Mysterious extra pixels in ButtonField? - blackberry

Question

I have created a very basic custom layout to set out a menu made up of ButtonFields.
To position them vertically, i split the screen into 6 and then put them at divides 2,3,4 and 5 as is shown in the code.
So for the emulator, the Torch, a Height of 480 would see buttons at 160,240,320 and 400.
However, when I check them, they are all 24 pixels below this, and there seems no obvious reason unless this is just a typical convention I have missed!
package Test;
import net.rim.device.api.system.Display;
import net.rim.device.api.ui.Field;
import net.rim.device.api.ui.container.VerticalFieldManager;
class MenuLayoutManager extends VerticalFieldManager{
public MenuLayoutManager()
{
super();
}
public int getPreferredWidth()
{
int preferredWidth = Display.getWidth();
return preferredWidth;
}
protected void sublayout(int inMaxWidth, int inMaxHeight)
{
int xCentre = Display.getWidth()/2;
int yGap = Display.getHeight() / 6;
int xPos = 0;
int yPos = yGap * 2;
int fieldNo = this.getFieldCount();
for(int index = 0; index<fieldNo; index++)
{
Field aField = this.getField(index);
this.layoutChild(aField, inMaxWidth, inMaxHeight);
xPos = xCentre - (aField.getWidth() / 2);
this.setPositionChild(aField, xPos, yPos);
yPos += yGap;
}
this.setExtent(inMaxWidth, inMaxHeight);
}
}
------Entry point and button creation----
package Test;
import net.rim.device.api.ui.component.ButtonField;
import net.rim.device.api.ui.container.MainScreen;
class MyScreen extends MainScreen
{
public MyScreen(){
super(MainScreen.NO_VERTICAL_SCROLL|MainScreen.NO_VERTICAL_SCROLLBAR);
this.initialize();
}
private void initialize()
{
// Set the displayed title of the screen
this.setTitle(String.valueOf("Ben's Menu"));
MenuLayoutManager mlm = new MenuLayoutManager();
ButtonField Button1 = new ButtonField("New Game");
ButtonField Button2 = new ButtonField("High Scores");
ButtonField Button3 = new ButtonField("Instructions");
ButtonField Button4 = new ButtonField("Exit");
mlm.add(Button1);
mlm.add(Button2);
mlm.add(Button3);
mlm.add(Button4);
this.add(mlm);
}
}

Answer 1

With a MainScreen, you don't get the full display height allocated to the screen contents. (At a minimum, IIRC, there's the title and a separator.) Try using a FullScreen instead and see what happens.