deep copy of NSString from an array from a plist

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deep copy of NSString from an array from a plist

(13 posts) (3 voices)

Started 1 year ago by finder39
Latest reply from TBBle

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finder39
Member

ok so i am doing something kind of unique and need a hand.

I have a plist which is set up like this:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>B1</key>
	<array>
		<string>D2</string>
		<string>D3</string>
		<string>D4</string>
	</array>
	<key>D2</key>
	<array>
		<string>F#2</string>
		<string>A2</string>
	</array>
</dict>
</plist>

with many more arrays in it of course. I am trying to grab the string which i do with this function.

-(NSString *) plistReader:(NSString *)previousNote {
	NSDictionary* plist = [ NSDictionary dictionaryWithContentsOfFile:[[NSBundle mainBundle] pathForResource:@"SnowDay" ofType:@"plist"]];//[NSPropertyListSerialization propertyListFromData:plistData mutabilityOption:NSPropertyListImmutable format:&format errorDescription:&error];
	NSArray *possibleNoteList = [plist objectForKey:previousNote];
	int randomNumber = [GeneralHelpers randomNumberBetween:0 andMax:[possibleNoteList count]];
	NSString *newNote = [NSString stringWithFormat:@"%@%@", [possibleNoteList objectAtIndex:randomNumber], @".mp3"];
	lastNotePlayed =  [NSString stringWithFormat:@"%@", [possibleNoteList objectAtIndex:randomNumber]];
	[lastNotePlayed retain];
	return newNote;
}

which works fine and passes the right information back, but because the only way to not have lastNotePlayed (a nsstring that is a variable of the scene) point to a null memory spot is to retain it, it retains the whole nsdictionary which of course causes HORRIBLE leaks.

my question is how can i make a deep copy of the string so that i dont have to worry about the plist and nsdictionary being deallocated

any help would be AMAZING as this is a very key element of my latest project

Posted 1 year ago #

TBBle
Moderator

Retaining lastNotePlayed shouldn't be retaining the dictionary.

Is lastNotePlayed a property or ivar? You're not releasing the old object before you overwrite your reference in the line above the retain.

Posted 1 year ago #
finder39
Member

it is an ivar. should i make it a property?

Posted 1 year ago #

finder39
Member

so after A LOT of playing i got it to work! and with NO LEAKS!!! I will post here what i did to make it work.

in the game scene's header file

NSString *_lastNotePlayed;

and

@property (nonatomic, retain) NSString *lastNotePlayed;

and in the .m is the synthesize of course

@synthesize lastNotePlayed = _lastNotePlayed;

and the function is now this

-(NSString *) plistReader:(NSString *)previousNote {
	NSDictionary* plist = [ NSDictionary dictionaryWithContentsOfFile:[[NSBundle mainBundle] pathForResource:@"SnowDay" ofType:@"plist"]];//[NSPropertyListSerialization propertyListFromData:plistData mutabilityOption:NSPropertyListImmutable format:&format errorDescription:&error];
	NSArray *possibleNoteList = [plist objectForKey:previousNote];
	int randomNumber = [GeneralHelpers randomNumberBetween:0 andMax:[possibleNoteList count]];
	NSString *newNote = [NSString stringWithFormat:@"%@%@", [possibleNoteList objectAtIndex:randomNumber], @".mp3"];
	[self.lastNotePlayed release];
	self.lastNotePlayed =  [[NSString alloc] initWithFormat:@"%@", [possibleNoteList objectAtIndex:randomNumber]];
	return newNote;
}

I hope that this helps people!! :) and thank you TBBle for the idea to use properties!

Posted 1 year ago #

TBBle
Moderator

You mustn't call [self.lastNodePlayed release] to release the old value, as a retain property will do that for you. You're actually double-releasing the old value in this code, and double-retaining the new value. Move the release line to after the alloc and you'll be fine.

And don't forget to set your property to nil in your dealloc. ^_^

By-the-by, if you're not going to use _lastNotePlayed directly, you don't need to define it as an ivar, current iOS/MacOS will create an ivar (named the same as your property) for you.

Also, normally an NSString property should be "copy" not retain, although in this case you know it's not going to be an NSMutableString, so you're OK.

Posted 1 year ago #
finder39
Member

if i dont release i get a memory leak each time i re run the function after the first time. :/

i will delete the ivar and the synthesize and see what happens :)

Posted 1 year ago #
timTheMystic
Member
You could check first to see if it's not null, it'll cover the first case which it should be null initially.
```
if ( _lastNotePlayed != 0 ) {
     [_lastNotePlayed release];
     _lastNotePlayed = 0;
}
```
And you should put something similar in the dealloc as TBBle mentioned as well.
Posted 1 year ago #
finder39
Member

I could do that check it's a good idea

And I will out the stuff in the dealloc function tomorrow. I have an assembler exam at 9:30 am so sleep time now :-)

Posted 1 year ago #

TBBle
Moderator

I didn't say remove the release, I said move it. You're releasing the wrong thing.

