Starting one BlackBerry screen from another - multithreading

Question

I've recently run into a snag while putting on the finishing touches for my BlackBerry app. I'm building a login screen which, if the user is successful in logging in, goes to a data loading screen, and then to a home screen. From the home screen, you can use the app. Everything works great but one thing, I can't seamlessly move from the login screen to the loading screen, to the home screen. I can move from the login screen to the loading screen ok, because I'm doing that via a button click which is on the GUI thread, but then I have the login screen at the bottom of the stack and can't get it out using the dismiss method. Once in the loading screen, I can't push the home screen because I'm not doing it via the gui method, though I'm able to update the GUI via the following piece of code:
private void checkData(){
Timer loadingTimer = new Timer();
TimerTask loadingTask = new TimerTask()
{
public void run()
{
// set the progress bar
progressGaugeField.setValue(DataManager.getDataLoaded());
// for repainting the screen
invalidate();
}
};
loadingTimer.scheduleAtFixedRate(loadingTask, 500, 500);
}
Does anyone know how to solve my problem of moving seamlessly from the login screen to the loading screen to the home screen? Note: once I'm at the home screen I'd like to have it be the only screen on the stack.
Thanks!

Answer 1

In this case, you may want to push the home screen of your application first and then push the login screen after it. I am not sure of your situation, but here are the assumptions I am making:
you are storing login information
if login information is not stored, you push the login screen
in a success case, you store login information and proceed to show the home screen
if login fails or is canceled, you don't display the home screen
If these assumptions are reasonably valid, the below code should work nicely for you.
public class YourApp extends UiApplication {
public YourApp() {
final AppHomeScreen screen = new AppHomeScreen();
pushScreen(screen);
if(getLoginInfo() == null) {
final LoginScreen loginScreen = new LoginScreen();
this.invokeLater(new Runnable() {
public void run() {
pushModalScreen(loginScreen);
if(getLoginInfo()==null)
popScreen(screen); //exit the app
}
//perhaps the loading screen populates info in your home screen then pops itself
pushScreen(new LoadingScreen(screen));
}
);
}
}

Answer 2

Have you tried putting the main screen on the stack first (from the Application) and, if no login has been attempted yet, push the login screen? In turn the login screen can push the loading screen. Once loading is completed, pop it out of the stack (from login) and close() login. You will then be back on the main screen with a logged in user.
For the loading to work and track its progress, you can use the following code
LoadingScreen lScreen = new LoadingScreen();
getUiEngine().pushScreen(lScreen);
_invokeIDGame = getApplication().invokeLater(new Runnable() {
public void run() {
// Check to see if the loading is done.
// implement an isLoading function to determine it
if (lScreen.isLoading() == false) {
// Cancel invoking this piece of code again (normally is invoked
// every 500 ms, as specified below)
getApplication().cancelInvokeLater(_invokeIDGame);
// Pop the loading screen off the stack, which returns the user to this screen
getUiEngine().popScreen(lScreen);
// close this screen
close();
}
}
}, 500, true); // rerun this code every 500ms

Answer 3

If you know in code when you need to push the screen, you can use the UiApplication pushScreen function. You start by getting a handle to the current application that has the UI:
UiApplication currentapp = UiApplication.getUiApplication();
You can compare the active screen in order to verify it's your application:
currentapp.getActiveScreen();
Then you can use the UiApplication instance to push your new screen:
currentapp.pushScreen(homeScreen);
I hope that helps :)