Question

I am starting to learn Objective-C and to help me doing so, I am using “Head First iPhone Development”. Now I am learning about SQLite databases and to get these to work I am told that the SQLite file needs to be in the Documents folder of the application and therefore I have to move the file.

I am using the example from the book but I can’t seem to get it to work. Everytime I compile it my app crashes. I have the following warning: “Incompatible Objective-C types initializing ‘struct NSURL *’, expected ‘struct NSString *’

Does anyone have a tip how to fix this?

EDIT:

The problem seems to be in these two lines with applicationDocumentsDirectory returning an NSURL but I tell it to return an NSString. I could tell it to return an NSURL but that gives me a problem on the next line where I use stringByAppendingPathComponent. Is there a way to fix this?

    NSString *documentsDirectory = [self applicationDocumentsDirectory];
    NSString *writableDBPath = [documentsDirectory stringByAppendingPathComponent:@"iBountyHunter.sqlite"];

This is what the Debugger Console outputs when the app crashes:

2011-02-04 07:33:42.126 iBountyHunter[591:207] -[NSURL stringByAppendingPathComponent:]: unrecognized selector sent to instance 0x6043f80
2011-02-04 07:33:42.128 iBountyHunter[591:207] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSURL stringByAppendingPathComponent:]: unrecognized selector sent to instance 0x6043f80'
*** Call stack at first throw:
(
    0   CoreFoundation                      0x00f87be9 __exceptionPreprocess + 185
    1   libobjc.A.dylib                     0x010dc5c2 objc_exception_throw + 47
    2   CoreFoundation                      0x00f896fb -[NSObject(NSObject) doesNotRecognizeSelector:] + 187
    3   CoreFoundation                      0x00ef9366 ___forwarding___ + 966
    4   CoreFoundation                      0x00ef8f22 _CF_forwarding_prep_0 + 50
    5   iBountyHunter                       0x00001d8e -[iBountyHunterAppDelegate createEditableCopyOfDatabaseIfNeeded] + 107
    6   iBountyHunter                       0x00001f24 -[iBountyHunterAppDelegate application:didFinishLaunchingWithOptions:] + 37
    7   UIKit                               0x002ba1fa -[UIApplication _callInitializationDelegatesForURL:payload:suspended:] + 1163
    8   UIKit                               0x002bc55e -[UIApplication _runWithURL:payload:launchOrientation:statusBarStyle:statusBarHidden:] + 439
    9   UIKit                               0x002c6db2 -[UIApplication handleEvent:withNewEvent:] + 1533
    10  UIKit                               0x002bf202 -[UIApplication sendEvent:] + 71
    11  UIKit                               0x002c4732 _UIApplicationHandleEvent + 7576
    12  GraphicsServices                    0x018bda36 PurpleEventCallback + 1550
    13  CoreFoundation                      0x00f69064 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 52
    14  CoreFoundation                      0x00ec96f7 __CFRunLoopDoSource1 + 215
    15  CoreFoundation                      0x00ec6983 __CFRunLoopRun + 979
    16  CoreFoundation                      0x00ec6240 CFRunLoopRunSpecific + 208
    17  CoreFoundation                      0x00ec6161 CFRunLoopRunInMode + 97
    18  UIKit                               0x002bbfa8 -[UIApplication _run] + 636
    19  UIKit                               0x002c842e UIApplicationMain + 1160
    20  iBountyHunter                       0x00001cf8 main + 102
    21  iBountyHunter                       0x00001c89 start + 53
)
terminate called after throwing an instance of 'NSException'

Answer 1

This will do the trick.

// Check the existence of database 
        NSFileManager *mngr = [[NSFileManager alloc] init];

        // If the database doesn't exist in our Document folder we copy it to Documents (this will be executed only the first time we launch the app).
        if (![mngr fileExistsAtPath:[NSString stringWithFormat:@"%@/Documents/db.sqlite", NSHomeDirectory()]]){
            NSString *filePath = [[NSBundle mainBundle] pathForResource:@"db.sqlite" ofType:nil];
            [mngr copyItemAtPath:filePath toPath:[NSString stringWithFormat:@"%@/Documents/db.sqlite", NSHomeDirectory()] error:NULL];
        }
        [mngr release];

here’s another version of the applicationDocumentsDirectory method:

+ (NSString*)applicationDocumentsDirectory {

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