iPhone (iOS): copying files from main bundle to documents folder causes crash

Question

I am trying to set up my application so that on first launch, a series of files located in the "Populator" folder in the main bundle are copied into the documents directory.

My current implementation is as follows:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {

  NSString *documentsDirectory = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
  NSString *sourcePath = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"Populator"];
  NSString *folderPath = [documentsDirectory stringByAppendingPathComponent:@"Files"];
  NSLog(@"Source Path: %@\n Documents Path: %@ \n Folder Path: %@", sourcePath, documentsDirectory, folderPath);

  NSError *error;

  [[NSFileManager defaultManager] copyItemAtPath:sourcePath 
                                        toPath:folderPath
                                         error:&error];

  NSLog(@"Error description-%@ \n", [error localizedDescription]);
  NSLog(@"Error reason-%@", [error localizedFailureReason]);
  ....
  return YES;
}

However this crashes the first time it is run with the following console messages (but the files are copied over). The next time the app is opened, it does not crash.

    2010-07-13 15:14:26.418 AppName[5201:207] Source Path: /Users/jack/Library/Application Support/iPhone Simulator/3.2/Applications/1076C1FA-60B0-4AC7-8CD4-74F81472DAE6/AppName.app/Populator
 Documents Path: /Users/jack/Library/Application Support/iPhone Simulator/3.2/Applications/1076C1FA-60B0-4AC7-8CD4-74F81472DAE6/Documents 
 Folder Path: /Users/jack/Library/Application Support/iPhone Simulator/3.2/Applications/1076C1FA-60B0-4AC7-8CD4-74F81472DAE6/Documents/Files
2010-07-13 15:14:26.466 AppName[5201:207] *** +[AppNameAppDelegate localizedDescription]: unrecognized selector sent to class 0xa79c
2010-07-13 15:14:26.475 AppName[5201:207] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** +[AppNameAppDelegate localizedDescription]: unrecognized selector sent to class 0xa79c'
2010-07-13 15:14:26.495 AppName[5201:207] Stack: (
    40911435,
    2569270537,
    41183227,
    40645910,
    40642578,
    9142,
    2815466,
    2819475,
    2844680,
    2826401,
    2858055,
    49271164,
    40452156,
    40448072,
    2817668,
    2850273,
    8776,
    8630
)

Does anyone have any suggestions as to what is going wrong? I already have some code set up to implement the "only on first launch" functionality, but have not included it here for clarity.

Thanks

Answer 1

   NSError *error;

You are declaring a local variable without initializing it. Therefore, it will be filled with garbage.

  [[NSFileManager defaultManager] copyItemAtPath:sourcePath 
                                        toPath:folderPath
                                         error:&error];

If no error occurs on this line, the garbage status of error would still remain.

  NSLog(@"Error description-%@ \n", [error localizedDescription]);

Now you send a message to some random, uninitialized location. This is the source of the crash.

---

To avoid this, initialize error to nil.

NSError* error = nil;
//             ^^^^^

Or print the error only when -copyItemAtPath:… returns NO (in which the error is correctly populated).

if (![[NSFileManager defaultManager] copyItemAtPath:sourcePath ...]) {
  NSLog(...); 
}