java - 如何从Canvas返回MIDlet

我试图弄清楚，在Canvas中的commandAction方法内部时，如何使命令按钮将我带回到MIDlet的开头？ （基本上是重新开始）。

当密钥触发时，我将其带到新的“列表”页面。在该页面上，我有一个后退按钮，理想情况下，我需要将其带回到CalandarMidlet页面。我的逻辑是，在commandAction方法中，我将只从那里调用startApp（），但是由于commandAction是静态的而startApp（）不是，所以这是行不通的。

我已经用尽了所有的可能性，现在我很沮丧。任何指导将不胜感激。

在commandAction方法内部的CalendarCanvas页面中，我注释掉了卡住的位置。我正在尝试使“后退”按钮将我带回到应用程序的开头（返回日历）。

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);
}
}

最佳答案

直接（坦率地说有点愚蠢）的方法是在被卡住的地方调用m.startApp()。 “笨拙”部分是您要调用的并不是完全startApp，而是您正确地说了“带我回到CalendarMidlet页面”。

为了更贴近您的意图，我宁愿选择refactor CalendarMidlet ...

    // ...
    public void startApp() {
        // extract stuff to start over into dedicated method,
        // keep the rest here
        e = new Command("Back", Command.BACK, 0);
        f = new Command("Exit", Command.EXIT, 1);
        l = new Command("List", Command.SCREEN, 3);
        mydisplay = Display.getDisplay(this);
        startOver();
    }

    public void startOver() {
        // encapsulate stuff to start over here
        final Displayable d = new CalendarCanvas(this);

        d.addCommand(f);
        d.addCommand(e);
        d.addCommand(l);
        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();
            }
        } );
        mydisplay.setCurrent(d);
    }
    // ...

...然后稍微调整CalendarCanvas，以使用上方的“更智能”设计...

    // ...
    CalendarMidlet midlet = null; // was declared as MIDlet before

    // ...
    public CalendarCanvas(final CalendarMIDlet m) // parameter was MIDlet
    {

                this.midlet = m;
                // ...
    }

...以便在commandAction中，我可以调用一个满足我需要的方法，而不仅仅是哑巴startApp：

 if (c == f)
     m.startOver(); // take me back to the CalendarMidlet page