import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;

public class ShowChoiceGroup extends MIDlet implements CommandListener

{
private Display display;
private Form props;


private Image duke;
private Image[] imageArray;
private ChoiceGroup choice;

private Command exitCommand = new Command("Exit", Command.EXIT, 1);

public ShowChoiceGroup()
{
display = Display.getDisplay(this);
}

public void startApp()
{
props = new Form("Hello World");
//props.append("Hello World!\n");
try
{
Image duke= Image.createImage("/fancy/test/Icon.png");
imageArray = new Image[]{duke,duke,duke};
String[] stringArray = { "Option A", "Option B",
"Option C" };
choice=new ChoiceGroup("choice group",


ChoiceGroup.MULTIPLE,stringArray,imageArray);
props.append(choice);
}
catch(Exception fe)
{
//to do nothing.
}
props.addCommand(exitCommand);
props.setCommandListener(this);
display.setCurrent(props);
}

public void commandAction(Command c, Displayable s)
{
if (c == exitCommand)
{
destroyApp(false);
notifyDestroyed();
}


public void destroyApp(boolean unconditional)


{
}

public void pauseApp()
{
display.setCurrent(null);
props = null;
}
}
ShowChoiceGroup.java程序的运行效果如下图所示:


Gauge对象是一个项目类型的对象,它的作用是显示一个进度条。请看下面的源代码。
Gauge类的构造函数的后面两个参数分别是进度条的最大值和初始值。
package fancy.test;

import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;

public class ShowGauge extends MIDlet implements CommandListener
{
private Display display;
private Form props;

private Command exitCommand = new Command("Exit", Command.EXIT, 1);

public ShowGauge()
{
display = Display.getDisplay(this);
}

public void startApp()
{


props = new Form("Hello World");
//props.append("Hello World!\n");
Gauge gauge=new Gauge("show gauge",true,100,50);
props.append(gauge);
props.addCommand(exitCommand);
props.setCommandListener(this);
display.setCurrent(props);
}

public void commandAction(Command c, Displayable s)
{
if (c == exitCommand)
{
destroyApp(false);
notifyDestroyed();
}
}

public void destroyApp(boolean unconditional)
{
}



public void pauseApp()
{
display.setCurrent(null);
props = null;
}

}
Ticker对象是一个项目类型的对象,它的作用相当于一个滚动消息栏,在屏幕的上方显示滚动的信息。 Ticker类的构造函数仅有一个参数,那就是需要滚动显示的消息。
package fancy.test;

import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;

public class ShowTicker extends MIDlet implements CommandListener
{
private Display display;
private Form props;


private Command exitCommand = new Command("Exit", Command.EXIT, 1);

public ShowTicker()
{
display = Display.getDisplay(this);
}

public void startApp()
{
props = new Form("Hello World");


props.append("Hello World!\n");
Ticker ticker=new Ticker("D??￥ò?ò1
;ìy′oóê");
props.setTicker(ticker);
props.addCommand(exitCommand);
props.setCommandListener(this);
display.setCurrent(props);
}

public void commandAction(Command c, Displayable s)

{
if (c == exitCommand)
{
destroyApp(false);
notifyDestroyed();
}
}

public void destroyApp(boolean unconditional)
{
}



public void pauseApp()
{
display.setCurrent(null);
props = null;
}

}
ShowTicker.java程序的运行效果如下图所示:


在前面的例子中,我们已经演示了如何构造J2ME程序的用户界面。现在有一个问题,那就是如何与用户界面交互呢?亦即如何获取用户通过用户界面输入的值呢?请看下面的例子。
package fancy.test;

import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;

public class GetTextBoxValue extends MIDlet implements CommandListener

{
private Display display;
private TextBox txtBox;

private Command exitCommand = new Command("Exit", Command.EXIT, 1);
private Command getCommand = new Command("GETVALUE", Command.OK, 1);

public GetTextBoxValue()
{
display = Display.getDisplay(this);
}



public void startApp()
{
//or :
//String str="hello world";
//txtBox = new TextBox("Text Box",str,str.length(),0);
//the follow code is wrong:
//txtBox = new TextBox("Text Box",str,any number here,0);

txtBox = new TextBox("Text Box",null,200,0);

txtBox.addCommand(exitCommand);
txtBox.addCommand(getCommand);
txtBox.setCommandListener(this);
display.setCurrent(txtBox);
}

public void valueScreen()
{
Form props=new Form("get text box value");
props.append(txtBox.getString());
props.addCommand(exitCommand);
props.setCommandListener(this);


display.setCurrent(props);
}

public void commandAction(Command c, Displayable s)
{
if (c == exitCommand)
{
destroyApp(false);
notifyDestroyed();
}
if(c==getCommand)
{
valueScreen();
}
}

