I'm writing a game to help teach my son some phonics: it's my first attempt at programming in Java, although I've previously used other languages. The game has four activities: a splash screen which initializes an array of variables before you dismiss it; another to choose a user; a third to choose which level of the game to play; and a fourth to actually play the game.
My problem was that if you go in and out of the game activity repeatedly, that activity would eventually crash -- logcat showed an OOM error. Watching the heap size as I did this, and looking at a heap dump with MAT, it looked as though I was leaking the whole of the fourth activity -- GC was just not being triggered.
I've tried lots of things to track down and fix the leak -- most of which are, I'm sure improvements (e.g. getting rid of all non-static inner classes from that activity) without fixing the problem. However, I've just tried running the same thing on an emulator (same target and API as my device) and there's no leak -- heap size goes up and down, GC is regularly triggered, it doesn't crash.
So I was going to post the code for the activity on here and ask for help spotting what might be causing the leak, but I'm no longer sure that's the right question. Instead I'm wondering why it works on the emulator, but not the phone... Does anyone have any ideas?
IDE: Android Studio 2.1
Target: Android 6, API 23 (Minimum SDK 8)
Emulator: Android Studio
Device: Sony Xperia Z2 (Now running 6.0.1, but I had the same issue pre recent update, i.e. on API 22)
Code for the activity:
public class GameActivity extends AppCompatActivity implements TextToSpeech.OnInitListener {
//TTS Object
private static TextToSpeech myTTS;
//TTS status check code
private int MY_DATA_CHECK_CODE = 0;
//LevelChooser request code
public static Context gameContext;
private int level;
public static String user;
private Typeface chinacat;
public static Activity gameActivity = null;
private static int[] goldstars = {R.drawable.goldstar1, R.drawable.goldstar2, R.drawable.goldstar3};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_NO_TITLE);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
gameActivity = this;
gameContext = this;
level = getIntent().getIntExtra("level", 1);
user = getIntent().getStringExtra("user");
chinacat = Typeface.createFromAsset(getAssets(), "fonts/chinrg__.ttf");
Intent checkTTSIntent = new Intent();
checkTTSIntent.setAction(TextToSpeech.Engine.ACTION_CHECK_TTS_DATA);
startActivityForResult(checkTTSIntent, MY_DATA_CHECK_CODE);
}
@Override
public void onStop() {
if (myTTS != null) {
myTTS.stop();
}
super.onStop();
}
@Override
public void onDestroy() {
if (myTTS != null) {
myTTS.shutdown();
}
Button ok_button = (Button) findViewById(R.id.button);
ok_button.setOnClickListener(null);
ImageView tickImageView = (ImageView) findViewById(R.id.tickImageView);
tickImageView.setOnClickListener(null);
super.onDestroy();
}
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
if (requestCode == MY_DATA_CHECK_CODE) {
if (resultCode == TextToSpeech.Engine.CHECK_VOICE_DATA_PASS) {
myTTS = new TextToSpeech(this, this);
} else {
Intent installTTSIntent = new Intent();
installTTSIntent.setAction(TextToSpeech.Engine.ACTION_INSTALL_TTS_DATA);
startActivity(installTTSIntent);
}
}
}
public void onInit(int initStatus) {
//if tts initialized, load layout and level and assign listeners for layout elements
if (initStatus == TextToSpeech.SUCCESS) {
myTTS.setLanguage(Locale.ENGLISH);
setContentView(R.layout.activity_main);
ImageView imageView = (ImageView) findViewById(R.id.myImageView);
PhonemeGroup levelGroup = MainActivity.gamelevel[level]; //set possible words
levelGroup.setSubset(); //randomize subset of possible words for actual test
PhonicsWord[] testSet = levelGroup.getSubset(); //fill array of test words
TextView[] targetView = new TextView[3]; //textviews for beginning, middle & end of word
targetView[0] = (TextView) findViewById(R.id.targetWord0);
targetView[1] = (TextView) findViewById(R.id.targetWord1);
targetView[2] = (TextView) findViewById(R.id.targetWord2);
TextView[] answersView = new TextView[3]; //textviews for possible user answer choices
answersView[0] = (TextView) findViewById(R.id.letter0);
answersView[1] = (TextView) findViewById(R.id.letter1);
answersView[2] = (TextView) findViewById(R.id.letter2);
//set first target word, image for word, and possible answers
testSet[0].setWord(levelGroup, targetView, answersView, imageView);
testSet[0].speakWord(myTTS);
//subset index is equal to array index for testSet, but visible to & settable by methods
levelGroup.setSubsetIndex(0);
for(int i=0; i<3; i++) {
answersView[i].setTypeface(chinacat);
}
TextView letter0 = (TextView) findViewById(R.id.letter0);
