命令在LWUIT中不起作用

我在lwuit中扩展了Form类，并创建了一个具有两个命令Next和Exit的表单类。然后，我创建了一个Midlet来运行，以显示表单。这些命令正在显示，但是单击它们时什么也没有发生。这是我写的代码：

MainForm.java

import com.sun.lwuit.*;
import com.sun.lwuit.events.ActionEvent;
import com.sun.lwuit.events.ActionListener;
import com.sun.lwuit.layouts.GridLayout;

public class MainForm extends Form implements ActionListener{
private Label label;
private RadioButton epl, laliga, seria, uefa, bundesliga;
private Command exit, next;
private String leagueName;
private ButtonGroup bg;
private TestMIDlet midlet;

public MainForm(TestMIDlet midlet){
    this.midlet = midlet;
    setTitle("Main Page");
    GridLayout gl = new GridLayout(6,1);
    setLayout(gl);
    label = new Label("Choose a league to proceed");
    epl = new RadioButton("EPL");
    laliga = new RadioButton("La liga");
    seria = new RadioButton("Seria A");
    bundesliga = new RadioButton("Bundesliga");
    uefa = new RadioButton("UEFA Champions League");
    uefa.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent actionEvent) {
            leagueName = "International Clubs";
        }
    });
    bundesliga.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent actionEvent) {
            leagueName = "Germany";
        }
    });
    seria.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent actionEvent) {
            leagueName = "Italy";
        }
    });
    laliga.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent actionEvent) {
            leagueName = "Spain";
        }
    });
    epl.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent actionEvent) {
            leagueName = "England";
        }
    });
    bg = new ButtonGroup();
    bg.add(epl);
    bg.add(laliga);
    bg.add(seria);
    bg.add(bundesliga);
    bg.add(uefa);
    next = new Command("Next",2);
    exit = new Command("Exit", 2);
    addComponent(label);
    addComponent(epl);
    addComponent(laliga);
    addComponent(seria);
    addComponent(bundesliga);
    addComponent(uefa);
    addCommand(exit);
    addCommand(next);
}

public void actionPerformed(ActionEvent evt) {
    Command c = evt.getCommand();
    if (c == exit){
        midlet.destroyApp(false);
        midlet.notifyDestroyed();
    }
    else if (c == next){
            System.out.println(leagueName);
    }
}

}