现在我们来说说上边的ExpensesTracker里边用到的j2me知识，同时我会介绍polish，通过polish来美化ExpensesTracker。我会从j2me基本的GUI（主要是javax.microedition.lcdui;类）编程，然后会讨论j2me里的数据存储。

ExpensesTracker 程序里边由一个单独的MIDlet(Expenses)和一个数据类(ExpenseInfo)组成。Expenses提供了简单的UI，而ExpenseInfo则定义了数据的结构（fields for data and time, description, amount, and category ）。因为lcdc1.0是不支持floating-point数据的（lcdc1.1支持），所在在ExpenseInfo里用两个独立的int 来记录expense amount的dollars和cents。

基本UI：

从上边工程运行的效果来看，Expenses UI 由一个List 组件（显示了你记录了的Expense条目）和三个Command 组件（quitting the app, editing an item, adding a new item）组成。

List是继承Screen类而来的，在j2me中的List组件其有三种类型：

· Implicit Lists (Expenses里是用此类型) ：允许只能选择一个item, 当你选择某个item时会触发commandAction 事件。

· Exclusive Lists（单选）：以radio按钮形式显示，一次只能选择一个item，选择时不会触发commandAction 事件。

· Multiple Lists（多选）： 以check boxes 按钮形式显示，允许多选，选择时不会触发commandAction事件。

当用户选择之后，可以通过下面的方法返回选定的索引值：

getSelectedIndex()--------返回List中一个选定项的索引值。

Polish工程项目的编译，运行，打包等等，是由build.xml文件控制的。下边是ExpensesTracker工程里的build.xml：

<project
    name="ExpenseTracker"
    default="j2mepolish">
    <!-- extend the default NetBeans build script:           -->
    <import file="nbproject/build-impl.xml"/>
    <!-- import user specific properties                          -->
    <property file="${user.name}.properties" />
    <!-- The polish.home property needs to point to the directory -->
    <!-- containing the J2ME Polish installation.                 -->
    <property name="polish.home" location="C:\Program Files\J2ME-Polish" />
    <!-- import global properties                                 -->
    <property file="${polish.home}/global.properties" />

