center a label horizontally and vertically in blackberry - blackberry

Question

I'm trying to center vertically and horizontally a label in a vertical field manager. I have succeeded to center it horizontally but not vertically. The problem is that none of the style constants I've tried (Field.FIELD_VCENTER, DrawStyle.VCENTER etc.). I get the debugger for BlackBerry JRE 6 and I develop for Bold 9900 device. Can anyone help?
VerticalFieldManager vfm_listeAeroport=new VerticalFieldManager (USE_ALL_WIDTH){
protected void sublayout(int maxWidth, int maxHeight) {
super.sublayout(2*Display.getWidth()/3,70);
setExtent(2*Display.getWidth()/3,70);
}
protected void paint(Graphics g){
super.paint(g);
setBackground(BackgroundFactory.createSolidBackground(0xefc94c));
}
};
String mText = "Liste des Aéroports";
LabelField Label = new LabelField(mText,Field.FIELD_HCENTER) {
public void paint(Graphics graphics){
graphics.setColor(0xffffff);
super.paint(graphics);
}
};
vfm_listeAeroport.add(Label);
add(vfm_listeAeroport);
Thanks!

Answer 1

DrawStyle.VCENTER will center the text within the label, not within it's manager. Eg, the labelfield may have a height of 50px and the manager 100px, DrawStyle will center in the 50px.
I think FIELD_VCENTER is not working because it's within a VerticalFieldManager.
In this case I would just set a margin for the label.
int margin_top = (Display.getHeight() - label.getPreferredHeight()) / 2;
int margin_left = (Display.getWidth() - label.getPreferredWidth()) / 2;
label.setMargin(margin_top,0,0,margin_left);

Answer 2

Just commenting on Kevin's suggested solution that positions the label by using margins and sets the margins based on the Screen height and width.
Kevin is 100% correct. VerticalFieldManager only takes up as much vertical space as is needed, not the whole screen. Use setBackground to set a different background colour to see this in operation.
Kevin's solution makes the size of the contained label bigger, so now the VFM will take up more space.
You do not need to use Kevin's solution to set the left and right Margin - as you have already seen, VFM will centre things horizontally using Field_HCENTER.
The problem with Kevins' solution, and in fact with any solution that attempts to guess how much space is required, is that it will fail when there are other things on the screen, for example a Title area or Banner. The issue is the use of Display.getHeight(), which gets the actual height required, rather than the 'free' space on the screen.
The only time when you know the free space, is when the Field is being laid out. Managers do this in their sublayout() method. So to create a generic 'centring' manager, you need to understand how to create a Manager. You will also need to know a little more about MainScreen and its internal processing. To this end, I recommend the following KB articles from the official BB site:
Custom Manager
Extend Manager
MainScreen explained