Consider the following method and the caller code block. The method analyses a NSString
and extracts a "http://" string which it passes out by reference as an auto release object.
Without releasing g_scan_result, the program works as expected. But according to non-arc rules, g_scan_result should be released since a retain has been called against it.
My question are :
Why g_scan_result cannot be released ?
Is there anything wrong the way g_scan_result is handled in the posted coding below ?
Is it safe not to release g_scan_result as long as the program runs correctly and the XCode Memory Leak tool does not show leakage ?
Which XCode profile tools should I look into to check and under which subtitle ?
Hope somebody knowledgeable could help.
- (long) analyse_scan_result :(NSString *)scan_result target_url :(NSString **)targ_url {
NSLog (#" RES analyse string : %#", scan_result);
NSRange range = [scan_result rangeOfString:#"http://"
options:NSCaseInsensitiveSearch];
if (range.location == NSNotFound) {
*targ_url = #"";
NSLog(#"fnd string not found");
return 0;
}
NSString *sub_string = [scan_result substringFromIndex : range.location];
range = [sub_string rangeOfString : #" "];
if (range.location != NSNotFound) {
sub_string = [sub_string substringToIndex : range.location];
}
NSLog(#" fnd sub_string = %#", sub_string);
*targ_url = sub_string;
return [*targ_url length];
}
The following is the caller code block, also note that g_scan_result has been declared and initialized (on another source file) as :
NSString *g_scan_result = nil;
Please do send a comment or answer if you have suggestions or find possible errors in code posted here (or above). Xcode memory tools does not seem to show any memory leak. But it may be because I do not know where to look as am new to the memory tools.
{
long url_leng = [self analyse_scan_result:result target_url:&targ_url];
NSLog(#" TAR target_url = %#", targ_url);
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:#"Scanned Result"
message:result
delegate:g_alert_view_delegate
cancelButtonTitle:#"OK"
otherButtonTitles:nil];
if (url_leng) {
// ****** The 3 commented off statements
// ****** cannot be added without causing
// ****** a crash after a few scan result
// ****** cycles.
// ****** NSString *t_url;
if (g_system_status.language_code == 0)
[alert addButtonWithTitle : #"Open"];
else if (g_system_status.language_code == 1)
[alert addButtonWithTitle : #"Abrir"];
else
[alert addButtonWithTitle : #"Open"];
// ****** t_url = g_scan_result;
g_scan_result = [targ_url retain];
// ****** [t_url release];
}
targ_url = nil;
[alert show];
[alert release];
[NSTimer scheduledTimerWithTimeInterval:5.0
target:self
selector:#selector(activate_qr_scanner:)
userInfo:nil
repeats:NO
];
return;
}
I think the mystery has been solved. Thanks for all who are kind enough to have looked into this. The reason is before adding the UIAlertView, coding had been done (on another source file) to assign a raw output string to g_scan_result and display it directly on the current view. So when g_scan_result got released, it is releasing the wrong NSString assigned by some outdated code.
In summary, the wrong NSString got released which is the source of the problem.
The solution is just to remove a single outdated statement. The statement from the old implementation was left there as I thought it wouldn't do any harm (and may even helped to make the variable populated continuously). But it turned out to be a very silly mistake. The only excuse is having very little sleep lately. Being able to find an excuse does serve a purpose. Just hope that it doesn't have to be done very often ...
I am getting a static analysis error in this code which doesn't make any sense to me. The error is:
Reference-counted object is used after it is released
This is glue code to allow for PNG loading in a game originally written in C++.
