Java me 在LWUIT中，不显示另一窗体的组件

我是使用LWUIT库的J2me开发人员的新手。我正在制作两个表单：一个是

MainMidlet.java

，另一个是

UpgradeApp.java

。问题是，无论组件添加到什么

UpgradeApp.java

上，都不会显示该组件。请帮帮我。
我的代码如下

MainMidlet.java

package com.sun.lwuit.jewelvicinity;
import com.sun.lwuit.Button;
import com.sun.lwuit.Command;
import com.sun.lwuit.Component;
import com.sun.lwuit.Dialog;
import com.sun.lwuit.Display;
import com.sun.lwuit.Form;
import com.sun.lwuit.Image;
import com.sun.lwuit.Label;
import com.sun.lwuit.TextArea;
import com.sun.lwuit.events.ActionEvent;
import com.sun.lwuit.events.ActionListener;
import com.sun.lwuit.layouts.BorderLayout;
import com.sun.lwuit.layouts.FlowLayout;
import com.sun.lwuit.layouts.GridLayout;
import com.sun.lwuit.plaf.UIManager;
import com.sun.lwuit.table.TableLayout.Constraint;
import com.sun.lwuit.util.Resources;
import java.io.IOException;
import javax.microedition.midlet.*;

public class MainMidlet extends MIDlet implements ActionListener
{
    Form frm_Main;
public Button btn_main_Search, btn_main_WishList, btn_main_UpgradeApp, btn_main_Login,                         btn_main_NewUser,btn_main_Help, btn_main_AboutUs, btn_main_ContactUs, btn_main_Feedback, btn_main_Terms,btn_main_Privacy, btn_main_Exit;

public Image img_main_Search, img_main_Wishlist, img_main_UpgradeApp, img_main_Login, img_main_NewUser,img_main_Help, img_main_AboutUs, img_main_ContactUs, img_main_FeedBack, img_main_Terms,img_main_Privacy, img_main_Exit;

public Command cmd_Exit, cmd_Select;

public void startApp()
{
            //--- Use for third soft Button
    //Display.getInstance().setThirdSoftButton(true);
    Display.init(this);

    try
    {
        Resources theme = Resources.open("/LWUITtheme.res");
        UIManager.getInstance().setThemeProps(theme.getTheme(theme.getThemeResourceNames()[0]));
    }
    catch (IOException io)
    {
        io.printStackTrace();
        Dialog.show("Theme Exception", io.getMessage(), "Ok", null);
    }

    frm_Main = new Form("Jewel Vicinity");

    try
    {
        img_main_Search = Image.createImage("/res/btn_main_search.png");
        img_main_Wishlist = Image.createImage("/res/btn_main_wishlist.png");
        img_main_UpgradeApp = Image.createImage("/res/btn_main_upgradeapp.png");
        img_main_Login = Image.createImage("/res/btn_main_login.png");
        img_main_NewUser = Image.createImage("/res/btn_main_newuser.png");
        img_main_Help = Image.createImage("/res/btn_main_help.png");
        img_main_AboutUs = Image.createImage("/res/btn_main_aboutus.png");
        img_main_ContactUs = Image.createImage("/res/btn_main_contactus.png");
        img_main_FeedBack = Image.createImage("/res/btn_main_feedback.png");
        img_main_Terms = Image.createImage("/res/btn_main_terms.png");
        img_main_Privacy = Image.createImage("/res/btn_main_privacy.png");
        img_main_Exit = Image.createImage("/res/btn_main_exit.png");