    <!-- Definition of the J2ME Polish task:                      -->
    <taskdef name="j2mepolish"
        classname="de.enough.polish.ant.PolishTask"
        classpath="${polish.home}/lib/enough-j2mepolish-build.jar:${polish.home}/lib/jdom.jar"
    />
    <!-- build targets, each target can be called via "ant [name]",
         e.g. "ant clean", "ant test j2mepolish" or just "ant" for calling the default-target -->
    <target name="j2mepolish-init"
            depends="init"
        >
          <property name="test" value="false" />
          <property name="customization" value="" />
        <property name="dir.work" value="build/real/${customization}" />
        <property name="dir.dist" value="dist/${customization}" />
        <property name="deploy-url" value="" />
    </target>
    <!-- In this target the J2ME Polish task is used.             -->
    <!-- It has 3 sections:                                       -->
    <!--    1. The info-section defines some general information  -->
    <!--    2. The deviceRequirements-section chooses the devices -->
    <!--       for which the application is optimized.            -->
    <!--    3. The build-section controls the actual build        -->
    <!--       process.                                           -->   
    <target name="j2mepolish"
            depends="j2mepolish-init"
            description="This is the controller for the J2ME build process."
            >
        <j2mepolish>
            <!-- general settings -->
            <info copyright="Copyright 2006, 2007 Your Company. All rights reserved."
                description="Please describe me."
                infoUrl="http://www.j2mepolish.org"
                jarName="${polish.vendor}-${polish.name}-${polish.locale}-ExpenseTracker.jar"
                jarUrl="${deploy-url}${polish.jarName}"
                name="ExpenseTracker"
                vendorName="Enough Software"
                version="1.0.0"
            />
            <!-- selection of supported devices -->
                        <deviceRequirements if="config.active:defined and (test or enableCompilerMode)" >       
                            <requirement name="Identifier" value="${config.active}" />
                        </deviceRequirements>
                        <deviceRequirements if="device:defined and (test or enableCompilerMode)" unless="config.active:defined">
                            <requirement name="Identifier" value="${device}" />
                        </deviceRequirements>
                        <deviceRequirements unless="test or enableCompilerMode">
                            <requirement name="Identifier" value="${devices}" />
                        </deviceRequirements>
            <!-- build settings -->
            <build fullscreen="menu"
                    symbols="polish.skipArgumentCheck"
                    usePolishGui="true"
                    workDir="${dir.work}"
                    destDir="${dir.dist}"
                >
                <!-- midlets definition -->
                <!-- NetBeans defines this property automatically:  -->
                <midlets definition="${manifest.midlets}" if="manifest.midlets:defined" />
                <midlets unless="manifest.midlets:defined">
                    <midlet class="ExpensesApp.Expenses" name="ExpensesTracker" />
                </midlets>
                <!-- project-wide variables - used for preprocessing  -->
                <variables>
                    <!-- Sample configuration options for J2ME Polish
                    <variable name="polish.TextField.useDirectInput" value="true" />
                    <variable name="polish.TextField.supportSymbolsEntry" value="true" />
                    <variable name="polish.MenuBar.useExtendedMenuBar" value="true" />
                    <variable name="polish.useScrollBar" value="true" />
                    -->
                </variables>
                <!-- Configure the customization settings here: -->
                <resources
                    dir="resources/base"
                    defaultexcludes="yes"
                    excludes="readme.txt"
                >
                    <root dir="resources/base/images" />
                    <root dir="resources/base/sounds" />
                    <root dir="resources/${customization}" if="build.${customization}" />
                    <root dir="resources/${customization}/images" if="build.${customization}" />
                    <root dir="resources/${customization}/sounds" if="build.${customization}" />
                    <!-- add the localization element for created localized
                         versions of your application:
                    <localization>
                        <locale name="en_US" />
                        <locale name="de_DE" encoding="utf-8" unless="test" />
                    </localization>
                    -->
                </resources>
                <!-- obfuscator settings: do not obfuscate when the test-property is true -->
                <obfuscator name="ProGuard" unless="test" >
                    <!--
                    You can set additional parameters here, e.g.:
                    <parameter name="optimize" value="false" />
                    -->
                </obfuscator>
                <!-- log settings: only use debug setting when the test-property is true -->
                <debug if="test" showLogOnError="true" verbose="true" level="error">
                    <filter pattern="de.enough.polish.example.*" level="debug" />
                    <filter pattern="de.enough.polish.ui.*" level="warn" />
                    <!-- example for writing log entries to the Recordstore Management System:
                    <handler name="rms" />
                    -->
                </debug>
                <!-- user defined JAD attributes can also be used: -->
                <jad>
                    <attribute name="Nokia-MIDlet-Category" value="Game" if="polish.group.Series40" />
                </jad>   
            </build>
            <!-- execution of emulator(s) -->
            <emulator
                wait="true"
                trace="none"
                securityDomain="trusted"
                enableProfiler="false"
                enableMemoryMonitor="false"
                enableNetworkMonitor="false"
                if="test and not debug"
                >
                <!--
                <parameter name="-Xjam" value="transient=http://localhost:8080/${polish.jadName}" />
                -->
            </emulator>
            <emulator
                wait="true"
                securityDomain="trusted"
                enableProfiler="false"
                enableMemoryMonitor="false"
                enableNetworkMonitor="false"
                if="debug"
                >
                <!-- Attach the emulator to the NetBeans debugger:    -->
                <debugger name="antcall" target="connect-debugger" port="6001" />
            </emulator>
        </j2mepolish>
    </target>
    <target name="setdeploy"
        description="Call this target first to set the OTA download-URL, e.g. ant setdeploy j2mepolish"
        >
        <property name="deploy-url" value="http://www.company.com/download/" />
    </target>
    <target name="enableDebug"
        description="Call this target first to skip the obfuscation step, call the emulator and start the debugger, e.g. ant enableDebug j2mepolish"
        >
        <property name="debug" value="true" />
    </target>
    <target name="enableEmulator"
        description="Call this target first to skip the obfuscation step and call the emulator, e.g. ant test j2mepolish"
        >
        <property name="test" value="true" />
        <property name="dir.work" value="build/test" />
    </target>
    <target
        name="emulator"
        depends="enableEmulator,j2mepolish"
        description="invokes the emulator"
    >
    </target>

    <target name="clean"
              description="allows a clean build. You should call [ant clean] whenever you made changes to devices.xml, vendors.xml or groups.xml">
        <delete dir="build" />
        <delete dir="dist" includes="**/*" />
    </target>

    <target 
        name="cleanbuild"
        description="allows a clean build. You should call [ant cleanbuild] whenever you made changes to devices.xml, vendors.xml or groups.xml"
        depends="clean, j2mepolish"
    />
    <target name="debug" description="debugs the project" depends="enableDebug, enableEmulator, j2mepolish" />
    <target name="deploy"
            description="Deploys the applications. Currently empty."
            depends="j2mepolish"
    />

    <!-- NetBeans specific build targets: -->
            <target name="run"
                    depends="enableEmulator, j2mepolish"
            >
            </target>

            <target name="rebuild"
                    depends="clean, j2mepolish"
            >
            </target>

            <target name="rebuild-all"
                    depends="clean, j2mepolish"
            >
            </target>
            <target name="jar"
                    depends="j2mepolish"
            >
            </target>

            <target name="jar-all"
                    depends="j2mepolish"
            >
            </target>

            <target name="clean-all"
                    depends="clean"
            >
            </target>
            <target name="deploy-all"
                    depends="deploy"
            >
            </target>
            <target name="enable-compiler-mode">
                <property name="enableCompilerMode" value="true" />
            </target>

            <target name="compile-single"
                    depends="enable-compiler-mode, j2mepolish"
            >
            </target>
        <target name="connect-debugger">
            <property name="jpda.port" value="${polish.debug.port}" />
            <antcall target="nbdebug"/>
        </target>