public void destroyApp(boolean unconditional)
{
}

public void pauseApp()
{


display.setCurrent(null);
txtBox = null;
}

}
在上面的例子中(GetTextBoxValue.java),当我们往文本框中输入文本,并按下退出按钮,接着选择GETVALUE命令的时候,将会调用valueScreen()方法。valueScreen()方法的源代码如下
:
public void valueScreen()
{
Form props=new Form("get text box value");
props.append(txtBox.getString());
props.addCommand(exitCommand);
props.setCommandListener(this);
display.setCurrent(props);
}
valueScreen()方法的逻辑是:首先创建一个容器对象Form,然后调用TextBox对象的getString()方法,获取文本框中的输入值,追加到容器对象中,最后将此Form对象作为屏幕的当前显示对象。GetTextBoxValue.java的运行效果如下面两图所示:

Date对象是属于java.util包的,它的作用是返回当前的时间。请看下面的代码:

package fancy.test;

import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;


import java.util.*;

public class GetDate extends MIDlet implements CommandListener
{
private Display display;
private Form props;
private Date date;

private Command exitCommand = new Command("Exit", Command.EXIT, 1);

public GetDate()
{
display = Display.getDisplay(this);
}

public void startApp()
{
props = new Form("Hello World");
props.append("Hello World!\n");
date=new Date();
props.append("Now Time:"+date.getTime()+"\n");



props.addCommand(exitCommand);
props.setCommandListener(this);
display.setCurrent(props);
}

public void commandAction(Command c, Displayable s)
{
if (c == exitCommand)
{
destroyApp(false);
notifyDestroyed();
}
}

public void destroyApp(boolean unconditional)
{
}

public void pauseApp()
{
display.setCurrent(null);
props = null;


}

}
GetDate.java程序的运行效果如下图所示:


TimeZone对象也是属于java.util包的。这个对象的作用是提供关于时区的信息。TimeZone类有一个静态方法----getDefault(),可以获取与当前系统相关的时区对象。getAvailableIDs()方法可以获取系统中所有可用的时区的ID号,getID()方法可以获取系统当前所设置的时
区。具体的例子如下所示:
package fancy.test;

import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
import java.util.*;

public class GetTimeZone extends MIDlet implements CommandListener
{
private Display display;
private Form props;
//private Date date;
private TimeZone zone;

private Command exitCommand = new Command("Exit", Command.EXIT, 1);

public GetTimeZone()
{
display = Display.getDisplay(this);
}



public void startApp()
{
props = new Form("Hello World");
props.append("Hello World!\n");
//date=new Date();
//props.append("Now Time:"+date.getTime()+"\n");
zone=TimeZone.getDefault();
String []zoneid=zone.getAvailableIDs();
for(int i=0;i<zoneid.length;i++)
{
props.append(zoneid[i]+"\n");
}
props.append("Current Time Zone:"+zone.getID()+"\n");
props.addCommand(exitCommand);
props.setCommandListener(this);
display.setCurrent(props);
}

public void commandAction(Command c, Displayable s)
{
if (c == exitCommand)
{


destroyApp(false);
notifyDestroyed();
}
}


public void destroyApp(boolean unconditional)
{
}

public void pauseApp()
{
display.setCurrent(null);
props = null;
}

}


Calendar对象归属于java.util包,它可以提供更为详尽的时间信息。具体的例子如下所示:
package fancy.test;

import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
import java.util.*;

public class GetCalendar extends MIDlet implements CommandListener
{
private Display display;
private Form props;
//private Date date;


//private TimeZone zone;
//private Calendar calendar;

private Command exitCommand = new Command("Exit", Command.EXIT, 1);

public GetCalendar()
{
display = Display.getDisplay(this);
}

public void startApp()
{
props = new Form("Hello World");
props.append("Hello World!\n");

Calendar rightNow = Calendar.getInstance();
props.append("YEAR:"+rightNow.get(Calendar.YEAR)+"\n");
props.append("MONTH:"+rightNow.get(Calendar.MONTH)+"\n");
props.append("DAY OF MONTH:"
+rightNow.get(Calendar.DAY_OF_MONTH)+"\n");
props.append("HOUR OF DAY:"
+rightNow.get(Calendar.HOUR_OF_DAY)+"\n");


props.append("MINUTE:"
+rightNow.get(Calendar.MINUTE)+"\n");
props.append("SECOND:"
+rightNow.get(Calendar.SECOND)+"\n");
props.append("MILLISECOND:"
+rightNow.get(Calendar.MILLISECOND)+"\n");

//date=new Date();
//props.append("Now Time:"+date.getTime()+"\n");
//zone=TimeZone.getDefault();
//String []zoneid=zone.getAvailableIDs();
//for(int i=0;i<zoneid.length;i++)
//{
// props.append(zoneid[i]+"\n");
/

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