    }
    catch (IOException io)
    {
        io.printStackTrace();
        Dialog.show("Image not Found!", io.getMessage(), "Ok", null);
    }

    btn_main_Search = new Button("Search", img_main_Search);
    btn_main_WishList = new Button("Wish List", img_main_Wishlist);
    btn_main_UpgradeApp = new Button("Upgrade", img_main_UpgradeApp);
    btn_main_Login = new Button("Login", img_main_Login);
    btn_main_NewUser = new Button("NewUser", img_main_NewUser);
    btn_main_Help = new Button("help", img_main_Help);
    btn_main_AboutUs = new Button("About Us", img_main_AboutUs);
    btn_main_ContactUs = new Button("Contact Us", img_main_ContactUs);
    btn_main_Feedback = new Button("FeedBack", img_main_FeedBack);
    btn_main_Privacy = new Button("Privacy", img_main_Privacy);
    btn_main_Terms = new Button("Terms", img_main_Terms);
    btn_main_Exit = new Button("Exit", img_main_Exit);



    lbl_main_WishList.setTextPosition(Component.BOTTOM);
    lbl_main_WishList.setAlignment(Component.CENTER);
    lbl_main_WishList.getStyle().setMargin(0, 30, 0, 30);

    lbl_main_UpgradeApp = new Label("Upgrade");

    cmd_Exit = new Command("Exit", 1);
    cmd_Select = new Command("Select");


    GridLayout grd_MenuLayout = new GridLayout(4, 3);
    frm_Main.setTitle("Menu");
    frm_Main.setLayout(grd_MenuLayout);
    frm_Main.setScrollableY(true);



        //---- Add Button On Main Form
    frm_Main.addComponent(btn_main_Search);
    frm_Main.addComponent(btn_main_WishList);
    frm_Main.addComponent(btn_main_UpgradeApp);
    frm_Main.addComponent(btn_main_Login);
    frm_Main.addComponent(btn_main_NewUser);
    frm_Main.addComponent(btn_main_Help);
    frm_Main.addComponent(btn_main_AboutUs);
    frm_Main.addComponent(btn_main_ContactUs);
    frm_Main.addComponent(btn_main_Feedback);
    frm_Main.addComponent(btn_main_Terms);
    frm_Main.addComponent(btn_main_Privacy);
    frm_Main.addComponent(btn_main_Exit);

    frm_Main.addCommand(cmd_Select);
    frm_Main.addCommand(cmd_Exit);


    //frm_Main.setCommandListener(this);
    frm_Main.addCommandListener(this);
    frm_Main.show();
}

public void pauseApp() {}

public void destroyApp(boolean unconditional) {}

public void actionPerformed(ActionEvent ae)
{
    Command cmd = ae.getCommand();
    String strcmdName = cmd.getCommandName();
    if(strcmdName.equals("Exit"))
    {
        notifyDestroyed();
    }

    if (strcmdName.equals("Select"))
    {
        if(btn_main_Search.hasFocus())
        {
            //Dialog.show("Search", "Search", "Ok", null);
            Form frm_Search = new Form("Search");
            frm_Search.show();
        }


        if(btn_main_UpgradeApp.hasFocus())
        {

            Form UpgradeApp =  new Form("Upgrade App");
            UpgradeApp.show();
        }
    }
}
}

package com.sun.lwuit.jewelvicinity;


import com.sun.lwuit.Command;
import com.sun.lwuit.Display;
import com.sun.lwuit.Form;
import com.sun.lwuit.Label;
import com.sun.lwuit.events.ActionEvent;
import com.sun.lwuit.events.ActionListener;
import com.sun.lwuit.layouts.FlowLayout;

public class UpgradeApp extends Form implements ActionListener
{
Label lbl_UpgradeApp;
Command cmd_Yes, cmd_No;
Form frm_UpgradeApp;

public UpgradeApp()
{
    Display.init(this);
    frm_UpgradeApp = new Form("Upgrade Application");
    lbl_UpgradeApp = new Label("The New Version of Jewel.");
    cmd_Yes = new Command("Yes", 1);
    cmd_No = new Command("No", 2);

