我想弄清楚，在 Canvas 的 commandAction 方法中，如何让我的命令按钮带我回到 MIDlet 的开头？（基本上重新开始）。
当钥匙触发时，我让它带我到一个新的列表页面。在那个页面上，我有一个后退按钮，理想情况下我需要它来带我回到 CalandarMidlet 页面。我的逻辑是，在 commandAction 方法中，我只会从那里调用 startApp() 但这不起作用，因为 commandAction 是静态的，而 startApp() 不是。
我已经用尽了所有的可能性，现在我被难住了。任何指导将不胜感激。
在 commandAction 方法内的 CalendarCanvas 页面中，我注释掉了我卡住的地方。我试图让“后退”按钮带我回到应用程序的开头（回到日历）。
import java.io.IOException;
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
/**
* @author addylesson
*/
public class CalendarMidlet extends MIDlet {
private Display mydisplay;
private Command f,e,l;
public CalendarMidlet(){}
public void startApp() {
final Displayable d = new CalendarCanvas(this);
e = new Command("Back", Command.BACK, 0);
f = new Command("Exit", Command.EXIT, 1);
l = new Command("List", Command.SCREEN, 3);
d.addCommand(f);
d.addCommand(e);
d.addCommand(l);
//mList.addCommand(e);
d.setCommandListener(new CommandListener()
{
public void commandAction(Command c, Displayable s)
{
if(c == e)
mydisplay.setCurrent(d);
if(c == l)
//mydisplay.setCurrent(mList);
//else if(c == f)
notifyDestroyed();
}
} );
/*mList.setCommandListener(new CommandListener()
{
public void commandAction(Command c, Displayable s)
{
if(c == e)
mydisplay.setCurrent(d);
else if(c == f)
notifyDestroyed();
}
} );*/
mydisplay = Display.getDisplay(this);
mydisplay.setCurrent(d);
}
public void pauseApp() {
}
public void destroyApp(boolean unconditional) {
}
}
import java.io.IOException;
import java.util.Date;
import javax.microedition.lcdui.*;
import javax.microedition.midlet.MIDlet;
public class CalendarCanvas extends Canvas
{
CalendarWidget calendar = null;
MIDlet midlet = null;
private Alert alert;
private List mList;
private Command f;
private Display mydisplay;
String[] stringElements = { "Celeberity", "Sports", "Zodiac" };
Image[] imageElements = { loadImage("/airplane.png"),
loadImage("/car.png"), loadImage("/hotel.png") };
public CalendarCanvas(final MIDlet m)
{
this.midlet = m;
calendar = new CalendarWidget(new Date());
calendar.headerFont = Font.getFont(Font.FACE_PROPORTIONAL, Font.STYLE_BOLD, Font.SIZE_LARGE);
calendar.weekdayFont = Font.getFont(Font.FACE_PROPORTIONAL, Font.STYLE_BOLD, Font.SIZE_MEDIUM);
calendar.weekdayBgColor = 0xccccff;
calendar.weekdayColor = 0x0000ff;
calendar.headerColor = 0xffffff;
alert = new Alert("Listen", "On this day "
+calendar.getSelectedDate().toString()+ "stuff happened", null, null);
alert.setTimeout(Alert.FOREVER);
mList = new List("Reservation type", List.IMPLICIT,
stringElements, imageElements);
f = new Command("Back", Command.BACK, 0);
mList.addCommand(f);
mList.setCommandListener(new CommandListener()
{
public void commandAction(Command c, Displayable s)
{
if (c == f)
//HOW DO I GET BACK TO THE START OF THE MIDLET??
if (c == List.SELECT_COMMAND) {
int index = mList.getSelectedIndex();
Alert alert2 = new Alert("Your selection",
"You chose " + mList.getString(index) + ".",
null, AlertType.INFO);
mydisplay = Display.getDisplay(midlet);
mydisplay.setCurrent(alert2);
}
}
} );
calendar.initialize();
}
protected void keyPressed(int key)
{
int keyCode = getGameAction(key);
String day = calendar.getSelectedDate().toString();
if(keyCode == FIRE)
{
/*Display.getDisplay(midlet).setCurrent(
new Alert("Selected date",
calendar.getSelectedDate().toString(), null,
AlertType.CONFIRMATION)
);*/
Display.getDisplay(midlet).setCurrent(mList);
}
else
{
calendar.keyPressed(keyCode);
repaint();
}
}
protected void paint(Graphics g)
{
g.setColor(0xffffff);
g.fillRect(0, 0, getWidth(), getHeight());
calendar.paint(g);
}
private Image loadImage(String name)
{
Image image = null;
try {
image = Image.createImage(name);
}
catch (IOException ioe) {
System.out.println(ioe);
}
return image;
}
}
import java.util.Calendar;
import java.util.Date;
import javax.microedition.lcdui.*;
public class CalendarWidget
{
static final String[] MONTH_LABELS = new String[]{
"January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"
};
static final String[] WEEKDAY_LABELS = new String[]{
"M", "T", "W", "T", "F", "S", "S"
};
/* starting week day: 0 for monday, 6 for sunday */
public int startWeekday = 0;
/* elements padding */
public int padding = 2;
/* cells border properties */
public int borderWidth = 4;
public int borderColor = 0x000000;
/* weekday labels properties */
public Font weekdayFont = Font.getDefaultFont();
public int weekdayBgColor = 0x0000ff;
public int weekdayColor = 0xffffff;
/* header (month-year label) properties */
public Font headerFont = Font.getDefaultFont();
public int headerBgColor = 0x0000ff;
