3.6.2   ImageItem 下面我们来看ImageItem,ImageItem和StringItem其实区别仅仅在于一个是显示图像，一个是文字，它同样有两个构造函数，其中用到最多的是5个参数的构造函数，第一个是该Item的Label,第二个是图片，第三个是等效线，第四个是取代的文字（图片无法现实时），第五个是外观（和StringItem相同）。   import javax.microedition.lcdui.*; import javax.microedition.midlet.*; public class ImageItemMIDlet extends MIDlet implements ItemCommandListener {         private Display display;         public ImageItemMIDlet()         {                 display = Display.getDisplay(this);         }         public void startApp()         {                 Image img = null ;                 try                {                        img = Image.createImage("/pic.png") ;                }catch(Exception e){}                   Form f = new Form("ImageItem测试") ;                 f.append(img) ;                 ImageItem ii1 =                  new ImageItem("图片1",img, Item.LAYOUT_CENTER|Item.LAYOUT_NEWLINE_BEFORE,"图片1取代文字",Item.BUTTON);                 f.append(ii1) ;                 ImageItem ii2 =                  new ImageItem("图片2",img, Item.LAYOUT_RIGHT|Item.LAYOUT_NEWLINE_BEFORE,"图片2取代文字",Item.HYPERLINK);                 f.append(ii2) ;                   display.setCurrent(f);         }         public void commandAction(Command c,Item i)         {                 System.out.println(c.getLabel());                 System.out.println(i.getLabel());         }         public void pauseApp()         {         }         public void destroyApp(boolean unconditional)         {         } }   3.7    CustomItem CustomItem是Item中一个比较重要的子类，它最大的优点是提高了Form中的可交互性。它和Canvas有很大的相似处。我们通过改写CustomItem可以实现完全控制在新的子类中条目区域的显示，它可以定义使用的颜色，字体和图形，包括特殊高亮的条目可能有的所有的焦点状态，只有条目的Label是有系统控制生成的，但是Label总是生成在CustomItem的内容区域外。   每个CustomItem都负责把它的行为与目标设备上可用的交互模式匹配。一个CustomItem调用方法来观察特定设备所支持的交互模式，这个方法会返回一个支持模式的位标记，支持的模式会的返回对应位会被设置，不支持的不被设置。   CustomItem一个比较重要的特性即是Form内部的遍历，即实现可能临时把遍历的责任委派给Item本身，这样可以实现特殊的高亮，动画等等效果。   由于customItem在Form类里扮演很重要的角色，其内容很庞杂，我们通过三个代码段来教读者如何使用CustomItem,希望大家通过对代码的深刻认识，提高自己对CustomItem的掌握程度。   import javax.microedition.lcdui.*; import javax.microedition.midlet.MIDlet;     public class CustomItemDemo extends MIDlet implements CommandListener {     private final static Command CMD_EXIT = new Command("Exit", Command.EXIT, 1);     private Display display;         private boolean firstTime;     private Form mainForm;         public CustomItemDemo() {         firstTime = true;         mainForm = new Form("Custom Item");     }       protected void startApp() {         if(firstTime) {             display = Display.getDisplay(this);               mainForm.append(new TextField("Upper Item", null, 10, 0));             mainForm.append(new Table("Table", Display.getDisplay(this)));             mainForm.append(new TextField("Lower Item", null, 10, 0));             mainForm.addCommand(CMD_EXIT);             mainForm.setCommandListener(this);             firstTime = false;         }         display.setCurrent(mainForm);     }       public void commandAction(Command c, Displayable d) {         if (c == CMD_EXIT) {             destroyApp(false);             notifyDestroyed();         }     }       protected void destroyApp(boolean unconditional) {     }       protected void pauseApp() {     } }   import javax.microedition.lcdui.*; public class Table     extends CustomItem     implements ItemCommandListener {       private final static Command CMD_EDIT = new Command("Edit",                                                            Command.ITEM, 1);     private Display display;     private int rows = 5;     private int cols = 3;     private int dx = 50;     private int dy = 20;     private final static int UPPER = 0;     private final static int IN = 1;     private final static int LOWER = 2;     private int location = UPPER;     private int currentX = 0;     private int currentY = 0;     private String[][] data = new String[rows][cols];         // Traversal stuff         //indicating support of horizontal traversal internal to the CustomItem     boolean horz;         //indicating support for vertical traversal internal to the CustomItem.     boolean vert;       public Table(String title, Display d) {         super(title);         display = d;         setDefaultCommand(CMD_EDIT);         setItemCommandListener(this);         int interactionMode = getInteractionModes();         horz = ((interactionMode & CustomItem.TRAVERSE_HORIZONTAL) != 0);         vert = ((interactionMode & CustomItem.TRAVERSE_VERTICAL) != 0);     }       protected int getMinContentHeight() {           return (rows * dy) + 1;     }       protected int getMinContentWidth() {           return (cols * dx) + 1;     }       protected int getPrefContentHeight(int width) {           return (rows * dy) + 1;     }       protected int getPrefContentWidth(int height) {           return (cols * dx) + 1;     }       protected void paint(Graphics g, int w, int h) {           for (int i = 0; i <= rows; i++) {             g.drawLine(0, i * dy, cols * dx, i * dy);         }           for (int i = 0; i <= cols; i++) {             g.drawLine(i * dx, 0, i * dx, rows * dy);         }           int oldColor = g.getColor();         g.setColor(0x00D0D0D0);         g.fillRect((currentX * dx) + 1, (currentY * dy) + 1, dx - 1, dy - 1);         g.setColor(oldColor);           for (int i = 0; i < rows; i++) {               for (int j = 0; j < cols; j++) {                   if (data[i][j] != null) {                       // store clipping properties                     int oldClipX = g.getClipX();                     int oldClipY = g.getClipY();                     int oldClipWidth = g.getClipWidth();                     int oldClipHeight = g.getClipHeight();                     g.setClip((j * dx) + 1, i * dy, dx - 1, dy - 1);                     g.drawString(data[i][j], (j * dx) + 2, ((i + 1) * dy) - 2,                                  Graphics.BOTTOM | Graphics.LEFT);                       // restore clipping properties                     g.setClip(oldClipX, oldClipY, oldClipWidth, oldClipHeight);                 }             }         }     }       protected boolean traverse(int dir, int viewportWidth, int viewportHeight,                                int[] visRect_inout) {                                                 if (horz && vert) {                                                switch (dir) {                     case Canvas.DOWN:                         if (location == UPPER) {                         location = IN;                     } else {                             if (currentY < (rows - 1)) {                             currentY++;                             repaint(currentX * dx, (currentY - 1) * dy, dx, dy);                             repaint(currentX * dx, currentY * dy, dx, dy);                         } else {                             location = LOWER;                                 return false;                         }                     }                         break;                     case Canvas.UP:                         if (location == LOWER) {                         location = IN;                     } else {                             if (currentY > 0) {                             currentY--;                             repaint(currentX * dx, (currentY + 1) * dy, dx, dy);                             repaint(currentX * dx, currentY * dy, dx, dy);                         } else {                             location = UPPER;                                 return false;                         }                     }                         break;                     case Canvas.LEFT:                         if (currentX > 0) {                         currentX--;                         repaint((currentX + 1) * dx, currentY * dy, dx, dy);                         repaint(currentX * dx, currentY * dy, dx, dy);                     }                         break;                     case Canvas.RIGHT:                         if (currentX < (cols - 1)) {                         currentX++;                         repaint((currentX - 1) * dx, currentY * dy, dx, dy);                         repaint(currentX * dx, currentY * dy, dx, dy);                     }             }         } else if (horz || vert) {             switch (dir) {                          case Canvas.UP:                 case Canvas.LEFT:                                         if (location == LOWER) {                         location = IN;                     } else {                             if (currentX > 0) {                             currentX--;                             repaint((currentX + 1) * dx, currentY * dy, dx, dy);                             repaint(currentX * dx, currentY * dy, dx, dy);                         } else if (currentY > 0) {                             currentY--;                             repaint(currentX * dx, (currentY + 1) * dy, dx, dy);                             currentX = cols - 1;                             repaint(currentX * dx, currentY * dy, dx, dy);                         } else {                             location = UPPER;                             return false;                         }                     }                         break;                     case Canvas.DOWN:                 case Canvas.RIGHT:                     if (location == UPPER) {                         location = IN;                     } else {                             if (currentX < (cols - 1)) {                             currentX++;                             repaint((currentX - 1) * dx, currentY * dy, dx, dy);                             repaint(currentX * dx, currentY * dy, dx, dy);                         } else if (currentY < (rows - 1)) {                             currentY++;                                                 repaint(currentX * dx, (currentY - 1) * dy, dx, dy);                             currentX = 0;                             repaint(currentX * dx, currentY * dy, dx, dy);                         } else {                             location = LOWER;                             return false;                         }                     }                                     }         } else {             //In case of no Traversal at all: (horz|vert) == 0         }           visRect_inout[0] = currentX;         visRect_inout[1] = currentY;         visRect_inout[2] = dx;         visRect_inout[3] = dy;           return true;     }       public void setText(String text) {         data[currentY][currentX] = text;         repaint(currentY * dx, currentX * dy, dx, dy);     }       public void commandAction(Command c, Item i) {           if (c == CMD_EDIT) {               TextInput textInput = new TextInput(data[currentY][currentX], this,                                                 display);             display.setCurrent(textInput);         }     } }     import javax.microedition.lcdui.