Screen layout in blackberry

how screen layout takes place in blackberry? Let’s analyse with a simple experiment.

import net.rim.device.api.ui.Graphics;
import net.rim.device.api.ui.UiApplication;
import net.rim.device.api.ui.component.ButtonField;
import net.rim.device.api.ui.component.Dialog;
import net.rim.device.api.ui.container.MainScreen;

public class Test extends UiApplication {

	Test() {
		System.out.println("app:main constructor");
		TestScreen screen = new TestScreen();
		pushScreen(screen);
	}

	public static void main(String[] arg) {
		System.out.println("app:main");
		Test app = new Test();
		app.enterEventDispatcher();
	}

	// protected boolean acceptsForeground() {
	// System.out.println("app:acceptsForeground");
	// return super.acceptsForeground();
	// }

	public void activate() {
		System.out.println("app:foreground");
		super.activate();
	}

	public void deactivate() {
		System.out.println("app:background");
		super.deactivate();
	}

//	public boolean hasEventThread() {
//		System.out.println("app:has event thread");
//		return super.hasEventThread();
//	}
//
//	public boolean isEventThread() {
//		System.out.println("app:is event thread");
//		return super.isEventThread();
//	}

}

class TestScreen extends MainScreen {

	ButtonField button;

	TestScreen() {
		System.out.println("app:screen constructor");
		button = new ButtonField("click") {
			protected void fieldChangeNotify(int context) {
				Dialog.alert("hi");
				super.fieldChangeNotify(context);
			}

			protected void layout(int width, int height) {
				System.out.println("app:field layout");
				super.layout(width, height);
			}

			protected void paint(Graphics graphics) {
				System.out.println("app:field paint");
				super.paint(graphics);
			}

			protected void drawFocus(Graphics graphics, boolean on) {
				System.out.println("app:field draw focus");
				super.drawFocus(graphics, on);
			}
		};

		add(button);

	}

	protected void sublayout(int width, int height) {
		System.out.println("app:delegate manager sublayout");
		super.sublayout(width, height);
	}

	protected void subpaint(Graphics graphics) {
		button.setLabel("chagne");
		System.out.println("app:delegate manager subpaint");
		super.subpaint(graphics);
	}

	protected void onUiEngineAttached(boolean attached) {
		if (attached) {
			System.out.println("app:onUiEngineAttached");
		} else {
			System.out.println("app:onUiEngine dettached");
		}
		super.onUiEngineAttached(attached);
	}

	protected void onVisibilityChange(boolean visible) {

		if (visible) {
			System.out.println("app:Visibility true");
		} else {
			System.out.println("app:Visibility false");
		}
		super.onVisibilityChange(visible);
	}

	protected void onObscured() {
		System.out.println("app:onObscured");
		super.onObscured();
	}

	protected boolean onSave() {
		System.out.println("app:on save");
		return super.onSave();
	}

	protected void onExposed() {
		System.out.println("app:on exposed");
		super.onExposed();
	}

	protected boolean onSavePrompt() {
		System.out.println("app:on save prompt");
		return super.onSavePrompt();
	}

}

I have commented isEventThread and hasEventThread because
isEventThread called many times and that makes difficult to
analyse output.

1. Just run the application

Starting test
Started test(127)
app:main
Foreground test(127)
app:screen constructor
app:delegate manager sublayout
app:field layout
app:onUiEngineAttached
app:Visibility true
FocusHistory: Focus gained; App Home Screen; Component net.rim.device.apps.internal.ribbon.launcher.RibbonIconField
FocusHistory: Focus lost; App Home Screen; Component net.rim.device.apps.internal.ribbon.launcher.RibbonIconField
FocusHistory: Focus gained; App test; Component TestScreen$1
app:foreground
app:field paint
app:field draw focus
app:field paint

Analysis:
layout called before paint so we can place all calculation of paint to layout method.

2. Now click on the button one dialog will appear.

app:onObscured
FocusHistory: Focus lost; App test; Component TestScreen$1
FocusHistory: Focus gained; App test; Component net.rim.device.api.ui.component.ButtonField

Analysis:
here we can see the difference between visibility and onObscured
3 click ok button.

app:on exposed

4. press on Esc button of blackberry.
app:on save prompt
app:onObscured

5. Click on save button
app:on exposed
app:on save
app:Visibility false
app:onUiEngine detached
Exit test(127)
Foreground net_rim_bb_ribbon_app(70)
FocusHistory: Focus gained; App NoName; Component TestScreen$1
FocusHistory: Focus lost; App NoName; Component TestScreen$1
FocusHistory: Focus gained; App Home Screen; Component net.rim.device.apps.internal.ribbon.launcher.RibbonIconField

6. Click on the End button of blackberry to place this application to background.

Foreground net_rim_bb_ribbon_app(70)
FocusHistory: Focus gained; App Home Screen; Component net.rim.device.apps.internal.ribbon.launcher.RibbonIconField
app:background
FocusHistory: Focus lost; App test; Component TestScreen$1
app:onObscured
app:Visibility false

7. From switch application menu make this application foreground.

switch
Foreground test(129)
app:foreground
FocusHistory: Focus lost; App Home Screen; Component net.rim.device.api.ui.menu.DefaultMenuListField
FocusHistory: Focus gained; App Home Screen; Component net.rim.device.apps.internal.ribbon.launcher.RibbonIconField
FocusHistory: Focus gained; App test; Component TestScreen$1
app:on exposed
FocusHistory: Focus lost; App Home Screen; Component net.rim.device.apps.internal.ribbon.launcher.RibbonIconField
app:Visibility true
app:field paint
app:field draw focus
app:field paint

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