@timTheMystic: Cocoa idiom is not to check for nil (not 0, I know they happen to be the same, but... type-safety is as much attitude as syntax. ^_^) but simply send the message. [nil release] is a perfectly valid and sensible thing to do.

Edit: To be clear, this is correct:

-(NSString *) plistReader:(NSString *)previousNote {
	NSDictionary* plist = [ NSDictionary dictionaryWithContentsOfFile:[[NSBundle mainBundle] pathForResource:@"SnowDay" ofType:@"plist"]];//[NSPropertyListSerialization propertyListFromData:plistData mutabilityOption:NSPropertyListImmutable format:&format errorDescription:&error];
	NSArray *possibleNoteList = [plist objectForKey:previousNote];
	int randomNumber = [GeneralHelpers randomNumberBetween:0 andMax:[possibleNoteList count]];
	NSString *newNote = [NSString stringWithFormat:@"%@%@", [possibleNoteList objectAtIndex:randomNumber], @".mp3"];
	// The following line of code releases the old value of self.lastNotePlayed, because it is a "retain" property
	// It also creates an NSString with retain count one, stores it in self.lastNotePlayed, and retains it, because it is a "retain" property
	self.lastNotePlayed =  [[NSString alloc] initWithFormat:@"%@", [possibleNoteList objectAtIndex:randomNumber]];
	// This line balances out the "retain count one" from the above alloc/init.
	[self.lastNotePlayed release];
	// Now self.lastNotePlayed is owned only by the property, which is what you want here.
	// Alternatively, the above two lines of code are equivalent to:
	// self.lastNotePlayed = [NSString stringWithFormat:@"%@", [possibleNoteList objectAtIndex:randomNumber]];
	// Which is the more usual Cocoa idiom.
	return newNote;
}

Posted 1 year ago #

finder39
Member

WOW o.O thank you

I have decided to work with this:

-(NSString *) notePlistReader:(NSString *)previousNote {
	NSDictionary* plist = [ NSDictionary dictionaryWithContentsOfFile:[[NSBundle mainBundle] pathForResource:@"SnowDay" ofType:@"plist"]];
	NSArray *possibleNoteList = [plist objectForKey:previousNote];
	int randomNumber = [GeneralHelpers randomNumberBetween:0 andMax:[possibleNoteList count]];
	NSString *newNote = [NSString stringWithFormat:@"%@%@", [possibleNoteList objectAtIndex:randomNumber], @".mp3"];
	self.lastNotePlayed = [NSString stringWithFormat:@"%@", [possibleNoteList objectAtIndex:randomNumber]];
	return newNote;
}

as i feel that it makes the most sense to me. I was doing that before, but not with it as a retain property so it was getting released to early and causing crashes.

thank you SO MUCH! :) never used properties except in derived classes so never really understood them. I'm starting to slightly understand them more (and read through Ray Wenderlich's blog about it and that helped some). i think im gonna read into them more.

Posted 1 year ago #

timTheMystic
Member
From what I've read, it is usually better to alloc and release when you can, rather than rely on autorelease. Mainly to clear up memory footprints right away, and we all know memory is of great importance when working with these limited devices.

So this may make more sense using a temp. var. Not a big deal though.
```
NSString* lastNotePlayedT =  [[NSString alloc] initWithFormat:@"%@", [possibleNoteList objectAtIndex:randomNumber]];
self.lastNotePlayed = lastNotePlayedT;
[lastNotePlayedT release];
```
I'm from the TMTOWTDI school of thought ... .. .
Posted 1 year ago #
finder39
Member

well I have use instruments and neither way creates a leak, so i am happy.

I am making this for the mac only, not iOS.
also, there is one leak of some NSFile something something, i think its a standard leak for all templates. but its only like 16kb so i'm not to worried. will look into it later if need be

Posted 1 year ago #
TBBle
Moderator

@timeTheMystic: For an object you're putting into a retain property, autorelease is easier to read, and won't make any difference. Autorelease which isn't the last release is cheap. It's the autorelease which then deallocates the object which is expensive and should be avoided on iOS. (There's probably a cache locality advantage to never autoreleasing, I guess. But there's a cache locality advantage for always deallocating with an autorelease in terms of the actual memory management code free-block tracking code)

Posted 1 year ago #

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