*; import javax.microedition.midlet.MIDlet;     public class TextInput extends TextBox implements CommandListener {       private final static Command CMD_OK = new Command("OK", Command.OK,                                                            1);            private final static Command CMD_CANCEL = new Command("Cancel", Command.CANCEL,                                                         1);          private Table parent;     private Display display;       public TextInput(String text, Table parent, Display display) {         super("Enter Text", text, 50, TextField.ANY);         this.parent = parent;         this.display = display;         addCommand(CMD_OK);         addCommand(CMD_CANCEL);         setCommandListener(this);     }       public void commandAction(Command c, Displayable d) {         if (c == CMD_OK) {             // update the table's cell and return             parent.setText(getString());             display.setCurrentItem(parent);         } else if (c == CMD_CANCEL) {             // return without updating the table's cell             display.setCurrentItem(parent);         }     }     } 3.8    TextField和DateField TextField和我们前面讲的TextBox大同小异，只是它是作为Form的一个子类存在，而TextBox则是和Form平起平坐，因此我们直接给出代码方便大家的学习。   import javax.microedition.lcdui.*; import javax.microedition.midlet.*; public class TextFieldWithItemStateListenerMIDlet extends MIDlet implements ItemStateListener {         private Display display;         public TextFieldWithItemStateListenerMIDlet()         {                 display = Display.getDisplay(this);         }         TextField name ;         TextField tel ;         TextField summary ;         public void startApp()         {                 Form f = new Form("TextField测试") ;                   name = new TextField("姓名","",8,TextField.ANY) ;                 tel = new TextField("电话","",14,TextField.PHONENUMBER) ;                 summary = new TextField("总结","",30,TextField.UNEDITABLE) ;                   f.append(name) ;                 f.append(tel) ;                 f.append(summary) ;                 f.setItemStateListener(this);                 display.setCurrent(f);         }         public void itemStateChanged(Item item)         {                 if(item==name)                 {                         summary.setString("输入的姓名为："+name.getString());                 }else if(item==tel)                 {                         summary.setString("输入的电话为："+tel.getString());                 }else                 {                        summary.setString("");                 }         }         public void pauseApp()         {         }         public void destroyApp(boolean unconditional)         {         } }   DateField的目的是方便用户输入时间，它的构造函数共有三个参数，一个是Label，一个是输入模式，一个是java.util.TimeZone对象，也可以省去第三个参数，只使用前两个。 3.9    Gauge和Spacer,ChoiceGroup 3.9.1   Gauge Alert有一套方法可以显示进度，利用setIndicator()/getIndicator()这组函数，可以显示进度的画面。Gauge的最大用处就是拿来当进度显示使用。     拿来当进度显示用的Gauge对象必须满足如下要求： l         控制与用户交互的构造函数的第二个参数必须为flase l         不能被其他的Form或者Alert使用 l         不能加入Command l         不能有Label l         不能自己设定等效线的位置。 l         不能自己设定组件的大小。   大家可以参考如下的代码： import javax.microedition.lcdui.*; import javax.microedition.midlet.*; public class AlertWithIndicatorMIDlet extends MIDlet implements CommandListener {         private Display display;         public AlertWithIndicatorMIDlet()         {                 display = Display.getDisplay(this);         }         Gauge g ;         public void startApp()         {                 Alert al = new Alert("处理中");                 al.setType(AlertType.INFO);                 al.setTimeout(Alert.FOREVER);                 al.setString("系统正在处理中");                   g = new Gauge(null,false,10,0) ;                 al.setIndicator(g);                   Command start = new Command("开始",Command.OK,1) ;                 Command stop = new Command("停止",Command.STOP,1) ;                 al.addCommand(start);                 al.addCommand(stop);                 al.setCommandListener(this);                 display.setCurrent(al);         }         public void commandAction(Command c,Displayable s)         {                 String cmd = c.getLabel() ;                 if(cmd.equals("开始"))                 {                         for(int i=0 ; i <11 ; i++)                         {                                 g.setValue(i);                                 try                                 {                                         Thread.sleep(500);                                 }catch(Exception e){}                         }                 }else if(cmd.equals("停止"))                 {                         notifyDestroyed() ;                 }         }         public void pauseApp()         {         }         public void destroyApp(boolean unconditional)         {         } }   3.9.2   Spacer Spacer的用处很简单，就是加一处空白，大家可以参考API文档进行实际开发。   3.9.3   ChoiceGroup ChoiceGroup和List大同小异，因为二者都实现了Choice接口，所以在很多地方是一样的，但是请注意一点，在这里我们不能使用Choice.IMPLICIT类型，只能用Choice.EXCLUSIVE,Choice.MUTIPLE,Choice.POPUP,三种类型，与List的区别即第三种弹出式菜单。

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