Sketches don't want to 'quit' on the phone

Android Processing

ak_eric

Sketches don't want to 'quit' on the phone

in Android Processing • 2 years ago

I've had this problem since I first started putting sketches on my phone (Samsung Captivate, 2.1): Once started, they don't seem to stop. If I either 'present' a sketch to the phone from Processing, or (once it's installed on the phone) I launch it, I can track its status in the Dalvik Debug Monitor. Once started, the processes never seem to turn off. When the sketch is running, if I press the 'back' or 'home' button, I do return back to the phone desktop, but in the DDM, I can still see the process present as running.

The issue is, if I try and launch the app again, it often will misbehave, the most common symptom is having the screen turn black, but the sketch is running (I confirmed this by writing a sketch that had graphics and vibrated... the vibration worked but the graphics didn't). However If I track the "running services" from my phone, the sketch isn't present. So I either have to reboot the phone, or kill the process in the DDM.

Anyone else running into this, and if so, have a solution? It's like the parent Activity doesn't want to quit.

Replies(17)

andres

Re: Sketches don't want to 'quit' on the phone

2 years ago

Additional information about this issue:

1) I installed two Processing sketches on the phone, let's call them A and B.

2) I run A, and then quit using the back button.

3) With a task manager, I can see that A still appears to be running.

4) I run B, quit using the back button.

5) Now the the task manager shows A gone, but B still running.

The phone is a Galaxy S with Android 2.1.

ak_eric

Re: Sketches don't want to 'quit' on the phone

2 years ago

Ok, I think I've tracked this one down.

When I press the "back" button on my phone, the sketch does appear to properly exit. I can relaunch it consistently without issue. However, if I press the home button, this issue is present. Pressing 'home' doesn't seem to kill the sketch.

Since Processing sketches launch from the parent Activity class's onResume() method (uh, right?), and quit from the onPause() method, I simply override onPause() with a call to Activity's finish() method:

void onPause(){
super.onPause();
// kill our sketch, for reals:
super.finish();
}

Calling to finish() moves into the onDestroy() method, exiting the Activity.
http://developer.android.com/reference/android/app/Activity.html#finish()
http://developer.android.com/reference/android/app/Activity.html#ActivityLifecycle
This may have other unforeseen consequences however. For example, if someone calls you in the middle of the sketch I have a feeling it'll just kill the sketch. But maybe that's desirable?

ak_eric

Re: Sketches don't want to 'quit' on the phone

2 years ago

Sigh, never-mind. The above 'fix' doesn't actually fix the 'home button issue'. I can repro with the sketch still staying active. It however does let me restart the app without it misbehaving, which I guess is a slight improvement. I'm not sure why it was working for a while, but has now stopped. I guess I'll just have to remember to use the back button to quit, rather than home :-S

Jesse Sco..

Re: Sketches don't want to 'quit' on the phone

2 years ago

I would guess that this is an OS-specific method to enable multitasking with apps. ??

I am having the same behaviour as you (Nexus One, 2.2), but when I relaunch it after having pressed the home key, the sketch will launch again but not display anything.

If I try to add super.finish() into the void onPause(), the sketch seems to enter and exit several times, but never properly launches...

ak_eric

Re: Sketches don't want to 'quit' on the phone

2 years ago

So weird: When I first added the super.finish(), it seemed to work perfectly. A few hours later it started to display the behavior you describe.

Hack work-around: If you relaunch it, and it has the black screen, quit by pressing the "back" button (not "home"). When you relaunch it again, it should work.

Jesse Sco..

