Question

I want to write some values to an external file and use NSDictionary for this purpose:

NSString *s = @"123456";
NSString *key = @"key";
NSString *file = pathInAppDirectory(@"values");
NSDictionary *dic = [NSDictionary dictionaryWithObject:s forKey:key];
[dic writeToFile:file atomically:YES];

Ok, pathInAppDirectory looks like this:

NSString *pathInAppDirectory(NSString *fileName)
{
    NSArray *documentDirectories = NSSearchPathForDirectoriesInDomains(NSApplicationDirectory, NSUserDomainMask, YES); 

    NSString *appDir = [documentDirectories objectAtIndex:0];
    return [appDir stringByAppendingPathComponent:fileName];
}

What happens is exactly nothing: If I want to have look in the file somewhat later and want to display the values, null is returned. And a look into the folder of the iPhone simulator shows an empty folder, too. What happens there or, to be more specific: what does not happen?

Answer 1

You need to use NSDocumentDirectory instead of NSApplicationDirectory. It is not possible to write in the Application bundle.

Cleaned up example:

- (NSString *)pathInAppDirectory:(NSString *)fileName {
    NSArray *documentDirectories = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); 

    NSString *appDir = [documentDirectories objectAtIndex:0];
    return [appDir stringByAppendingPathComponent:fileName];
}

    NSString *s = @"123456";
    NSString *key = @"key";
    NSDictionary *dic = [NSDictionary dictionaryWithObject:s forKey:key];
    NSString *filePath = [self pathInAppDirectory:@"values"];
    [dic writeToFile:filePath atomically:YES];