Elements disappear after pause and resume - libgdx

Question

Testing my libGDX app in RoboVM, I have encountered a major problem. When I pause my app (by actually going to the Home screen or sending app invites via Facebook) and then return to my app, classes of my games disappear. As if it does not store data properly on the resume() method. First i though it there was a problem of my AssetLoader, but after some debugging I found that the situation is worse. Actual instances of classes and shapes disappear. As if they never existed.
After googling the issue, I found that it might be related to IOSGraphics, but I have not managed to fix the problem.
My IOSLauncher looks something like this, I have erased the Facebook & Google AdMob specific code.
protected IOSApplication createApplication() {
IOSApplicationConfiguration config = new IOSApplicationConfiguration();
config.useAccelerometer = true;
config.useCompass = true;
config.orientationPortrait = true;
config.orientationLandscape = false;
return new IOSApplication(new Game(this), config);
}
#Override
public boolean didFinishLaunching(UIApplication application,
UIApplicationLaunchOptions launchOptions) {
FBSDKApplicationDelegate.getSharedInstance().didFinishLaunching(application, launchOptions);
initialize();
return true;
}
public void initialize() {
//...
}
public static void main(String[] argv) {
NSAutoreleasePool pool = new NSAutoreleasePool();
UIApplication.main(argv, null, IOSLauncher.class);
pool.close();
}
#Override
public void showAds(boolean show) {
//...
}
#Override
public void shareOnFacebook() {
//...
}
#Override
public void inviteFriends() {
//....
}
#Override
public boolean openURL(UIApplication application, NSURL url,
String sourceApplication, NSPropertyList annotation) {
super.openURL(application, url, sourceApplication, annotation);
return FBSDKApplicationDelegate.getSharedInstance().openURL(
application, url, sourceApplication, annotation);
}
#Override
public void didBecomeActive(UIApplication application) {
super.didBecomeActive(application);
FBSDKAppEvents.activateApp();
}
#Override
public void willResignActive(UIApplication application) {
super.willResignActive(application);
}
#Override
public void willTerminate(UIApplication application) {
super.willTerminate(application);
}
}

Answer 1

This sounds similar to a threading bug I once encountered. I fixed it by deferring resize and resume but I'm not sure if it will help in your case. Something like this:
private boolean needResize, needResume;
private void resize (int width, int height){
needResize = true;
}
private void deferredResize ();
if (!needResize) return;
needResize = false;
int width = Gdx.graphics.getWidth();
int height = Gdx.graphics.getHeight();
//move your resize code here
}
private void resume (){
needResume = true;
}
private void deferredResume (){
if (!needResume) return;
needResume = false;
//move your resume code here
}
public void render (){
deferredResize();
deferredResume();
//...
}

Answer 2

I suggest that you start looking for an alternative to RoboVM to avoid more issues in the future, as Robovm was acquired by Microsoft Xamarin (sad but true) and the framework is no longer maintained. License keys (with Libgdx) will continue to work until the 17th of April 2017, there will be no further updates to RoboVM, be it new features or bug fixes.
As far as I know, Libgdx will switch to Multi-OS engine as the default iOS backend for newly created libGDX projects in the next couple of weeks.

Answer 3

After a couple of days filled with headache I found the solution!
LifeCycle methods like pause & resume, hide & show are not always called When they are supposed to be called, therefore data is not stored properly. This issue can completely break your game.
This thing only occurred when testing my game on the iOS platform, mainly when I opened a 3rd party app, Facebook in this case. No such thing found on Android, though.
The only thing I changed on the iOS version was calling the mentioned methods manually to make sure it always pauses and resumes when it has to.