Re: Sketches don't want to 'quit' on the phone

2 years ago

yeah, that's what I did.

ak_eric

Re: Sketches don't want to 'quit' on the phone

2 years ago

So... I think I may have actually found a solution that works ;) Based on a tip from a comment to a post on my blog, 'Lionel' suggested this:

void onResume() {

super.onResume();

redraw();

}

By adding redraw() in the onResume function, it appears that I can now quit (and restart) properly via the back OR home button.

fyi

ckamath

Re: Re: Sketches don't want to 'quit' on the phone

2 years ago

I haven't used DDM but a technique that has worked for me is to define the following:

//Close application when user presses HOME button
public void onUserLeaveHint() { // this only executes when Home is selected.
super.onUserLeaveHint();
onDestroy();
}
public void onDestroy() {
//end game
super.onDestroy(); //call onDestroy on super class
System.exit(0); //shutdown game
}

Does this help?

Jesse Sco..

Re: Sketches don't want to 'quit' on the phone

2 years ago

nice, will test. thanks.

ak_eric

Re: Sketches don't want to 'quit' on the phone

2 years ago

Actually ckamath, it does: I did some testing with the ddms: adding the redraw() call to onResume(), while it does get past the problem I'm having, still leaves the application running in the background when you press the home button. So while you can now close the sketch with either the home or back button and restart it successfully, only the back button actually removes it from memory. I'm sure there is a good reason for this, but I'm not aware of it ;)

After some testing, it looks like it's the System.exit(0) call that is the key. If I add it to onPause()...

void onPause() {

super.onPause();

System.exit(0);

}

...which is called when the sketch exits, the sketch will now physically 'exit' from memory as well when the home button is pressed.

This also means the onResume() \ redraw() calls talked about above are now unneeded: Since the sketch is properly exiting, there is no problem later restarting it. Win.

I also like the info on onUserLeaveHint(), that's good to know too. Thanks!

a__g

Re: Sketches don't want to 'quit' on the phone

2 years ago

You should probably leave it to Android to handle memory... the applications are really only a selection of activities that are loosely coupled together using the Manifest. If you want a specific activity to be removed, ask the system to remove it. Don't force it!

I think a preferred way is calling "finish()" on your activity or using the noHistory attribute.

ak_eric

Re: Sketches don't want to 'quit' on the phone

2 years ago

So much chaos: A day later I try the most recent code I posted above, and the app would load and instantly quit (similar to what was happening to Jesse Scott in his post above). Then re-presenting the sketch to the phone stopped this behavior. So I have no idea what's going on there. But it did prompt more research ;)

Found some interesting things by making a simple sketch that would print when it was in setup(), draw(), and the parent Activity's onPause(), and onResume():

When a sketch is started (for the first time) it goes through these states:

onResume()

setup()

draw()

Now, if you press the back button to exit, the sketch exist immediately, bypassing onPause (& onStop(), & onDestroy()... it just 'exits'). But the sketch physically removes itself from memory that way, which is what I want.

If you press the home button instead to exit, it does exit through onPause(). However, checking DDMS, the sketch is still running in memory. And if you then restart it, you run into the issues mentioned above where the sketch won't display its graphics: It re-enters in onResume(), but setup() and draw() are never called, and my guess is because the sketch is still in memory. This can be solved by embedding redraw() in onResume() which kicks the sketch in-gear, but this doesn't solve the issue of the sketch exiting properly from memory.

The System.exit(0); call in onPause() seemed to work for a while, but I ran into the endless loop of open\quit, so scratch that.

Based on a__g's suggestion I tried embedding finish() in onPause() (which again, is called by pressing the home button): The app still won't exit from memory, but it will restart properly, emulating the effect of embedding redraw(). Interesting. I also tried adding the noHistory attr to the AndroidManifest.xml file for that sketch, but it had no effect.

Sooooo, I finally went back to ckamath's post above using the onUserLeaveHint() & onDestroy() pairing, implementing them exactly has he has done, and everything works great: Pressing the back button exits the sketch & memory immediately (like it always has), and pressing the home button calls to onDestroy() which is overridden with System.exit(0), which then closes the sketch & memory as well. And everything restarts properly as it should (I should have just stuck with that method to begin with ;-) ). The interesting side effect with this technique is that onPause() is never entered, since the back button skips it, and the home button, which used to call to it, is now overridden to call directly to onDestroy(). Nothing wrong with that, but worth noting. The other thing worth noting is that calling System.exit(0) in onDestroy() appears preferable to calling to it in onPause() (due to that open\close loop problem I encountered).