letter0.setOnClickListener(new LetterOnClickListener(testSet, levelGroup, targetView, answersView, 0) );
TextView letter1 = (TextView) findViewById(R.id.letter1);
letter1.setOnClickListener(new LetterOnClickListener(testSet, levelGroup, targetView, answersView, 1) );
TextView letter2 = (TextView) findViewById(R.id.letter2);
letter2.setOnClickListener(new LetterOnClickListener(testSet, levelGroup, targetView, answersView, 2) );
Button ok_button = (Button) findViewById(R.id.button);
ok_button.setOnClickListener(new OKButtonOnClickListener(testSet, levelGroup, targetView, level) );
ImageView tickImageView = (ImageView) findViewById(R.id.tickImageView);
tickImageView.setOnClickListener(new TickClick(myTTS, testSet, levelGroup, targetView, answersView, imageView) );
imageView.setOnClickListener(new WordImageClick(testSet, levelGroup) );
}
/*else if TODO*/
}
private static class WordImageClick implements View.OnClickListener {
//speaks the test word when the test image is clicked
PhonicsWord[] testSet;
PhonemeGroup levelGroup;
public WordImageClick(PhonicsWord[] testSet, PhonemeGroup levelGroup) {
this.testSet = testSet;
this.levelGroup = levelGroup;
}
@Override
public void onClick(View view) {
testSet[levelGroup.getSubsetIndex()].speakWord(myTTS);
}
}
private static class LetterOnClickListener implements View.OnClickListener {
PhonemeGroup levelGroup;
PhonicsWord currentWord;
PhonicsWord[] testSet;
TextView[] targetView;
TextView[] answersView;
int item;
int phonemeclicked;
public LetterOnClickListener(PhonicsWord[] testSet, PhonemeGroup levelGroup, TextView[] targetView, TextView[] answersView, int phonemeclicked) {
this.testSet = testSet;
this.levelGroup = levelGroup;
this.targetView = targetView;
this.answersView = answersView;
this.phonemeclicked = phonemeclicked;
}
@Override
public void onClick(View view) {
this.item = this.levelGroup.getSubsetIndex();
this.currentWord = this.testSet[item];
int i = currentWord.getOmit_index();
targetView[i].setText(answersView[phonemeclicked].getText());
}
}
private void crossClick(View view) {
view.setVisibility(View.INVISIBLE);
if(view.getTag()==4){
finish();
}
}
The static variable gameActivity is used so that when you've finished a level an external class can call GameActivity.gameActivity.finish() after it's displayed how many stars you've got for the level (it's also used to call GameActivity.gameActivity.findViewById in another external class).
public class ShowStarsWithDelay extends Handler {
public void handleMessage(Message msg) {
ImageView starView = (ImageView) ((LevelEndScreens) msg.obj).starView;
ImageView highscoreView = (ImageView) ((LevelEndScreens) msg.obj).highscoreView;
int num_currentstars = (int) ((LevelEndScreens) msg.obj).num_currentstars;
int num_finalstars = (int) ((LevelEndScreens) msg.obj).num_finalstars;
Boolean highscore = (Boolean) ((LevelEndScreens) msg.obj).highscore;
int[] goldstars = (int[])((LevelEndScreens) msg.obj).goldstars;
if(num_currentstars == num_finalstars) {
if(!highscore) {
starView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
GameActivity.gameActivity.finish();
}
});
}
else {
highscoreView.setImageResource(R.drawable.highscore);
highscoreView.setVisibility(View.VISIBLE);
highscoreView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
GameActivity.gameActivity.finish();
}
});
}
}
else {
starView.setImageResource(goldstars[num_currentstars++]);
Message message = new Message();
LevelEndScreens endScreens = new LevelEndScreens(starView, highscoreView, num_currentstars, num_finalstars, highscore, goldstars);
message.obj = endScreens;
this.sendMessageDelayed(message, 1000);
}
}
}
In general, you want to avoid having any static reference to a Context anywhere in your application (this includes Activity classes, of course). The only reference to a Context which MAY be acceptable is referencing the application context (as there is only one and it is always in memory while your app is alive anyway).
If you need a reference to the calling activity in one of your children, you'll need to pass the context as a parameter, or else use one of the child views methods to retrieve the context (such as getContext() for views and fragments).
More information that should help understand memory leaks and why this is important is here: http://android-developers.blogspot.com/2009/01/avoiding-memory-leaks.html
As an example, in your code for calling finish(), you could safely change it to this:
highscoreView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (v.getContext() instanceof Activity) {
((Activity)v.getContext()).finish();
}
}
});
To sum up, in order to fix your memory leaks, you'll need to remove the static keyword for all of your Context fields.
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