Switch from one screen to another on BlackBerry - blackberry

Question

I want to switch from one screen to another - from a category screen to a detail screen - in my BlackBerry app. I don't know how to switch from one screen to another.

Answer 1

If you are in the event thread (the default thread your program runs on if it's a UI application and you haven't started any other threads), then opening up another screen can be done by calling the pushScreen() method of the UiApplication class.
Since, in a typical case, your application derives from UiApplication, you would take a reference to your application object and call pushScreen() on it with the parameter of your new screen:
myApp.pushScreen(new MyNewScreen());
If you're running in a worker thread, or in any context where you either don't have access to a UiApplication or pushing a screen would not be allowed (you're only allowed to work with UI components on the original UI thread), then pushing a screen onto the screen stack is a bit different -- you need to switch to the UI thread, and then push the new screen onto the screen stack:
Application.getApplication().invokeLater(
new Runnable() {
public void run() {
Ui.getUiEngine().pushScreen(new MyNewScreen());
}
}
);
At Antair, we have a simple ScreenChanger class that’s part of a larger internal library that we use for all of our projects. Here’s a stripped-down version of the ScreenChanger class for you to use.
// -----------------------------------------------------------------------------
//
// Antair Library for BlackBerry Devices
// ScreenChanger.java
//
// -----------------------------------------------------------------------------
package com.antair.blackberrylib.ui;
import net.rim.device.api.system.Application;
import net.rim.device.api.ui.Screen;
import net.rim.device.api.ui.Ui;
interface ScreenChangerListener
{
void onScreenChangeComplete(Screen openedScreen, Screen closedScreen);
}
final class ScreenChanger
{
static void change ( Screen screenToOpen, ScreenChangerListener listener )
{
ScreenChanger.change(screenToOpen, null, listener);
}
static void change ( Screen screenToOpen, Screen screenToClose,
ScreenChangerListener listener )
{
Application.getApplication().invokeLater(
new EventThreadScreenChanger(screenToOpen, screenToClose, listener));
}
static void close ( Screen screenToClose, ScreenChangerListener listener )
{
Application.getApplication().invokeLater(
new EventThreadScreenChanger(null, screenToClose, listener));
}
}
final class EventThreadScreenChanger extends Thread
{
Screen _screenToOpen;
Screen _screenToClose;
ScreenChangerListener _listener;
EventThreadScreenChanger ( Screen screenToOpen, Screen screenToClose,
ScreenChangerListener listener )
{
_screenToOpen = screenToOpen;
_screenToClose = screenToClose;
_listener = listener;
}
public void run()
{
if ( _screenToOpen != null )
{
try
{
Ui.getUiEngine().pushScreen(_screenToOpen);
}
catch ( Exception e )
{
// Your error handler
}
}
if ( _screenToClose != null )
{
try
{
Ui.getUiEngine().popScreen(_screenToClose);
}
catch ( Exception e )
{
// Your error handler
}
}
if ( _listener != null )
{
_listener.onScreenChangeComplete(_screenToOpen, _screenToClose);
}
}
}