Question

If I release my first array after I copied it to the second array my app crashes. If I autorelease the first array everything works fine. Why? Is there a better way to copy the first array to the second array?

If I call this method I get a ECX_BAD_ACCESS, I am passing an empty array

-(NSArray *)loadSystemDetails
{
    AssortedCodeSnippets *acs = [[AssortedCodeSnippets alloc] init];
    NSArray *details;
    NSString *fp = [self tempPathAndFileName:[self systemDetailsFileName]];
    if ([acs fileExistsAtPath:fp]) {
        NSArray *array = [[NSArray alloc] initWithContentsOfFile:fp];
        details = array;
        [array release];
    } else {
        NSLog(@"No File to Load");
        CreateSystem *cls = [[CreateSystem alloc] init];
        details = [cls loadData];
        [cls release];
        [self saveDataFile:details toPath:fp];
    }
    NSLog(@"details: %@",details);
    [acs release];
    return details;
}

If I autorelease array it work fine.

-(NSArray *)loadSystemDetails
{
    AssortedCodeSnippets *acs = [[AssortedCodeSnippets alloc] init];
    NSArray *details;
    NSString *fp = [self tempPathAndFileName:[self systemDetailsFileName]];
    if ([acs fileExistsAtPath:fp]) {
        NSArray *array = [[[NSArray alloc] initWithContentsOfFile:fp]autorelease];
        details = array;
    } else {
        NSLog(@"No File to Load");
        CreateSystem *cls = [[CreateSystem alloc] init];
        details = [cls loadData];
        [cls release];
        [self saveDataFile:details toPath:fp];
    }

Answer 1

Let’s step through this

Key: M = release/retain message, C = sum of the release/retain messages

                                                              // +----+---+
                                                              // | M  | C |
                                                              // +----+---+
NSArray *array = [[NSArray alloc] initWithContentsOfFile:fp]; // | +1 | 1 |
details = array;                                              // |  0 | 1 |
[array release];                                              // | -1 | 0 |
                                                              // +----+---+

At this point you can see that you are going to be returning details which has a count of 0 therefore will have been deallocated already = crash.

Copy is the wrong term as you do not actually need a copy as such you just want your pointer details to point to a valid object therefore the following would be more correct

- (NSArray *)systemDetails
{
    NSString *filePath = [self tempPathAndFileName:[self systemDetailsFileName]];

    NSArray *details = [[[NSArray alloc] initWithContentsOfFile:filePath] autorelease];

    if (!details) {

        NSLog(@"No File to Load");
        CreateSystem *cls = [[CreateSystem alloc] init];
        details = [cls loadData];
        [cls release]; cls = nil;
        [self saveDataFile:details toPath:filePath];

    }

    NSLog(@"details: %@",details);

    return details;
}

Here I am taking advantage of NSArray‘s method

initWithContentsOfFile:

…[returns] nil if the file can’t be opened or the contents of the file can’t be parsed into an array

This cuts down some of the cruft and makes the method a bit easier to read. I also expanded the variable names to meaningful names (personal preference).

I have also renamed the method as the load art is superflous as essentially you are returning the system details the fact that they are being loaded is not not really a concern to the caller of the method.

It’s also important to note that the other answers suggest that you take an additional retain/copy and then remember to release the returned result later on. This goes against cocoa convention as the method name does not contain new/init/copy therefore the callers f the method should not end up owning the result.