J2ME

ChoiceGroup

ChoiceGroup works very similar to List. However, The ChoiceGroup is indented to place on a form object and the actions can be performed when the its items are selected. The prototype to create a choice group object is:

ChoiceGroup choiceObj=new ChoiceGroup(Title,Type);

The Title argument is used to specify the title of the choice group. The second argument is the type of the choice group. The values of the type can be Choice.EXCLUSIVE, Choice.IMPLICIT, Choice.MULTIPLE, Choice.POPUP, Choice.TEXT_WRAP_DEFAULT, Choice.TEXT_WRAP_OFF, and Choice.TEXT_WRAP_ON.

The element can be added to the choice group by using append method of its object.

choiceObj.append(element,image);

Example:

import javax.microedition.lcdui.*;
import javax.microedition.midlet.*;

public class Cgroup extends MIDlet implements CommandListener, ItemStateListener{
private Display display;
private Form frmchoice;
private Command ba,select;
private ChoiceGroup lst;
private StringItem st;


public Cgroup() {
display = Display.getDisplay(this);

}

public void startApp() {
frmchoice=new Form("Q and A");
ba=new Command("Back",Command.BACK,0);
select=new Command("Select",Command.OK,0);
lst=new ChoiceGroup("Select the correct answer:",Choice.EXCLUSIVE);
st=new StringItem("Q:","How many planets are in the universe?");
frmchoice.append(st);
lst.append("a.5",null);
lst.append("b.9",null);
lst.append("c.10",null);
frmchoice.append(lst);
frmchoice.addCommand(ba);
frmchoice.addCommand(select);
frmchoice.setCommandListener(this);
frmchoice.setItemStateListener(this);

display.setCurrent( frmchoice);
}

public void pauseApp() {}

public void destroyApp(boolean unconditional) {}

public void commandAction(Command c, Displayable s) {
if(c==ba) notifyDestroyed();
else if(c==select) showselecteditem();
}

public void itemStateChanged(Item item) {
if(item==lst) {
System.out.println("You have selected "+lst.getString(lst.getSelectedIndex())+".");
}
}



public void showselecteditem(){
String selectedvalue=lst.getString(lst.getSelectedIndex());
System.out.println("You have selected "+selectedvalue+".");
}

}

ChoiceGroup 

Note: In this example, we provide two ways to perform actions on the  lst choice group. One way is using CommandListerner interface and another is ItemStateListener interface. By using the latter, the actions are performed when the item of the lst choice group is selected. You need to write code for the ItemStateChanged() method to generate the actions.




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