int pngLoad(const char *filename, pngInfo *info, int format, GLuint *textureName)
{
char fullPath[Engine::Settings::MaxPath];
strcpy(fullPath, filename);
appendAppBundlePath(fullPath);
NSString *path = [NSString stringWithCString:fullPath encoding:NSUTF8StringEncoding];
NSData *data = [[NSData alloc] initWithContentsOfFile:path];
UIImage *image = [[UIImage alloc] initWithData:data];
[data release];
Texture2D *loadedTex = [Texture2D alloc];
// ##### Analyzer claims the object is released here: #####
[loadedTex initWithImage:image format:format];
int didLoad;
// ##### Error is here: #####
if (loadedTex.contentSize.width == 0 || loadedTex.contentSize.height == 0)
{
didLoad = 0;
}
else
{
didLoad = 1;
*textureName = loadedTex.name;
// return texture info
info->ScaleFactor = loadedTex.scaleFactor;
info->Width = (float)image.size.width / (float)info->ScaleFactor;
info->Height = (float)image.size.height / (float)info->ScaleFactor;
info->Alpha = 1;
info->PaddedWidth = loadedTex.pixelsWide;
info->PaddedHeight = loadedTex.pixelsHigh;
}
[loadedTex release];
[image release];
return didLoad;
}
If I use Texture2D *loadedTex = [[Texture2D alloc] retain]; this warning is removed, but then an warning that I've leaked an object comes up, so something is seriously weird here.
initWithImage:format: used to contain a [self release] which shouldn't have been there, which I removed when I found this warning. However, even after a full clean and rebuild, I still get the warning. Am I doing something else wrong? Is something not getting properly cleaned up by the Clean command in Xcode?
The analyzer may be right, at least in a general way.
Texture2D *loadedTex = [Texture2D alloc];
[loadedTex initWithImage:image format:format];
In general, "init" might actually discard the object passed in and return a different one. Whether or not this is the case for "Texture2D" is something I don't know, but if the analyzer is going for the general case then it is right.
You should be able to work around that by using
Texture2D *loadedTex = [Texture2D alloc];
loadedTex=[loadedTex initWithImage:image format:format];
Or by simply combining the two calls, as it is done in most Objective-C examples.
You should always combine the alloc and initXXX call when creating objects, in this case
Texture2D *loadedTex = [[Texture2D alloc] initWithImage:image format:format];
An init method need not return the same object it was called with, it is allowed to return a different object.
In this case your result from loadedTex = [Texture2D alloc] would be released and initWithImage would return a different object (which you discard).
How many custom UIPasteboards can be stored on a single device?I'm curious to know: 1. What the max number of UIPasteboard can be created and what will happen when MAX_NUMBER_OF_PASTEBOARDS is reached and someone tries to add another UIPasteboard to the device.
I conducted a very simple experiment for your question:
NSMutableArray *array = [[NSMutableArray alloc] init];
while (1) {
[array addObject: [UIPasteboard pasteboardWithUniqueName]];
if (array.count%100000==0) {
NSLog(#"%d",array.count);
}
}
Long story short, it's bounded by the amount of available memory on the device. This means you'll get a didReceiveMemoryWarning and eventually, the application allocating the memory for the clipboard will crash.
I got an issue. The scenario is like this: I got an NSOperationQueue that contain various NSOperationQueue that need to waitUntilDone:YES. And I need to update the UI too as the queue or the operation is running. What is the best way to handle this situation?
I have tried performSelectorOnMainThread, but is it necessary to use this method every time I need to update the UI. It is seems not a good solution.
- (void)loadPreviewPageWithMagazineID:(NSString *)magazineID userID:(NSString *)userID {
NSMutableArray *operationArray = [NSMutableArray array];
for (NSInteger i = 1; i <= _numTotalPages; ++i) {
//NSLog(#"currenpage = %d, index = %d",_selectedPage,pageIndex);
NSDictionary *arguments = [NSDictionary dictionaryWithObjectsAndKeys:magazineID,
#"itemID", userID, #"userID", [NSNumber numberWithInt:i],
#"pageNumber", nil];
AFOperation *imageOperation =
[[AFOperation alloc] initWithTarget:self
selector:#selector(savePageToDisk:)
object:arguments];
[imageOperation addObserver:self forKeyPath:#"isFinished" options:0 context:nil];
[imageOperation setUserInfo:arguments];
[operationArray addObject:imageOperation];
[imageOperation release];
}
[_imageQueue addOperations:operationArray waitUntilFinished:YES];
}
- (void)processingMagazine:(NSDictionary *)arguments {
// load pdf document from decrypted data
NSString *userID = [arguments objectForKey:#"userID"];
NSString *magazineID = [arguments objectForKey:#"itemID"];
[self loadPreviewPageWithMagazineID:magazineID userID:userID];
}
So each time to update UI I need to call
[_collectionCoverView performSelectorOnMainThread:#selector(setDownloadProgress:)
withObject:[NSNumber numberWithFloat:progress]
waitUntilDone:YES];
Is there any appropriate way to handle the UI?