My only fear is that when I try this same code tomorrow, it will behave differently again, which seems to be a theme with this specific troubleshooting process :-)

So hey big Processing brains, maybe just setup the back end to hand this for the user so they never have to? :-)

a__g

Re: Sketches don't want to 'quit' on the phone

2 years ago

The activity is supposed to run in memory until the system deems it unnecessary for whatever reason. This has several reasons which we shouldn't discuss here, you're better of exploring developer.android.com for that

I haven't been able to spot where the PApplet activity fails to update on resume of the PApplet, but you could try the following. See if that works...

void onStop(){
super.onStop();
finish();
}

ak_eric

Re: Sketches don't want to 'quit' on the phone

2 years ago

Unfortunately that has no effect, since the sketch never accesses onStop(): It enters on onResume(), and exits via the home button through onPause(); As a test I put finish() in onPause(), and at that point it did actually go into onStop(). However, it still didn't exit from memory.

a__g

Re: Re: Sketches don't want to 'quit' on the phone

2 years ago

Okay, let me rephrase. You're definately allowed to use System.exit(), but it's probably not desirable because other activities might be existing in your process and if you kill your process, you'll kill all those activities and I assume without giving them a chance at a graceful exit (storing state, saving user data, etc...). Doing this in onPause, of all places, will actually abruptly kill the users application... so if they were to get a phone call whilst playing the final boss in the game you're developing your application process would be killed and all their unsaved data might be lost. So, it's not "illegal" to call System.exit() but it's not the way Google intended.

finish() is actually just a way of calling onDestroy, which kills activities (but doesn't touch the process, which System.exit() does).

First time you launch an activity (if the activity has not previously been started) the activity lifecycle functions will be called in this order.

onCreate()
onStart()
onResume()

If you press the back button you'll call the following functions

onPause()
onStop()
onDestroy()

If you press the home button instead, you'll get the following

onPause()
onStop()

As you can see, what the home button is designed to do is hide your application (or rather activity), but it won't kill it. However, the back button is designed to kill the current activity and move back one step in the activity history. If your application only has one activity that means killing the applikation... but not it's process, cause that's for the system to take care of.

If the activity was destroyed, either by you or the system, the following would be called when starting it again.

onCreate()
onStart()
onResume()

If the activity was not destroyed...

onRestart()
onStart()
onResume()

edit:
onStop is being called, but you probably just can't see it unless you're checking the logs using DDMS. The PDE is probably "unhooked" from the Log after onPause is being called, so you can't actually see any println's inside the PDE from that point onwards. But if you open the log, either in DDMS or through the ADB you'll see the messages.

accessing logs through ADB on linux, mac should be the same, and windows users only need to remove the ./
./adb -d logcat

ak_eric

Re: Sketches don't want to 'quit' on the phone

2 years ago

First off, I appreciate the time you're taking to work through this, I'm definitely learning. Your description of the usage of System.exit(0) makes sense. And you're probably right about the text logging stuff, I'll need to check that later.

So in theory then, the solution is to simply let the sketch sit in memory at all times if the user presses the home button, and just use the redraw() call to kick it back in gear if the user restarts it? I was under the impression that pressing the home button exits the sketch and when you reopen it there is the 'no graphics bug', but based on some more testing it looks like pressing the home button actually just pauses the sketch, and when you relaunch it restarts the previous session?

Slowly... becoming.... more clear..... ;)

a__g

Re: Re: Sketches don't want to 'quit' on the phone

2 years ago

Basically yeah.
My guess is there's something in the way the thread handling done by the sketch pauses or similar when it's gone into "home" view.