java - 在 J2ME 中链接多个页面

Question

我已经学习 J2ME 有几天了。但我有一个大问题；我的移动应用程序大约有 5 个页面:第一个页面扩展了 MIDlet，而其他页面则扩展了表单。加载第一页后，我使用命令切换到其他页面，但是当我到达新页面(扩展形式)时，我附加的所有命令都没有响应。我需要深入了解解决这个问题。我的代码如下；

初始页面；

        /*
     * To change this template, choose Tools | Templates
     * and open the template in the editor.
     */
    package report;

    import javax.microedition.midlet.*;
    import javax.microedition.lcdui.*;
    import org.netbeans.microedition.lcdui.SimpleTableModel;
    import org.netbeans.microedition.lcdui.TableItem;

    /**
     * @author Possicon
     */
    public class Reports extends MIDlet implements CommandListener {

        private boolean midletPaused = false;

        //<editor-fold defaultstate="collapsed" desc=" Generated Fields ">                      
        private Form form;
        private Command SendReport;
        private Command SendPictureReport;
        private Command exitCommand;
        private Command viewReport;
        private Command subscribe;
        private Command spotted;
        private Command sortBy;
        private SimpleTableModel tableModel1;
        //</editor-fold>                    
        /**
         * The Reports constructor.
         */
        public Reports() {
            //startMIDlet();
        }

        //<editor-fold defaultstate="collapsed" desc=" Generated Methods ">                       
        //</editor-fold>                     
        //<editor-fold defaultstate="collapsed" desc=" Generated Method: initialize ">                                           
        /**
         * Initializes the application.
         * It is called only once when the MIDlet is started. The method is called before the <code>startMIDlet</code> method.
         */
        private void initialize() {                                         
            // write pre-initialize user code here

            // write post-initialize user code here
        }                            
        //</editor-fold>                          

        //<editor-fold defaultstate="collapsed" desc=" Generated Method: startMIDlet ">                                        
        /**
         * Performs an action assigned to the Mobile Device - MIDlet Started point.
         */
        public void startMIDlet() {                                      
            // write pre-action user code here

                getDisplay().setCurrent(getForm());


            // write post-action user code here
        }                             
        //</editor-fold>                           

        //<editor-fold defaultstate="collapsed" desc=" Generated Method: resumeMIDlet ">                                         
        /**
         * Performs an action assigned to the Mobile Device - MIDlet Resumed point.
         */
        public void resumeMIDlet() {                                       
            // write pre-action user code here

            // write post-action user code here
        }                              
        //</editor-fold>                            

        //<editor-fold defaultstate="collapsed" desc=" Generated Method: switchDisplayable ">                                              
        /**
         * Switches a current displayable in a display. The <code>display</code> instance is taken from <code>getDisplay</code> method. This method is used by all actions in the design for switching displayable.
         * @param alert the Alert which is temporarily set to the display; if <code>null</code>, then <code>nextDisplayable</code> is set immediately
         * @param nextDisplayable the Displayable to be set
         */
        public void switchDisplayable(Alert alert, Displayable nextDisplayable) {                                            
            // write pre-switch user code here
            Display display = getDisplay();                                               
            if (alert == null) {
                display.setCurrent(nextDisplayable);
            } else {
                display.setCurrent(alert, nextDisplayable);
            }                                             
            // write post-switch user code here
        }                                   
        //</editor-fold>                                 

        //<editor-fold defaultstate="collapsed" desc=" Generated Method: commandAction for Displayables ">                                                 
        /**
         * Called by a system to indicated that a command has been invoked on a particular displayable.
         * @param command the Command that was invoked
         * @param displayable the Displayable where the command was invoked
         */
        public void commandAction(Command command, Displayable displayable) {                                               
            // write pre-action user code here
            if (displayable == form) {                                           
                if (command == SendReport) {                                         
                    // write pre-action user code here
                    getDisplay().setCurrent(new SendReport());

                    // write post-action user code here
                } else if (command == exitCommand) {                                          
                    // write pre-action user code here
                    exitMIDlet();

                    // write post-action user code here
                } else if (command == sortBy) {                                          
                    // write pre-action user code here

                    // write post-action user code here
                } else if (command == spotted) {                                          
                    // write pre-action user code here
                    getDisplay().setCurrent(new Spotted());

                    // write post-action user code here
                } else if (command == subscribe) {                                          
                    // write pre-action user code here
                    //getDisplay().setCurrent(new Subscribe());
                    new Subscribe().getMyDisplay(getDisplay());

                    // write post-action user code here
                }                                                   
            }                                                 
            // write post-action user code here
        }                                             
        //</editor-fold>                                           


