Question

I have a .plist created at the application launch with the following code (MyAppTableViewController):

NSArray *paths = NSSearchPathForDirectoriesInDomains (NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *finalPath = [documentsDirectory stringByAppendingPathComponent:@"Settings.plist"];

BOOL fileExists = [[NSFileManager defaultManager] fileExistsAtPath:finalPath];

if (!fileExists) {
    NSLog(@"Creating file");
    NSDictionary *plistDict = [[NSDictionary alloc]initWithObjectsAndKeys:@"1",@"Fade out",@"1",@"Enable Gestures",@"1",@"Proximity Sensor",@"1",@"Keep screen ON",nil];
    NSString *error = nil;

    NSData *plistData = [NSPropertyListSerialization dataFromPropertyList:plistDict format:NSPropertyListXMLFormat_v1_0 errorDescription:&error];

    if(plistDict) {
        [plistData writeToFile:finalPath atomically:YES];
    } else {
        NSLog(@"Error: %@", error);
        [error release];
    }
}

This works fine and the file is created with keys and values. I then have a table with four switches with a function toggle: as the selector.

The code inside -(void)toggle:(id)sender takes the switch’s value along with the row of the indexPath and modifies the plist accordingly:

-(void)toggle:(id)sender {
    UISwitch *aSwitch = (UISwitch *)sender;
    UITableViewCell *cell = (UITableViewCell *)aSwitch.superview;
    NSIndexPath *indexPath = [self.tableView indexPathForCell:cell];    

    NSArray *paths = NSSearchPathForDirectoriesInDomains (NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    NSString *finalPath = [documentsDirectory stringByAppendingPathComponent:@"Settings.plist"];
    NSMutableDictionary *dictionary = [NSMutableDictionary dictionaryWithContentsOfFile:finalPath];

    if (indexPath.section == 0 && indexPath.row == 0) {
        [dictionary setObject:[NSNumber numberWithBool:aSwitch.on] forKey:@"Fade out"];
    }
//There are further (similar) else if statements, but I'll leave them out.

    NSString *error = nil;
    NSData *plistData = [NSPropertyListSerialization dataFromPropertyList:dictionary format:NSPropertyListXMLFormat_v1_0 errorDescription:&error];

    if(dictionary) {
        [plistData writeToFile:finalPath atomically:YES];
    } else {
        NSLog(@"Error: %@", error);
        [error release];
    }
}

This is also working fine and modifies the plist successfully. My issue arises when I try to to retrieve the data with the following code:

NSArray *paths = NSSearchPathForDirectoriesInDomains (NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *finalPath = [documentsDirectory stringByAppendingPathComponent:@"Settings.plist"];
NSMutableDictionary *dictionary = [NSMutableDictionary dictionaryWithContentsOfFile:finalPath];

fadeOut = [[NSString stringWithFormat:[dictionary objectForKey:@"Fade out"]]boolValue];
proximitySensor = [[NSString stringWithFormat:[dictionary objectForKey:@"Proximity Sensor"]]boolValue];
enableGestures = [[NSString stringWithFormat:[dictionary objectForKey:@"Enable Gestures"]]boolValue];
keepScreenOn = [[NSString stringWithFormat:[dictionary objectForKey:@"Keep screen ON"]]boolValue];

In the declaration file, I have defined BOOL fadeOut,proximitySensor,enableGestures,keepScreenOn;. Grabbing the information works fine, but it’s when I change the BOOL values, the application crashes. I can’t quite understand what the problem is. Perhaps I’m missing the bigger picture or a simple but important mistake with Boolean values.

If I remove the above code, everything works fine. But If I leave it there, the app crashes with the following message:

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFBoolean length]: unrecognized selector sent to instance 0x3f39a9f0'

Help is much appreciated!

Answer 1

If you look at this line

fadeOut = [[NSString stringWithFormat:[dictionary objectForKey:@"Fade out"]]boolValue]

You’re initializing a string from an NSNumber (you stored you BOOL in a NSNumber). That’s invalid by itself.

If you need an bool value of an NSNumber, use simply boolValue on it.

fadeOut = [[dictionary objectForKey:@"Fade out"] boolValue];

That’s true for all the time you’re retrieving the boolean value.