public int headerColor = 0xffffff;
/* cells properties */
public Font font = Font.getDefaultFont();
public int foreColor = 0x000000;
public int bgColor = 0x9999ff;
public int selectedBgColor = 0xffff00;
public int selectedForeColor = 0xff0000;
/* internal properties */
int width = 0;
int height = 0;
int headerHeight = 0;
int weekHeight = 0;
int cellWidth = 0;
int cellHeight = 0;
/* internal time properties */
long currentTimestamp = 0;
Calendar calendar = null;
int weeks = 0;
public CalendarWidget(Date date)
{
calendar = Calendar.getInstance();
//we'll see these 2 methods later
setDate(date);
initialize();
}
public Date getSelectedDate()
{
return calendar.getTime();
}
public void setDate(Date d)
{
currentTimestamp = d.getTime();
calendar.setTime(d);
//weeks number can change, depending on week starting day and month total days
this.weeks = (int)Math.ceil(((double)getStartWeekday() + getMonthDays()) / 7);
}
public void setDate(long timestamp)
{
setDate(new Date(timestamp));
}
void initialize()
{
//let's initialize calendar size
this.cellWidth = font.stringWidth("MM") + 3 * padding;
this.cellHeight = font.getHeight() + 15 * padding;
this.headerHeight = headerFont.getHeight() + 2 * padding;
this.weekHeight = weekdayFont.getHeight() + 2 * padding;
this.width = 7 * (cellWidth + borderWidth) + borderWidth;
initHeight();
}
void initHeight()
{
this.height =
headerHeight + weekHeight +
this.weeks * (cellHeight + borderWidth) + borderWidth;
}
int getMonthDays()
{
int month = calendar.get(Calendar.MONTH);
switch(month)
{
case 3:
case 5:
case 8:
case 10:
return 30;
case 1:
return calendar.get(Calendar.YEAR) % 4 == 0 && calendar.get(Calendar.YEAR) % 100 != 0 ? 29 : 28;
default:
return 31;
}
}
int getStartWeekday()
{
//let's create a new calendar with same month and year, but with day 1
Calendar c = Calendar.getInstance();
c.set(Calendar.MONTH, calendar.get(Calendar.MONTH));
c.set(Calendar.YEAR, calendar.get(Calendar.YEAR));
c.set(Calendar.DAY_OF_MONTH, 1);
//we must normalize DAY_OF_WEEK returned value
return (c.get(Calendar.DAY_OF_WEEK) + 5) % 7;
}
public void keyPressed(int key)
{
switch(key)
{
case Canvas.UP:
go(-7);
break;
case Canvas.DOWN:
go(7);
break;
case Canvas.RIGHT:
go(1);
break;
case Canvas.LEFT:
go(-1);
break;
}
}
void go(int delta)
{
int prevMonth = calendar.get(Calendar.MONTH);
setDate(currentTimestamp + 86400000 * delta);
//we have to check if month has changed
//if yes, we have to recalculate month height
//since weeks number could be changed
if(calendar.get(Calendar.MONTH) != prevMonth)
{
initHeight();
}
}
public void paint(Graphics g)
{
//painting background
g.setColor(bgColor);
g.fillRect(0, 0, width, height);
//painting header (month-year label)
g.setFont(headerFont);
g.setColor(headerColor);
g.drawString(MONTH_LABELS[calendar.get(Calendar.MONTH)] + " " + calendar.get(Calendar.YEAR), width / 2, padding, Graphics.TOP | Graphics.HCENTER);
//painting week days labels
g.translate(0, headerHeight);
g.setColor(weekdayBgColor);
g.fillRect(0, 0, width, weekHeight);
g.setColor(weekdayColor);
g.setFont(weekdayFont);
for(int i = 0; i < 7; i++)
{
g.drawString(WEEKDAY_LABELS[(i + startWeekday) % 7],
borderWidth + i * (cellWidth + borderWidth) + cellWidth / 2,
padding,
Graphics.TOP | Graphics.HCENTER
);
}
//painting cells borders
g.translate(0, weekHeight);
g.setColor(borderColor);
for(int i = 0; i <= weeks; i++)
{
g.fillRect(0, i * (cellHeight + borderWidth), width, borderWidth);
}
for(int i = 0; i <= 7; i++)
{
g.fillRect(i * (cellWidth + borderWidth), 0, borderWidth, height - headerHeight - weekHeight);
}
//painting days
int days = getMonthDays();
int dayIndex = (getStartWeekday() - this.startWeekday + 7) % 7;
g.setColor(foreColor);
int currentDay = calendar.get(Calendar.DAY_OF_MONTH);
for(int i = 0; i < days; i++)
{
int weekday = (dayIndex + i) % 7;
int row = (dayIndex + i) / 7;
int x = borderWidth + weekday * (cellWidth + borderWidth) + cellWidth / 2;
int y = borderWidth + row * (cellHeight + borderWidth) + padding;
//if this is the current day, we'll use selected bg and fore colors
if(i + 1 == currentDay)
{
g.setColor(selectedBgColor);
g.fillRect(
borderWidth + weekday * (cellWidth + borderWidth),
borderWidth + row * (cellHeight + borderWidth),
cellWidth, cellHeight);
g.setColor(selectedForeColor);
}
g.drawString("" + (i + 1), x, y, Graphics.TOP | Graphics.HCENTER);
//if this is the current day, we must restore standard fore color
if(i + 1 == currentDay)
{
g.setColor(foreColor);
}
}
//let's traslate back!
g.translate(0, - headerHeight - weekHeight);
}
}