        //<editor-fold defaultstate="collapsed" desc=" Generated Getter: form ">                                   
        /**
         * Returns an initiliazed instance of form component.
         * @return the initialized component instance
         */
        public Form getForm() {
            if (form == null) {                                 
                // write pre-init user code here
                form = new Form("Traffic Reports", new Item[] { });                                    
                form.addCommand(getSortBy());
                form.addCommand(getSendReport());
                form.addCommand(getSubscribe());
                form.addCommand(getExitCommand());
                form.addCommand(getSpotted());
                form.setCommandListener(this);                                  
                // write post-init user code here
                loadReports(form);
                //form.append(getTableModel1());
            }                         
            return form;
        }
        //</editor-fold>                       



        //<editor-fold defaultstate="collapsed" desc=" Generated Getter: SendReport ">                                   
        /**
         * Returns an initiliazed instance of SendReport component.
         * @return the initialized component instance
         */
        public Command getSendReport() {
            if (SendReport == null) {                                 
                // write pre-init user code here
                SendReport = new Command("Send Report", Command.SCREEN, 0);                                   
                // write post-init user code here
            }                         
            return SendReport;
        }
        //</editor-fold>                       

        //<editor-fold defaultstate="collapsed" desc=" Generated Getter: SendPictureReport ">                                   
        /**
         * Returns an initiliazed instance of SendPictureReport component.
         * @return the initialized component instance
         */
        public Command getSendPictureReport() {
            if (SendPictureReport == null) {                                 
                // write pre-init user code here
                SendPictureReport = new Command("Send Picture Report", Command.SCREEN, 0);                                   
                // write post-init user code here
            }                         
            return SendPictureReport;
        }
        //</editor-fold>                       

        //<editor-fold defaultstate="collapsed" desc=" Generated Getter: tableModel1 ">                                   
        /**
         * Returns an initiliazed instance of tableModel1 component.
         * @return the initialized component instance
         */
        public SimpleTableModel getTableModel1() {
            if (tableModel1 == null) {                                 
                // write pre-init user code here
                tableModel1 = new SimpleTableModel(new java.lang.String[][] {                                    
                    new java.lang.String[] { "Traffic on Ikorodu road, free" },
                    new java.lang.String[] { "Adeola Odeku is free" },
                    new java.lang.String[] { "Accident on Ahmadu Bellow" }}, null);                                  
                // write post-init user code here
            }                         
            return tableModel1;
        }
        //</editor-fold>                       

        //<editor-fold defaultstate="collapsed" desc=" Generated Getter: exitCommand ">                                   
        /**
         * Returns an initiliazed instance of exitCommand component.
         * @return the initialized component instance
         */
        public Command getExitCommand() {
            if (exitCommand == null) {                                 
                // write pre-init user code here
                exitCommand = new Command("Exit", Command.EXIT, 0);                                   
                // write post-init user code here
            }                         
            return exitCommand;
        }
        //</editor-fold>                       

        //<editor-fold defaultstate="collapsed" desc=" Generated Getter: viewReport ">                                   
        /**
         * Returns an initiliazed instance of viewReport component.
         * @return the initialized component instance
         */
        public Command getViewReport() {
            if (viewReport == null) {                                 
                // write pre-init user code here
                viewReport = new Command("View Reports", Command.SCREEN, 0);                                   
                // write post-init user code here
            }                         
            return viewReport;
        }
        //</editor-fold>                       

        //<editor-fold defaultstate="collapsed" desc=" Generated Getter: subscribe ">                                   
        /**
         * Returns an initiliazed instance of subscribe component.
         * @return the initialized component instance
         */
        public Command getSubscribe() {
            if (subscribe == null) {                                 
                // write pre-init user code here
                subscribe = new Command("Subscribe", Command.SCREEN, 0);                                   
                // write post-init user code here
            }                         
            return subscribe;
        }
        //</editor-fold>                       

        //<editor-fold defaultstate="collapsed" desc=" Generated Getter: spotted ">                                   
        /**
         * Returns an initiliazed instance of spotted component.
         * @return the initialized component instance
         */
        public Command getSpotted() {
            if (spotted == null) {                                 
                // write pre-init user code here
                spotted = new Command("Spotted", Command.SCREEN, 0);                                   
                // write post-init user code here
            }                         
            return spotted;
        }
        //</editor-fold>                       

        //<editor-fold defaultstate="collapsed" desc=" Generated Getter: sortBy ">                                   
        /**
         * Returns an initiliazed instance of sortBy component.
         * @return the initialized component instance
         */
        public Command getSortBy() {
            if (sortBy == null) {                                 
                // write pre-init user code here
                sortBy = new Command("Sort By", Command.SCREEN, 0);                                   
                // write post-init user code here
            }                         
            return sortBy;
        }
        //</editor-fold>                       



