Put FieldManager at center of the screen in a BlackBerry app - blackberry

Question

I know about how to put field on the center of the screen with horizontally and vertically.
However I got success with the field, but I want to set the VerticalFieldManager or HorizontalFieldManage to the center of the screen.
My code is like below, but I am not able to set it at center of the screen.
final Bitmap scale = new Bitmap(Display.getWidth(),Display.getHeight());
_backgroundBitmap.scaleInto(scale, Bitmap.FILTER_LANCZOS);
//==============================
// this manager is used for the static background image
mainManager = new VerticalFieldManager(Manager.USE_ALL_HEIGHT | Manager.USE_ALL_WIDTH | Manager.VERTICAL_SCROLL) {
public void paint(Graphics graphics) {
graphics.clear();
graphics.drawBitmap(0, 0, deviceWidth, deviceHeight,scale, 0, 0);
super.paint(graphics);
}
};
// this manger is used for adding the componentes
subManager = new VerticalFieldManager(Manager.VERTICAL_SCROLL | Manager.VERTICAL_SCROLLBAR) {
/*protected void sublayout(int maxWidth, int maxHeight) {
int displayWidth = deviceWidth;
int displayHeight = deviceHeight;
super.sublayout(displayWidth, displayHeight);
setExtent(displayWidth, displayHeight);
}*/
};
VerticalFieldManager dataManager = new VerticalFieldManager(){};
dataManager.setMargin(20, 20, 20, 20);
//CategoryListLayout
//===============================================================================
//====================================
HorizontalFieldManager categoryLayout = new HorizontalFieldManager(FIELD_VCENTER | USE_ALL_WIDTH | FIELD_HCENTER){
protected void paint(Graphics graphics) {
graphics.setColor(0xFFFFFFFF);
super.paint(graphics);
}
};
LabelField cateName = new LabelField("Category", FIELD_VCENTER){
protected void layout(int width, int height) {
super.layout(width, height);
this.setExtent(150, this.getHeight());
}
};
categoryLayout.setBorder(myBorder);
//choice_country.setMinimalWidth(30);
choice_country.setMargin(10, 10, 10, 10);
categoryLayout.add(cateName);
categoryLayout.add(new BitmapField(Bitmap.getBitmapResource("vertical_line.png"), FIELD_VCENTER));
categoryLayout.add(choice_country);
dataManager.add(categoryLayout);
//===============================================================================
//DistanceListLayout
//===============================================================================
HorizontalFieldManager distanceLayout = new HorizontalFieldManager(FIELD_VCENTER | USE_ALL_WIDTH | FIELD_HCENTER){
protected void paint(Graphics graphics) {
graphics.setColor(0xFFFFFFFF);
super.paint(graphics);
}
};
LabelField distName = new LabelField("Distance", FIELD_VCENTER){
protected void layout(int width, int height) {
super.layout(width, height);
this.setExtent(150, this.getHeight());
}
};
distanceLayout.setBorder(myBorder);
//choice_distance.setMinimalWidth(300);
choice_distance.setMargin(10, 10, 10, 10);
distanceLayout.add(distName);
distanceLayout.add(new BitmapField(Bitmap.getBitmapResource("vertical_line.png"), FIELD_VCENTER));
distanceLayout.add(choice_distance);
dataManager.add(distanceLayout);
//===============================================================================
listNames = new Vector();
listImage = new Vector();
//new GetList().execute(null);
ButtonField b_search = new ButtonField("Search", ButtonField.CONSUME_CLICK | ButtonField.FIELD_HCENTER);
b_search.setMargin(10,10,10,10);
b_search.setChangeListener(new FieldChangeListener() {
public void fieldChanged(Field field, int context) {
if (choice_country.getSelectedIndex() != 0
|| choice_distance.getSelectedIndex() != 0) {
new SubmitSearch().execute(null);
} else {
Dialog.alert("Select atleast One of Two(Category/Distance).");
}
}
});
dataManager.add(b_search);
removeAllScreen();
subManager.add(dataManager);
mainManager.add(subManager);
add(mainManager);
What's wrong in my code?
Update
Here I am using mainManager to display the Background of the app.
subManager is just for container. datamanager is to include mane HorizontalFieldManager.
Now I want is the datamanager is to be display vertically at center of the screen. It not depend on the HorizontalLayout I am going to add in it.

Answer 1

VerticalManager will ignore any vertical modificators like FIELD_VCENTER.
You have to implement your own Manager which will put submanager to center of the screen. Something like this:
protected void sublayout(int maxWidth, int maxHeight) {
submanager.sublayout(displayWidth, displayHeight);
//after sublayout submanager knows his real dimensions
int submanagerWidth = submanager.getWidth();
int submanagerHeight = submanager.getHeight();
int x = (displayWidth - submanagerWidth) >> 1;
int y = (displayHeight - submanagerHeight) >> 1;
setPositionChild(submanager, x, y);
setExtent(displayWidth, displayHeight);
}
In example I assumed that submanager is only one child. But is there are several it's clear how to modify example.
UPDATE
If there are several children (for example 2):
protected void sublayout(int maxWidth, int maxHeight) {
int height = 0;
for (int i = 0; i < 2; i++) {
submanager[i].sublayout(displayWidth, displayHeight);
height += submanager[i].getHeight();
}
int y = (displayHeight - height) >> 1;
if (y < 0)
y = 0;
for (int i = 0; i < 2; i++) {
int submanagerWidth = submanager[i].getWidth();
int submanagerHeight = submanager[i].getHeight();
int x = (displayWidth - submanagerWidth) >> 1;
setPositionChild(submanager[i], x, y);
y += submanagerHeight;
}
setExtent(displayWidth, max(height, submanagerHeight));
}

Answer 2

Why don't you use something like this?
mainManager = new VerticalFieldManager(Manager.USE_ALL_HEIGHT |
Manager.USE_ALL_WIDTH |
Manager.VERTICAL_SCROLL |
DrawStyle.HCENTER /* or DrawStyle.VCENTER */)