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 director

Answer 1

I don't know a lot about iPhone programming or objective C, but out of curiosity, what is error in that case if the copy operation actually succeeded? Could it be the log lines that are crashing if there was no error?

[edit] Also, are you allowed to copy the entire contents of a subdirectory like that? (Again, I'm unfamiliar with the iOS API, just identifying possible sources of error based on what I know of other languages/APIs)

Answer 2

You log an error before you know that there is an error

put the code in an if-block

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

To describe your problem in more detail: the pointer of error points ANYWHERE and that object does not recognize that message. Therefore you get an exception

Answer 3

As a general programming practice, it's always best to initialize your variables with a default value:

NSError *error = nil;

In Objective-C, it is valid to send a message to nil. So, in your case, error variable would not cause a crash if it was initialized to nil.

For more info on the subject check Sending Messages to nil section at https://developer.apple.com/library/ios/#documentation/cocoa/conceptual/objectivec/Chapters/ocObjectsClasses.html

Answer 4

I just read through my code and found the issue. As Sean Edwards points out above, there is no error if it succeeds - hence the crash.

Here is my new code for those interested:

if([[NSFileManager defaultManager] copyItemAtPath:sourcePath toPath:folderPath error:&error]){
    NSLog(@"File successfully copied");
} else {
    NSLog(@"Error description-%@ \n", [error localizedDescription]);
    NSLog(@"Error reason-%@", [error localizedFailureReason]);
}

Answer 5

you should check whether the file already exists! Then copy.

+ (BOOL) getFileExistence: (NSString *) filename
{
    BOOL IsFileExists = NO;

    NSArray *documentPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDir = [documentPaths objectAtIndex:0];
    NSString *favsFilePath = [documentsDir stringByAppendingPathComponent:filename];

    NSFileManager *fileManager = [NSFileManager defaultManager];

    // Check if the database has already been created in the users filesystem
    if ([fileManager fileExistsAtPath:favsFilePath])
    {
        IsFileExists = YES;
    }
    return IsFileExists;
}

+ (NSString *)dataFilePath:(NSString *)filename {

    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *docDirectory = [paths objectAtIndex:0];
    return [docDirectory stringByAppendingPathComponent:filename];
}

- (void)copyFileToLocal:(NSString *)filename
{

    if (![AppDelegate getFileExistence:filename])
    {
        NSError *error;
        NSString *file = [[NSBundle mainBundle] pathForResource:filename ofType:nil];

        if (file)
        {
            if([[NSFileManager defaultManager] copyItemAtPath:file toPath:[AppDelegate dataFilePath:filename] error:&error]){
                NSLog(@"File successfully copied");
            } else {

                [[[UIAlertView alloc]initWithTitle:NSLocalizedString(@"error", nil) message: NSLocalizedString(@"failedcopydb", nil)  delegate:nil cancelButtonTitle:NSLocalizedString(@"ok", nil)  otherButtonTitles:nil] show];
                NSLog(@"Error description-%@ \n", [error localizedDescription]);
                NSLog(@"Error reason-%@", [error localizedFailureReason]);
            }
            file = nil;
        }
    }
}

NSLocalizedString are localize strings of the application.

Answer 6

   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(...); 
}