        /**
         * Returns a display instance.
         * @return the display instance.
         */
        public Display getDisplay() {
            return Display.getDisplay(this);
        }

        /**
         * Exits MIDlet.
         */
        public void exitMIDlet() {
            switchDisplayable(null, null);
            destroyApp(true);
            notifyDestroyed();
        }

        /**
         * Called when MIDlet is started.
         * Checks whether the MIDlet have been already started and initialize/starts or resumes the MIDlet.
         */
        public void startApp() {
            if (midletPaused) {
                resumeMIDlet();
            } else {
                initialize();
                //Login displayed = Login.displayed(1);
                //getDisplay().setCurrent(new Login());
                startMIDlet();

            }
            midletPaused = false;
        }

        /**
         * Called when MIDlet is paused.
         */
        public void pauseApp() {
            midletPaused = true;
        }

        /**
         * Called to signal the MIDlet to terminate.
         * @param unconditional if true, then the MIDlet has to be unconditionally terminated and all resources has to be released.
         */
        public void destroyApp(boolean unconditional) {
        }

        public void loadReports(Form form){
            String string[] ={"Traffic is here", "Traffic is bad here","Accident Occured here"};
            StringItem st;
            for(int i=0; i<string.length; i++){
                 st = new StringItem("",string[i]);
                 form.append(st);
            }
        }

        /*
        public Array fetchReports(){

        }
         * 
         */

}

第二页；试图调用第一页；

    /*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package report;

import javax.microedition.lcdui.Command;
import javax.microedition.lcdui.CommandListener;
import javax.microedition.lcdui.DateField;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Displayable;
import javax.microedition.lcdui.Form;
import javax.microedition.lcdui.Item;
import javax.microedition.lcdui.ItemStateListener;
import javax.microedition.lcdui.StringItem;
import javax.microedition.lcdui.TextField;

/**
 * @author Possicon
 */
public class Subscribe extends Form implements CommandListener, ItemStateListener {

    private Form form;
    private StringItem label;
    private Display display;
    private Command save;
    private Command subscribe;
    private Command spotted; 
    private Command sendReport ;
    private Command viewReport;
    private Command exit;
    private Command back ;
    private TextField email, phone,route;
    private DateField time , timet;

    /*
    public Subscribe(){
        super("");
    }
     * 
     */

    public  Subscribe() {
        //display = Display.getDisplay(this);
        //display = displ;
        //form = new Form("Traffic Subscription");
        super("Traffic Subscription");
        label = new StringItem("Subscribe to recieve Traffic Alerts: ", "");
        email = new TextField("Email: ", "", 50, TextField.EMAILADDR);
        phone = new TextField("Phone: ", "", 11, TextField.ANY);
        route = new TextField("Road: ", "", 20, TextField.ANY);
        //twitter = new TextField("Twitter: ", "", 20, TextField.);
        time = new DateField("Between: ", DateField.TIME);
        timet = new DateField("To: ", DateField.TIME);
        //DateFielddateField= new DateField(“Date:”, DateField.DATE);
        java.util.Date date = new java.util.Date();
        time.setDate(date);

        append(label);
        append(email);
        append(phone);
        append(route);
        append(time);
        append(timet);

         save = new Command("Save", Command.SCREEN,1);         
         spotted = new Command("Spotted", Command.SCREEN,4);
         sendReport = new Command("Send Report", Command.SCREEN,2);
         viewReport = new Command("Reports", Command.SCREEN,3);
         exit = new Command("Exit", Command.EXIT,0);
         //back = new Command("Back", Command.BACK,0);

        addCommand(exit);
        addCommand(viewReport);
        addCommand(sendReport);               
        addCommand(save);

        addCommand(spotted);

        //return form;
    }


    public void commandAction(Command command, Displayable dsplbl) {

        if (command == sendReport) {
                // write pre-action user code here
               new Reports().switchDisplayable(null,new SendReport());
                //display.setCurrent(new SendReport());

                // write post-action user code here
            } else if (command == exit) {
                // write pre-action user code here
                //exitMIDlet();

                // write post-action user code here
            }  else if (command == spotted) {
                // write pre-action user code here
                display.setCurrent(new Spotted());

                // write post-action user code here
            } 
        }


    public void itemStateChanged(Item item) {

    }

    public void save(){

    }


}

Answer 1

在您的订阅表单中，您没有将 CommandListener 附加到您的订阅表单。因此，在表单上添加命令后，请像 this.setCommandListener(this); 那样附加 CommandListener谢谢