BlackBerry adding fields to MainScreen through another class - blackberry

Question

I want to make a tab bar that will display at the bottom of a couple of MainScreens, and I thought creating a single class would be the right way to go.
The problem, not surprisingly since I'm new, is that when I try to add a field in my class how does it place it in the MainScreen? Do I have to send some sort of reference to the screen I want to work with?
package mypackage;
import net.rim.device.api.system.Bitmap;
import net.rim.device.api.ui.container.HorizontalFieldManager;
public class CustomTabBar {
private HorizontalFieldManager bar;
public CustomTabBar(){
}
public void buildBar(){
bar = new HorizontalFieldManager();
add(bar); //Where am I adding this?!
Bitmap eventIcon = Bitmap.getBitmapResource("eventsicon.png");
Bitmap eventIcon_hover = Bitmap.getBitmapResource("eventsicon-hover.png");
CustomMenuField eventIconField = new CustomMenuField(eventIcon_hover,eventIcon, "TheatreScreen");
}
}

Answer 1

If you want to add child objects directly to a MainScreen, then yes, you need to pass a reference to the MainScreen around, eg:
public class CustomTabBar {
private HorizontalFieldManager bar;
public void buildBar(MainScreen main) {
bar = new HorizontalFieldManager();
Bitmap eventIcon = Bitmap.getBitmapResource("eventsicon.png");
Bitmap eventIcon_hover = Bitmap.getBitmapResource("eventsicon-hover.png");
CustomMenuField eventIconField = new CustomMenuField(eventIcon_hover,eventIcon, "TheatreScreen");
bar.add(eventIconField);
main.add(bar);
}
}
.
public class MyMainScreen extends MainScreen {
private CustomTabBar tab;
public MyMainScreen() {
...
tab = new CustomTabBar();
tab.buildBar(this);
...
}
}
I think a better solution would be to change your class to extend from HorizontalFieldManager instead of encapsulating it, eg:
public class CustomTabBar extends HorizontalFieldManager {
public CustomTabBar(long style) {
super(style);
Bitmap eventIcon = Bitmap.getBitmapResource("eventsicon.png");
Bitmap eventIcon_hover = Bitmap.getBitmapResource("eventsicon-hover.png");
CustomMenuField eventIconField = new CustomMenuField(eventIcon_hover,eventIcon, "TheatreScreen");
add(eventIconField);
}
}
.
public class MyMainScreen extends MainScreen {
private CustomTabBar tab;
public MyMainScreen() {
...
tab = new CustomTabBar(...);
add(tab);
...
}
}

Answer 2

You need the MainScreen object, and you want to use setStatus(this) to put your tab bar at the bottom of the screen. The status section of the MainScreen stays visible, and is always at the bottom of the screen. The Banner is always at the top, and the Title is just below the banner. Everything else sits in a scrollable area between the title/banner and the status sections of the screen.