A ButtonField to be displayed on all the screens of blackberry - blackberry

Question

I am working on a blackberry app where one of the requirements is that a ButtonField has to be displayed on all the screens of the app? How can this be accomplished, since the ButtonField has to be added after 2-3 controls?
Toolbar
Logo
ButtonField (All the screens should have this button)

Answer 1

There are many, many ways to solve this problem. Without seeing a visual description of all your screens, it's a little difficult to know exactly which one will work best for you. But, here's one option:
Create a base class that extends MainScreen, and have that base class add the ButtonField, and make sure that all other fields are added above the buttonfield. You can do this by adding the button field in a footer, that is then aligned with the screen's bottom edge using MainScreen#setStatus(Field).
public class BaseScreen extends MainScreen {
private ButtonField _bottomButton;
/** Can only be called by screen subclasses */
protected BaseScreen() {
// call BaseScreen(long)
this(MainScreen.VERTICAL_SCROLL | MainScreen.VERTICAL_SCROLLBAR);
}
protected BaseScreen(long style) {
super(style);
_bottomButton = new ButtonField("Press Me!", ButtonField.CONSUME_CLICK | Field.FIELD_HCENTER);
// TODO: customize your button here ...
Manager footer = new HorizontalFieldManager(Field.USE_ALL_WIDTH);
// just use a vertical field manager to center the bottom button horizontally
Manager spacerVfm = new VerticalFieldManager(Field.USE_ALL_WIDTH | Field.FIELD_HCENTER);
spacerVfm.add(_bottomButton);
footer.add(spacerVfm);
setStatus(footer);
}
/** #return the bottom button, if any subclasses need to access it */
protected ButtonField getBottomButton() {
return _bottomButton;
}
}
Here is then an example of how you'll build all your other screens:
public class BaseTestScreen extends BaseScreen implements FieldChangeListener {
public BaseTestScreen() {
super(MainScreen.VERTICAL_SCROLL | MainScreen.VERTICAL_SCROLLBAR);
HorizontalFieldManager toolbar = new HorizontalFieldManager();
toolbar.add(new ButtonField("One", ButtonField.CONSUME_CLICK));
toolbar.add(new ButtonField("Two", ButtonField.CONSUME_CLICK));
toolbar.add(new ButtonField("Three", ButtonField.CONSUME_CLICK));
add(toolbar);
BitmapField logo = new BitmapField(Bitmap.getBitmapResource("icon.png"));
add(logo);
// do this if you want each different screen to be able to handle the
// bottom button click event. not necessary ... you can choose to
// handle the click in the BaseScreen class itself.
getBottomButton().setChangeListener(this);
}
public void fieldChanged(Field field, int context) {
if (field == getBottomButton()) {
Dialog.alert("Button Clicked!");
}
}
}
As you can see, this makes it possible to handle the button click (differently) in each screen class you create. Or, you can choose to handle the clicks in the base class (BaseScreen). You'll have to decide which makes sense for you. If the same action is always taken when clicking the button, and the base screen doesn't need additional information to handle the click, then just handle the click in BaseScreen. If not, handle in the subclasses as I show.
P.S. One disadvantage of this approach is that it forces all your screen classes to extend a common base class (BaseScreen). In some situations, this can be limiting. However, on BlackBerry, it's not uncommon to have all your screens extend MainScreen anyway. That said, such an architectural decision is impossible for me to comment on without understanding more about your app.