    FlowLayout flw_UpgradeLayout = new FlowLayout(CENTER);
    frm_UpgradeApp.setLayout(flw_UpgradeLayout);
    frm_UpgradeApp.addComponent(lbl_UpgradeApp);
    frm_UpgradeApp.addCommand(cmd_No);
    frm_UpgradeApp.addCommand(cmd_Yes);
    frm_UpgradeApp.addCommandListener(this);
    frm_UpgradeApp.setVisible(true);
    frm_UpgradeApp.show();
}

public void actionPerformed(ActionEvent evt)
{

}
}

UpgradeApp.java

package com.sun.lwuit.jewelvicinity;
import com.sun.lwuit.Button;
import com.sun.lwuit.Command;
import com.sun.lwuit.Component;
import com.sun.lwuit.Dialog;
import com.sun.lwuit.Display;
import com.sun.lwuit.Form;
import com.sun.lwuit.Image;
import com.sun.lwuit.Label;
import com.sun.lwuit.TextArea;
import com.sun.lwuit.events.ActionEvent;
import com.sun.lwuit.events.ActionListener;
import com.sun.lwuit.layouts.BorderLayout;
import com.sun.lwuit.layouts.FlowLayout;
import com.sun.lwuit.layouts.GridLayout;
import com.sun.lwuit.plaf.UIManager;
import com.sun.lwuit.table.TableLayout.Constraint;
import com.sun.lwuit.util.Resources;
import java.io.IOException;
import javax.microedition.midlet.*;

public class MainMidlet extends MIDlet implements ActionListener
{
    Form frm_Main;
public Button btn_main_Search, btn_main_WishList, btn_main_UpgradeApp, btn_main_Login,                         btn_main_NewUser,btn_main_Help, btn_main_AboutUs, btn_main_ContactUs, btn_main_Feedback, btn_main_Terms,btn_main_Privacy, btn_main_Exit;

public Image img_main_Search, img_main_Wishlist, img_main_UpgradeApp, img_main_Login, img_main_NewUser,img_main_Help, img_main_AboutUs, img_main_ContactUs, img_main_FeedBack, img_main_Terms,img_main_Privacy, img_main_Exit;

public Command cmd_Exit, cmd_Select;

public void startApp()
{
            //--- Use for third soft Button
    //Display.getInstance().setThirdSoftButton(true);
    Display.init(this);

    try
    {
        Resources theme = Resources.open("/LWUITtheme.res");
        UIManager.getInstance().setThemeProps(theme.getTheme(theme.getThemeResourceNames()[0]));
    }
    catch (IOException io)
    {
        io.printStackTrace();
        Dialog.show("Theme Exception", io.getMessage(), "Ok", null);
    }

    frm_Main = new Form("Jewel Vicinity");

    try
    {
        img_main_Search = Image.createImage("/res/btn_main_search.png");
        img_main_Wishlist = Image.createImage("/res/btn_main_wishlist.png");
        img_main_UpgradeApp = Image.createImage("/res/btn_main_upgradeapp.png");
        img_main_Login = Image.createImage("/res/btn_main_login.png");
        img_main_NewUser = Image.createImage("/res/btn_main_newuser.png");
        img_main_Help = Image.createImage("/res/btn_main_help.png");
        img_main_AboutUs = Image.createImage("/res/btn_main_aboutus.png");
        img_main_ContactUs = Image.createImage("/res/btn_main_contactus.png");
        img_main_FeedBack = Image.createImage("/res/btn_main_feedback.png");
        img_main_Terms = Image.createImage("/res/btn_main_terms.png");
        img_main_Privacy = Image.createImage("/res/btn_main_privacy.png");
        img_main_Exit = Image.createImage("/res/btn_main_exit.png");

    }
    catch (IOException io)
    {
        io.printStackTrace();
        Dialog.show("Image not Found!", io.getMessage(), "Ok", null);
    }

    btn_main_Search = new Button("Search", img_main_Search);
    btn_main_WishList = new Button("Wish List", img_main_Wishlist);
    btn_main_UpgradeApp = new Button("Upgrade", img_main_UpgradeApp);
    btn_main_Login = new Button("Login", img_main_Login);
    btn_main_NewUser = new Button("NewUser", img_main_NewUser);
    btn_main_Help = new Button("help", img_main_Help);
    btn_main_AboutUs = new Button("About Us", img_main_AboutUs);
    btn_main_ContactUs = new Button("Contact Us", img_main_ContactUs);
    btn_main_Feedback = new Button("FeedBack", img_main_FeedBack);
    btn_main_Privacy = new Button("Privacy", img_main_Privacy);
    btn_main_Terms = new Button("Terms", img_main_Terms);
    btn_main_Exit = new Button("Exit", img_main_Exit);