    <target name="enableCustomization1">
        <property name="dir.work" value="build/customization1" />
        <property name="cfg.customization1" value="true" />
    </target>
    <target name="customization1"
            description="customizes this project with the settings found in resources/customization1"
            depends="enableCustomization1, j2mepolish"
    />
    <target name="enableCustomization2">
        <property name="dir.work" value="build/customization2" />
        <property name="cfg.customization2" value="true" />
    </target>
    <target name="customization2"
            description="customizes this project with the settings found in resources/customization2"
            depends="enableCustomization2, j2mepolish"
    />
</project>

build.xml文件中最主要的是<info>，<deviceRequirements>和<build>三部分。

其中<info>元素指定说明了工程中的一般信息，如，工程名和版本。<deviceRequirements>元素是用来指定程序编译时所选择的模拟器。<build>元素是工程编译构件时的主要控制器（如，可以设定属性 usePolishGui=”true”来指定把polish应用当前工程中，而设为false时，则说明当前工程不引入polish，此时工程与一般的mobile应用程序一样）。

当build.xml文件中的<build>属性usePolishGui=”true”时，我们就可以修改工程目录中resources里的polish.css文件控制程序的显示(美化j2me介面)。在j2me程序中只需要以“//#style”指令就可以调用相应的css属性(请注意这指令与注释“//”的区别)。 其中，polish.css文件包含对应用程序的全部items和screens的style定义。

polish.css文件中常用的预定义的style（用于程序中的所有items和screens，但当引用自定义style时，预定义的style会被自定义style覆盖掉：

colors{}：用来定义一系列的颜色，供其它style中的color属性引用。

backgrounds{}：用来定义一系列的背景，供其它style中的background属性引用。

borders{}：用来定义一系列的边框，供其它style中的border属性引用。

focused{}：当获取某个item或screen的焦点时的style。

title{}：应用于所以screen中的title的style。

scrollbar{}：当build.xml文件中“polish.useScrollBar“变量设为true时被scrollbar引用。

label{}：应用于所以item或menu中标签的style。

以下style是当build.xml文件中“polish.MenuBar.useExtendMenuBar“变量设为true时被引用的：

menubar{}， menu{}，menuItem{}，leftcommand{}，rightcommand{}

polish.css文件中自定义style：

注意：styel可以继承的，且引用子style时既保留父style的属性又有自己的属性，同时子style可以重写父style属性。

自定义style名称：如“.mystyle{}”是由点加字符串。注意不能是与预定义的名称相同。

下面我们来对ExpensesTracker中的UI---List以CSS进行修改。

修改后程序运行如下：

其polish.css文件：

colors {
    fontColor: rgb( 30, 85, 86 );
    focusedFontColor: #000;
    bgColor:  #eee;
    focusedBgColor:  #fff;
    borderColor: fontColor;
    focusedBorderColor: focusedFontColor;   
}

focused {
    margin: 1;   
    margin: 3;    
    background {
        type: round-rect;
        arc: 4;
        color: focusedBgColor;
        border-color: focusedBorderColor;
        border-width: 2;
    }
    font {
        style: bold;
        color: focusedFontColor;
        size: small;
    }
    layout: expand;   
}

/**
  * The title style is a predefined style which is used
  * for all screen-titles.
  */
title {
    padding: 2;
    font-face: proportional;
    font-size: large;
    font-style: bold;
    font-color: focusedFontColor;
    border: none;
        background {
            type: vertical-gradient;
            top-color: #fff;
            bottom-color: rgb(140,206,220);
            start: 10%;
            end: 90%;
        }
       layout: expand|center;
}
.expenseList{
    background {
       image:url(BG.png);
       color: rgb(184,235,246)
     }
}
.expenseItem{
        margin: 3;
        padding-left: 3;
        font-face: proportional;
    font-size: small;
    font-style: bold;
    font-color: focusedFontColor;
        focused-style: expenseItemFocused;
}
.expenseItemFocused extends .expenseItem{
        background-color: argb( 150, 255, 255, 255 );
        after: url(listItem.png);
        layout:expand;
}

而Expenses.java中引用CSS的地方(绿色字体)：

public Expenses() {
        display = Display.getDisplay(this);
        //get some play data
        expenseItems = ExpenseInfo.LoadExpenses();
        itemCount = expenseItems.size();
        //Setup the UI
       //#style expenseList
        lsMain = new List("Expenses", List.IMPLICIT) ;
        cmAdd = new Command("New", Command.SCREEN, 3);
        cmEdit = new Command("Edit", Command.ITEM, 2);
        cmExit = new Command("Exit", Command.EXIT, 1);
        lsMain.addCommand(cmAdd);
        lsMain.addCommand(cmEdit);
        lsMain.addCommand(cmExit);

        lsMain.setCommandListener(this);
        //add all the Expense items to lsMain
        rebuildList();
    }

private void rebuildList(){
        //add all the expense items to lsMain
        for(int i=0; i<expenseItems.size(); i++){
            if (expenseItems.elementAt(i) != null){
                ExpenseInfo exp = (ExpenseInfo) expenseItems.elementAt(i);
                //#style expenseItem
                lsMain.append(exp.getDescription(),null);
            }
        }
    }