I didn understand much from your code. But to accomplish what you want, you can add the UI update code at the end of your AFOperation method. I mean to say, UI will be updated automatically once some processing is done, if you add it in the operation method.
Also generally UI update happens in MainThread. SO there is nothing wrong in calling performSelectorInMainThread.
I am creating a basic guessing game in iOS for my kids, and I think there are some fundamental gaps in my understanding of how I should be creating and releasing objects throughout the lifecycle of the app. I have been reading up on retain and release cycles but I think my issue is more to do with the fundamental architecture of the app and how I may be poorly trying to instantiate and then kill a few key objects of the app.
The problem centers around two specific classes.
I have a game class, which I have designed to hold all the information that the game requires to run. When it is init-ed, it holds all instance variables that point to arrays that hold strings such as the various clues, etc. It's basically a container for all the data that the game requires.
I have a game view controller, that creates and an instance of the game class and queries it so as to present on screen the various elements contained with the game object.
This works perfectly the fine. When the user starts a new game, a new instance of the game class is allocated and init-ed and away they go.
The issue comes in when I come to generate a new game. This happens a number of ways. Either The user finishes the game and starts another one or the user quits the current game and then starts a new one.
In my thinking, I would just release the game object and alloc and init a new one. However, I notice running on the device and looking through the profiler, that the game object isn't released at all.It's still, there and each instantiation of the game creates a new game object with the old one still sitting there with no pointers to it.
Fiddling around with the code, I noticed that I did not implement a dealloc method in the Game class...but when I try to do that, the app crashes, I suspect because I am trying to release a previously released object.
Ideally what I am trying to do is get rid of the old Game object, or replace the old one (overwrite) with a new one each time a new game is started.
However, is this approach wrong? Should I be doing it a completely different way? Such as only ever creating a single instance of the game class and rewriting a method inside that class so as to generate a new set of clues, etc everytime a new game starts and the GameViewController tells it to?
Is there a 'best practice' way to do this?
So you've got an idea of what I am doing, code is below for the GameViewController, where an instance of the Game class is created:
#import "GameViewController.h"
#implementation GameViewController
#synthesize game = _game;
-(void)startNewGameOfLevel:(NSInteger)level
{
if(!_game)
{
Game *g = [[Game alloc]initGamewithLevel:level];
[self setGame:g];
[g release]; g = nil;
}
[self set_currentlevel:[_game _currentLevel]];
// set up popover to show the rounds goal letter
[self setUpPopOver];
}
-(void)quitTheCurrentGameAndStartNewGame
{
[_game release]; _game = nil;
[self clearGamePlayingField];
animationStepIndex = 0;
[self startNewGameOfLevel: _currentlevel];
}
Game class (abridged) with the designated initializer of the Game class:
#import "Game.h"
#implementation Game
#synthesize arrayOfLowerCaseLetters = _arrayOfLowerCaseLetters;
#synthesize arrayOfPhrases= _arrayOfPhrases;
#synthesize goalLetter = _goalLetter;
#synthesize goalPhrase = _goalPhrase;
#synthesize gameLetterPool = _gameLetterPool;
#synthesize _indexForGoalLetter, _numberOfLevelsInGame, _currentLevel, _numberOfWhackHoles, _numberOfLettersInGameLetterPool;
-(id)initGamewithLevel:(NSInteger)level
{
[super init];
//create an array of lower case letters. These will
//contain the full alphabet of all possible letters
NSArray *arrayOfLCLetters = [[NSArray alloc] initWithObjects:#"a", #"b", #"c", #"d",#"e", #"f", #"g", #"h", #"i", #"j", #"k", #"l", #"m", #"n", #"o", #"p", #"qu", #"r", #"s", #"t", #"u", #"v", #"w", #"x",#"y", #"z",#"ch", #"sh", #"th", nil];
[self setArrayOfLowerCaseLetters: arrayOfLCLetters];
[arrayOfLCLetters release];arrayOfLCLetters = nil;
//create an array of phrases.
