Question

I’m an Objective-C newbie and I’m studying iPhone programming.

In my appDelegate, in the -(BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions method, I’ve a class member (@syntethized) called databasePath.

I set its value this way:

databasePath = [self copyDatabaseToDocuments];

I copied the entire copyDatabaseToDocuments method from a wonderful book by Alasdair Allan and made very little changes (the name of the db is the only thing I changed):

-(NSString *)copyDatabaseToDocuments{
    NSFileManager *fileManager = [NSFileManager defaultManager];
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsPath=[paths objectAtIndex:0];
    NSString *filePath = [documentsPath stringByAppendingPathComponent:@"myDb.sqlite"];
    //
    if(![fileManager fileExistsAtPath:filePath]){
        NSString *bundlePath = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"myDb.sqlite"];
        [fileManager copyItemAtPath:bundlePath toPath:filePath error:nil];
    }
    return filePath;
}

I NSLog the databasePath and I regularly get its value (it is a string path and it is not null) after the assignment.

Then, I have a method -(NSMutableArray*)readDatabase:(char*)querySQL I call from a ViewController through a delegate reference.

Anything works fine if -inside this last method- I assign again the value of databasePath.

But, if I don’t assign it again AND I want to use its value (that I suppose it was set in the -(BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions method) the app crashes.

Why?

Answer 1

Make sure that your @property for databasePath looks like this:

@property (nonatomic, retain) NSString *databasePath;

And then set it in this way:

self.databasePath = [self copyDatabaseToDocuments];

It is probably crashing because copyDatabaseToDocuments returns an autoreleased string, and unless you use the self. notation to set databasePath, that autoreleased string can go away at any time.