EXC_BAD_ACCESS when using NSOutlineView

Question

Hi, i'm trying to get a Outline view to display a directory, now I've edited the example from Apple to make it work from any directory I set, except when expanding any node I get "EXEC_BAD_ACCESS" from the NSOutlineView class.

Here is the header file:

#import <Cocoa/Cocoa.h>

@interface SMLDirectoryDataSource : NSObject {
    NSString *rootDirectory;
}

- (int)outlineView:(NSOutlineView *)outlineView numberOfChildrenOfItem:(id)item;
- (BOOL)outlineView:(NSOutlineView *)outlineView isItemExpandable:(id)item;
- (id)outlineView:(NSOutlineView *)outlineView
      child:(int)index
        ofItem:(id)item;
- (id)outlineView:(NSOutlineView *)outlineView objectValueForTableColumn:(NSTableColumn *)tableColumn
        byItem:(id)item;
- (void) setRootDirectory:(NSString *)directory;

@end

@interface SMLDirectoryDataItem : NSObject
{
    NSString *relativePath, *fullPath;
    SMLDirectoryDataItem *parent;
    NSMutableArray *children;
}

//+ (SMLDirectoryDataItem *)rootItem;
- (int)numberOfChildren;// Returns -1 for leaf nodes
- (SMLDirectoryDataItem *)childAtIndex:(int)n;// Invalid to call on leaf nodes
- (NSString *)fullPath;
- (NSString *)relativePath;

@end

And here is the implementation file:

#import "SMLDirectoryDataSource.h"


@implementation SMLDirectoryDataSource
- (id)initWithDirectory:(NSString *)path
{
    rootDirectory = path;
    return self;
}

- (int)outlineView:(NSOutlineView *)outlineView numberOfChildrenOfItem:(id)item
{
    return (item == nil) ? 1 : [item numberOfChildren];
}

- (BOOL)outlineView:(NSOutlineView *)outlineView isItemExpandable:(id)item
{
    return (item == nil) ? NO : ([item numberOfChildren] != -1);
}

- (id)outlineView:(NSOutlineView *)outlineView
      child:(int)index
        ofItem:(id)item
{
    NSLog(@"hi there");
    if(rootDirectory == nil)
      rootDirectory = @"/";
    NSLog(rootDirectory);
    if(item == nil){
     SMLDirectoryDataItem *item = [[SMLDirectoryDataItem alloc] initWithPath:rootDirectory parent:NULL];
     return item;
     [item release];
    }
    else
     return [(SMLDirectoryDataItem *)item childAtIndex:index];
}
/*(
- (id)outlineView:(NSOutlineView *)outlineView
objectValueForTableColumn:(NSTableColumn *)tableColumn
        byItem:(id)item
{
    if(rootDirectory == nil)
     rootDirectory = @"/";
    return rootDirectory;
}
*/
- (void)setRootDirectory:(NSString *)directory
{
    rootDirectory = directory;
}

- (id)outlineView:(NSOutlineView *)outlineView objectValueForTableColumn:(NSTableColumn *)tableColumn byItem:(id)item {
    if(item == nil)
     return rootDirectory;
    else
     return (id)[(SMLDirectoryDataItem *)item relativePath];
}

- (BOOL)outlineView:(NSOutlineView *)outlineView shouldEditTableColumn:(NSTableColumn *)tableColumn item:(id)item {
    return NO;
}

@end

@implementation SMLDirectoryDataItem

//static SMLDirectoryDataItem *rootItem = nil;
#define IsALeafNode ((id)-1)

- (id)initWithPath:(NSString *)path parent:(SMLDirectoryDataItem *)obj
{
    fullPath = [path copy];
    if (self = [super init])
    {
        relativePath = [[path lastPathComponent] copy];
        parent = obj;
    }
    return self;
}


/*+ (SMLDirectoryDataItem *)rootItem
{
    if (rootItem == nil) rootItem = [[SMLDirectoryDataItem alloc] initWithPath:@"/" parent:nil];
    return rootItem;
}*/


// Creates, caches, and returns the array of children
// Loads children incrementally
- (NSArray *)children
{
    if (children == NULL) {
        NSFileManager *fileManager = [NSFileManager defaultManager];
        //NSString *fullPath = [self fullPath];
        BOOL isDir, valid = [fileManager fileExistsAtPath:fullPath isDirectory:&isDir];
        if (valid && isDir) {
      NSArray *array = [fileManager contentsOfDirectoryAtPath:fullPath error:NULL];
      if (!array) {   // This is unexpected
       children = [[NSMutableArray alloc] init];
      } else {
       NSInteger cnt, numChildren = [array count];
       children = [[NSMutableArray alloc] initWithCapacity:numChildren];
       NSString *filename = [[NSString alloc] init];
       for (cnt = 0; cnt < numChildren; cnt++) {
        filename = [fullPath stringByAppendingPathComponent:[array objectAtIndex:cnt]];
        SMLDirectoryDataItem *item = [[SMLDirectoryDataItem alloc] initWithPath:filename parent:self];
        [children addObject:item];
        [item release];
       }
       [filename release];
      }
        } else {
      NSLog(@"is a leaf... strange");
            children = IsALeafNode;
        }
    }
    return children;
}


- (NSString *)relativePath
{
    return relativePath;
}


- (NSString *)fullPath
{
    // If no parent, return our own relative path
    //if (parent == nil) return relativePath;

    // recurse up the hierarchy, prepending each parent’s path
    //return [[parent fullPath] stringByAppendingPathComponent:relativePath];
    return fullPath;
}

- (SMLDirectoryDataItem *)childAtIndex:(int)n
{
    return [[self children] objectAtIndex:n];
}

- (int)numberOfChildren
{
    id tmp = [self children];
    return (tmp == IsALeafNode) ? (0) : [tmp count];
}


- (void)dealloc
{
    if (children != IsALeafNode) [children release];
    [relativePath release];
    [super dealloc];
}

@end

Update: updated the code with the latest version

Answer 1

You aren't managing memory correctly.

(1) This line of code leaks. Autorelease the SMLDirectoryDataItem instance.

    return (item == nil) ? [[SMLDirectoryDataItem alloc] initWithPath:rootDirectory parent:nil] : [item childAtIndex:index];

(2) In your -initWithPath:parent: method, the following line of code does not retain the string. The autorelease pool releases it when drained. This is most likely leading to your crash:

    relativePath = [path lastPathComponent];

Review this:

http://developer.apple.com/mac/library/DOCUMENTATION/Cocoa/Conceptual/MemoryMgmt/MemoryMgmt.html

There are some additional problems in the code (the updated code):

(1) First and foremost, this...

#define IsALeafNode ((id)-1)

.... is completely wrong. You are passing -1 into things that expect objects. Immediate crash if anything retains/autoreleases or otherwise messages that.

(2) Also, you still aren't managing memory correctly. Your -setRootDirectory: method is not retaining the string. I would suggest using an @property and @synthesizing the setter/getter.

(3) Your -children method is leaking strings like a sieve. Specifically, the filename variable's usage is wrong.