Crash when scrolling in UITableView - object being released unexpectedly - objective-c

Question

**Note: I have updated the code based off of aroth's suggestions - however it is still crashing. The code in the below post is the updated code.
I am trying to create an iPhone app based off of the table-view XCode template (XCode 4). The table view gets populated with the correct data in the proper order - however when I go to scroll through the table the app crashes (sometimes I can scroll through 5 or 10 more cells, sometimes it freezes right away). The table view is being fed from 'Artist' objects within an NSArray which is an IVAR of another 'iPodLibraryParser' object. I believe the problem is that the 'iPodLibraryParser' object is being released prematurely - but I don't understand why.
I have created an iPodLibraryParser object with the following header file:
#import <Foundation/Foundation.h>
#import <MediaPlayer/MediaPlayer.h>
#import <CoreLocation/CoreLocation.h>
#import "ArtistClass.h"
#interface iPodLibraryParser : NSObject {
//Location stuff
CLLocationManager *locationManager;
IBOutlet UITextField *latitudeTextField;
IBOutlet UITextField *longitudeTextField;
IBOutlet UILabel *latitudeLabel;
IBOutlet UILabel *longitudeLabel;
//Music Library Stuff
NSString *currentArtist;
NSString *currentAlbum;
NSMutableArray *artistArray;
NSMutableArray *sortedArtistArray;
}
#property (nonatomic, retain) NSMutableArray *sortedArtistArray;
-(void)parseiPodLibrary;
-(id) initializeiPodLibraryParser;
#end
The relevant code in the .m file of this Class:
#implementation iPodLibraryParser
#synthesize sortedArtistArray;
-(id) initializeiPodLibraryParser{
[super init];
sortedArtistArray = [[NSMutableArray alloc] initWithObjects:nil];
return self;
}
-(void)parseiPodLibrary{
.....
NSArray *sortingArray = [[NSArray alloc] initWithObjects:artistTrackCountSorter,nil];
NSArray *tempSortedArray = [artistArray sortedArrayUsingDescriptors:sortingArray];
[sortedArtistArray removeAllObjects];
[sortedArtistArray addObjectsFromArray:tempSortedArray];
}
Artist object header:
#import <UIKit/UIKit.h>
#import "iPodLibraryParser.h"
#interface ArtistClass : NSObject {
NSString *artistName;
int numberOfTracks;
id artistClassViewController;
}
-(id) initializeArtistObjectWithDocument:(id)myDocument withArtist:(NSString*) artist;
#property (nonatomic, retain) NSString *artistName;
#property (nonatomic, assign) int numberOfTracks;
#end
Table View Controller (called RootViewController from the template being used)
Header:
#import <UIKit/UIKit.h>
#import "iPodLibraryParser.h"
#import "ArtistClass.h"
#interface RootViewController : UITableViewController {
iPodLibraryParser *iPodLibrary;
}
#property (nonatomic, retain) iPodLibraryParser *iPodLibrary;
#end
Relevant code
- (void)viewDidAppear:(BOOL)animated
{
[super viewDidAppear:animated];
NSLog(#"In viewDidAppear");
iPodLibrary = [[iPodLibraryParser alloc] initializeiPodLibraryParser];
[iPodLibrary parseiPodLibrary];
}
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
return 1;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
NSLog(#"there are %i artists in the array", [[iPodLibrary sortedArtistArray] count]);
return [[iPodLibrary sortedArtistArray] count];
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
NSLog(#"in tableView blah");
static NSString *CellIdentifier = #"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];
}
// Configure the cell.
NSLog(#"getting row: %i",indexPath.row);
cell.textLabel.text = [[[iPodLibrary sortedArtistArray] objectAtIndex:indexPath.row] artistName];
return cell;
}
The error is at this line:
cell.textLabel.text = [[[iPodLibrary sortedArtistArray] objectAtIndex:indexPath.row] artistName];
I tried creating an array with Artist objects that I created within the RootViewController - and that works perfectly (can scroll the entire table with no crashes)
Thanks again!
--Edit:
It is interesting to note that I get different errors at different times:
Most of the times it's just EXC_BAD_ACCESS at the line:
cell.textLabel.text = [[[iPodLibrary sortedArtistArray] objectAtIndex:indexPath.row] artistName];
Sometimes it's:
-[UIAutoRotatingWindow isEqualToString:]: unrecognized selector sent to instance 0x1baa80
And another had to do with an unrecognized RGB Selector (very strange).

Answer 1

You problem is when you do this:
sortedArtistArray = [artistArray sortedArrayUsingDescriptors:sortingArray];
The sortedArrayUsingDescriptors method is returning an autoreleased object, so you shouldn't be surprised when it gets released on you without warning.
Moreover, because your init does:
sortedArtistArray = [[NSArray alloc] init];
...and because you don't release it before you assign to it, your code is leaking NSArray instances. I would suggest the following revisions:
Make sortedArtistArray an NSMutableArray*, like:
NSMutableArray* sortedArtistArray;
Don't overwrite the array reference in parseiPodLibrary. Instead just copy the sorted dataset into the mutable array, like:
-(void)parseiPodLibrary{
//.....
NSArray* temp = [artistArray sortedArrayUsingDescriptors:sortingArray];
[sortedArtistArray removeAllObjects];
[sortedArtistArray addObjectsFromArray:temp];
}
Don't call [iPodLibrary retain]; in viewDidAppear. You've already called alloc/init on it, so there is no need to retain it again.
Ensure that you call [iPodLibrary release]; in viewWillDisappear, and [sortedArtistArray release]; in dealloc so that you don't leak memory.

Answer 2

I think it's much more likely that your iPodLibrary variable is over-released than that it's the array. You should troubleshoot by splitting your code into a few lines and seeing where it fails:
NSArray *artistArray = [iPodLibrary sortedArtistArray];
Artist *artist = [artistArray objectAtIndex:indexPath.row];
NSString *name = [artist artistName];
cell.textLabel.text = name;
Is it possible that your implementation of initializeiPodLibraryParser returns an autoreleased object? It shouldn't, as that violates the convention. But it would make sense that that would lead to this problem.
When you call this:
iPodLibrary = [[iPodLibraryParser alloc] initializeiPodLibraryParser];
you're directly assigning the iPodLibrary ivar, so its mutator isn't called and it doesn't matter that the property is marked as retain. If you think it's being implicitly retained, it's likely you're over-releasing it somewhere else. I find you'll understand your own memory management if you use this style to assign properties:
iPodLibraryParser *parser = [[iPodLibraryParser alloc] initializeiPodLibraryParser]; // retain count should be 1 if not autoreleased
[self setIpodLibrary:parser]; // retain count is now 2
[parser release]; // retain count is now 1, will go to zero when you release it in dealloc or viewDidUnload
Finally, I'd move your iPodLibrary initialization from viewDidAppear to viewDidLoad:. That's where you should be initializing your view. And you should be cleaning up anything you initialize there in viewDidUnload, which will be called in a low memory situation.