// These must correspond with each of the letters. e.g. a = apple.
NSArray *phrases= [[NSArray alloc ] initWithObjects:
#"apple",
#"butterfly",
#"cat",
#"dog",
#"egg",
#"frog",
#"ghost",
#"horse",
#"igloo",
#"jam",
#"kite",
#"leaf",
#"moon",
#"nut",
#"orange",
#"pig",
#"queen",
#"rabbit",
#"snake",
#"tree",
#"umbrella",
#"van",
#"water",
#"x-ray",
#"yak",
#"Zebra",
#"chair",
#"shoes",
#"thumb",
nil];
[self setArrayOfPhrases:phrases];
[phrases release]; phrases = nil;
//choose a random number to be the index reference for
// each goal letter and goal phrase.
[self set_indexForGoalLetter:(arc4random()%[_arrayOfLowerCaseLetters count])];
NSLog(#"index for goal letter is:, %i", _indexForGoalLetter);
//set Goal letter and goal phrase
[self setGoalLetter: [_arrayOfLowerCaseLetters objectAtIndex: _indexForGoalLetter]];
[self setGoalPhrase: [_arrayOfPhrases objectAtIndex:_indexForGoalLetter ]];
//set current level
[self set_currentLevel: level];
//[self set_currentLevel: 2];
//set number of whackholes by level
[self set_numberOfWhackHoles: [self numberOfWhackHolesByLevel:_currentLevel]];
//generate size of Letter pool by level
[self set_numberOfLettersInGameLetterPool:[self numberOfLettersInLetterPoolbyLevel:_currentLevel]];
////////////////////////////
/// Game letter pool
///////////////////////////
//set up array ton hold the pool of letters
NSMutableArray *gp = [[NSMutableArray alloc] initWithCapacity:_numberOfLettersInGameLetterPool];
[self setGameLetterPool: gp];
[gp release];gp = nil;
//add the goal letter to this pool
[_gameLetterPool addObject:_goalLetter];
int i = 1;
while (i < _numberOfLettersInGameLetterPool) {
NSString *letter = [_arrayOfLowerCaseLetters objectAtIndex:(arc4random()%[_arrayOfLowerCaseLetters count])];
if ([_gameLetterPool containsObject:letter] == false)
{
[_gameLetterPool addObject:letter];
i++;
}
}
NSLog(#"********** Game created ***************");
NSLog(#"pool of letters is: %#", [_gameLetterPool description]);
NSLog(#"****************************************");
NSLog(#"current goal letter is: %#", _goalLetter);
NSLog(#"****************************************");
NSLog(#"current goal phrase is: %#", _goalPhrase);
NSLog(#"****************************************");
return self;
}
-(void)dealloc
{
[super dealloc];
[_arrayOfLowerCaseLetters release]; _arrayOfLowerCaseLetters = nil;
[_arrayOfPhrases release]; _arrayOfPhrases = nil;
[_goalLetter release];_goalLetter = nil;
[_goalPhrase release]; _goalPhrase = nil;
[_gameLetterPool release];_gameLetterPool = nil;
}
The number one problem is that [super dealloc] must be the absolute last thing you do in -dealloc. This is because it is the dealloc method in NSObject that actually frees the memory, so by the time you get back to it, your instance variable pointers may already be garbage.
Other issues:
In init, do self = [super init]; The super object is allowed to return a different self pointer on init.
startNewGameOfLevel: and quitTheCurrentGameAndStartNewGame should use the property, not the bare instance variable.
-(void)startNewGameOfLevel:(NSInteger)level
{
if(![self game])
{
Game *g = [[Game alloc]initGamewithLevel:level];
[self setGame:g];
[g release]; g = nil;// g = nil, not necessary when it's about to go out of scope
}
[self set_currentlevel:[[self game] _currentLevel]]; // don't use _ to start methods - Apple reserves this convention
// set up popover to show the rounds goal letter
[self setUpPopOver];
}
-(void)quitTheCurrentGameAndStartNewGame
{
[self setGame: nil];
[self clearGamePlayingField];
animationStepIndex = 0;
[self startNewGameOfLevel: _currentlevel];
}
There are probably other issues in the body of your code - make sure you build with static analysis enables - it will catch many of them.