    lbl_main_WishList.setTextPosition(Component.BOTTOM);
    lbl_main_WishList.setAlignment(Component.CENTER);
    lbl_main_WishList.getStyle().setMargin(0, 30, 0, 30);

    lbl_main_UpgradeApp = new Label("Upgrade");

    cmd_Exit = new Command("Exit", 1);
    cmd_Select = new Command("Select");


    GridLayout grd_MenuLayout = new GridLayout(4, 3);
    frm_Main.setTitle("Menu");
    frm_Main.setLayout(grd_MenuLayout);
    frm_Main.setScrollableY(true);



        //---- Add Button On Main Form
    frm_Main.addComponent(btn_main_Search);
    frm_Main.addComponent(btn_main_WishList);
    frm_Main.addComponent(btn_main_UpgradeApp);
    frm_Main.addComponent(btn_main_Login);
    frm_Main.addComponent(btn_main_NewUser);
    frm_Main.addComponent(btn_main_Help);
    frm_Main.addComponent(btn_main_AboutUs);
    frm_Main.addComponent(btn_main_ContactUs);
    frm_Main.addComponent(btn_main_Feedback);
    frm_Main.addComponent(btn_main_Terms);
    frm_Main.addComponent(btn_main_Privacy);
    frm_Main.addComponent(btn_main_Exit);

    frm_Main.addCommand(cmd_Select);
    frm_Main.addCommand(cmd_Exit);


    //frm_Main.setCommandListener(this);
    frm_Main.addCommandListener(this);
    frm_Main.show();
}

public void pauseApp() {}

public void destroyApp(boolean unconditional) {}

public void actionPerformed(ActionEvent ae)
{
    Command cmd = ae.getCommand();
    String strcmdName = cmd.getCommandName();
    if(strcmdName.equals("Exit"))
    {
        notifyDestroyed();
    }

    if (strcmdName.equals("Select"))
    {
        if(btn_main_Search.hasFocus())
        {
            //Dialog.show("Search", "Search", "Ok", null);
            Form frm_Search = new Form("Search");
            frm_Search.show();
        }


        if(btn_main_UpgradeApp.hasFocus())
        {

            Form UpgradeApp =  new Form("Upgrade App");
            UpgradeApp.show();
        }
    }
}
}

package com.sun.lwuit.jewelvicinity;


import com.sun.lwuit.Command;
import com.sun.lwuit.Display;
import com.sun.lwuit.Form;
import com.sun.lwuit.Label;
import com.sun.lwuit.events.ActionEvent;
import com.sun.lwuit.events.ActionListener;
import com.sun.lwuit.layouts.FlowLayout;

public class UpgradeApp extends Form implements ActionListener
{
Label lbl_UpgradeApp;
Command cmd_Yes, cmd_No;
Form frm_UpgradeApp;

public UpgradeApp()
{
    Display.init(this);
    frm_UpgradeApp = new Form("Upgrade Application");
    lbl_UpgradeApp = new Label("The New Version of Jewel.");
    cmd_Yes = new Command("Yes", 1);
    cmd_No = new Command("No", 2);

    FlowLayout flw_UpgradeLayout = new FlowLayout(CENTER);
    frm_UpgradeApp.setLayout(flw_UpgradeLayout);
    frm_UpgradeApp.addComponent(lbl_UpgradeApp);
    frm_UpgradeApp.addCommand(cmd_No);
    frm_UpgradeApp.addCommand(cmd_Yes);
    frm_UpgradeApp.addCommandListener(this);
    frm_UpgradeApp.setVisible(true);
    frm_UpgradeApp.show();
}

public void actionPerformed(ActionEvent evt)
{

}
}

---

简单回顾一下，您似乎正在调用

Display.init（this）在表单子类中。我建议您使用调试器并遍历代码