List Class

This class extends the Screen class and implements the interface Choice. This object allows us to create screens with a list of options to select.

The List class has two constructors:

List(String title, int listType)

List(String title, int listType, String[] elements, Image[] images)

The listType defines which type of List we want to create an can be: EXLUSIVE, MULTIPLE and IMPLICIT.

An exclusive List, means that only one option can be selected.

An implicit List, means that the selection of an option triggers an event.

A multiple List, means that many options can be selected at the same time.

Let’s create a MIDlet with an EXCLUSIVE list.

package my.demo;
import javax.microedition.lcdui.Command;
import javax.microedition.lcdui.CommandListener;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Displayable;
import javax.microedition.lcdui.Form;
import javax.microedition.lcdui.List;
import javax.microedition.midlet.MIDlet;
import javax.microedition.midlet.MIDletStateChangeException;
public class HelloWorld extends MIDlet implements CommandListener {
    private Display myDisplay;
    private Form formOptionSelected;
    private Command exitCommand = new Command("Exit", Command.EXIT,1);
    private Command backCommand = new Command("Back", Command.BACK,1);
    private Command selectCommand = new Command("Select", Command.OK,1);
    private String[] options = {"Option A","Option B", "Option C"};
    private List myList;
    public HelloWorld() {
        myDisplay = Display.getDisplay(this);
        myList = new List("Menu", List.EXCLUSIVE, options, null);
        myList.addCommand(exitCommand);
        myList.addCommand(selectCommand);
        myList.setCommandListener(this);
    }
    protected void destroyApp(boolean arg0) throws MIDletStateChangeException {
        notifyDestroyed();
    }
    protected void pauseApp() {
    }
    protected void startApp() throws MIDletStateChangeException {
        myDisplay.setCurrent(myList);
    }
    public void commandAction(Command c, Displayable d) {
        if (c==exitCommand) {
            System.out.println("Exit");
                try {
                    destroyApp(false);
                } catch (MIDletStateChangeException e) {
                    e.printStackTrace();
                }            
        } else if (c==backCommand) {
            myDisplay.setCurrent(myList);
            System.out.println("Back");
        } else if (c==selectCommand) {
            System.out.println("List");
            formOptionSelected = new Form ("Option selected: " + options[myList.getSelectedIndex()]);
            formOptionSelected.addCommand(backCommand);
            formOptionSelected.setCommandListener(this);
            myDisplay.setCurrent(formOptionSelected);
        }
    }
}

When executing this MIDlet, our initial screen will show something like this:

          

When selecting Option A, and pressing the Select event, the following screen is displayed:

          

When selecting Option B, and pressing the Select event, the following screen is displayed:

          

When selecting Option C, and pressing the Select event, the following screen is displayed:

          

Now, let’s create a MIDlet with an IMPLICIT list.

package my.demo;
import javax.microedition.lcdui.Command;
import javax.microedition.lcdui.CommandListener;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Displayable;
import javax.microedition.lcdui.Form;
import javax.microedition.lcdui.List;
import javax.microedition.midlet.MIDlet;
import javax.microedition.midlet.MIDletStateChangeException;
public class HelloWorld extends MIDlet implements CommandListener {
    private Display myDisplay;
    private Form formOption1, formOption2;
    private Command exitCommand = new Command("Exit", Command.EXIT,1);
    private Command backCommand = new Command("Back", Command.BACK,1);
    private List myList;
    public HelloWorld() {
        myDisplay = Display.getDisplay(this);
        myList = new List("Menu", List.IMPLICIT);
        myList.insert(0, "Option2", null);
        myList.insert(0, "Option1", null);
        myList.addCommand(exitCommand);
        formOption1= new Form("Option 1");
        formOption2= new Form("Option 2");
        formOption1.addCommand(backCommand);
        formOption2.addCommand(backCommand);
        myList.setCommandListener(this);
        formOption1.setCommandListener(this);
        formOption2.setCommandListener(this);
    }                                             
    protected void destroyApp(boolean arg0) throws MIDletStateChangeException {
        notifyDestroyed();
    }                                                                                               
    protected void pauseApp() {
    }
    protected void startApp() throws MIDletStateChangeException {
        myDisplay.setCurrent(myList);
    }
    public void commandAction(Command c, Displayable d) {
        if (c==exitCommand) {
            System.out.println("Exit");
                try {
                    destroyApp(false);
                } catch (MIDletStateChangeException e) {
                    e.printStackTrace();
                }            
        } else if (c==backCommand) {
            myDisplay.setCurrent(myList);
            System.out.println("Back");
        } else if (c==myList.SELECT_COMMAND) {
            System.out.println("List");
            switch (myList.getSelectedIndex()) {
            case 0: {
                myDisplay.setCurrent(formOption1);
                break;
                }
            case 1: {
                myDisplay.setCurrent(formOption2);
                break;
            }
            }
        }
    }
}

When executing this MIDlet, our initial screen will show something like this:

          

If you go to Option 1 and select it, the following screen will be displayed:

          

If you select Back, you will be taken to the initial screen.

If you go to Option 2 and select it, the following screen will be displayed:

          

Finally, let’s create a MIDlet with an MULTIPLE list.

package my.demo;
import javax.microedition.lcdui.Command;
import javax.microedition.lcdui.CommandListener;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Displayable;
import javax.microedition.lcdui.Form;
import javax.microedition.lcdui.List;
import javax.microedition.midlet.MIDlet;
import javax.microedition.midlet.MIDletStateChangeException;
public class HelloWorld extends MIDlet implements CommandListener {
    private Display myDisplay;
    private Form formOptionSelected;
    private Command exitCommand = new Command("Exit", Command.EXIT,1);
    private Command backCommand = new Command("Back", Command.BACK,1);
    private Command selectCommand = new Command("Select", Command.OK,1);
    private String[] options = {"Option A","Option B", "Option C"};
    private List myList;
    public HelloWorld() {
        myDisplay = Display.getDisplay(this);
        myList = new List("Menu", List.MULTIPLE, options, null);
        myList.addCommand(exitCommand);
        myList.addCommand(selectCommand);
        myList.setCommandListener(this);
    }
    protected void destroyApp(boolean arg0) throws MIDletStateChangeException {
        notifyDestroyed();
    }
    protected void pauseApp() {
    }
    protected void startApp() throws MIDletStateChangeException {
        myDisplay.setCurrent(myList);
    }
    public void commandAction(Command c, Displayable d) {
        if (c==exitCommand) {
                try {
                    destroyApp(false);
                } catch (MIDletStateChangeException e) {
                    e.printStackTrace();
                }            
        } else if (c==backCommand) {
            myDisplay.setCurrent(myList);
        } else if (c==selectCommand) {
            String selectedOptions = "";
            boolean[] selectedItems = new boolean[myList.size()];
            myList.getSelectedFlags(selectedItems);
            for (int i=0;i<myList.size();i++) {
                if (selectedItems[i]) {
                    selectedOptions = selectedOptions + options[i] + "\n";
                }                             
            }
            formOptionSelected = new Form ("Selected Options:");
            formOptionSelected.append(selectedOptions);
            formOptionSelected.addCommand(backCommand);
            formOptionSelected.setCommandListener(this);
            myDisplay.setCurrent(formOptionSelected);
        }
    }
}

When executing this MIDlet, our initial screen will show something like this:

          

When you select multiple options and hit on the Select command, a new screen will be shown listing all the options selected.