Why NSMutableDictionary don't want write to file?

Question

- (void)viewDidLoad
{
    [super viewDidLoad];
    if ([[NSFileManager defaultManager] fileExistsAtPath:pathString]) 
    {
        infoDict = [[NSMutableDictionary alloc] initWithContentsOfFile:pathString];
    } 
    else 
    {
        infoDict = [[NSMutableDictionary alloc]initWithObjects:[NSArray arrayWithObjects:@"BeginFrame",@"EndFrame", nil] forKeys:[NSArray arrayWithObjects:[NSNumber numberWithBool:YES],[NSNumber numberWithBool:YES], nil]];
        if ([infoDict writeToFile:pathString atomically:YES])
        {
            NSLog(@"Created");
        } 
        else 
        {
            NSLog(@"Is not created");
            NSLog(@"Path %@",pathString);
        }
}

This is my code. I check if file is created, if not - I create a NSMutableDictionary and I write it to file at path, but writeToFile method returns NO. Where is problem? If I create this file with NSFileManager it works, but doesn't when I want to write a dictionary.

Peculation

Where does pathString come from? – Facial

I said with [[NSFileManager defaultManager] createFileAtPath:pathString contents:nil attributes:nil]; this file was create... – Peculation

i have first metode init and there I alloc it – Peculation

it seems like you made a mistake initalizing the infoDict. I mean objects should be keys and keys- objects. – Parnassus

Answer 1

writeToFile:atomically only works if the dictionary you call it on is a valid property list object (see docs).

For a NSDictionary to be a valid property list object, among other things, its keys must be strings, but in your example the keys are NSNumber instances.

Bowl

thx... this is problem... but it worked fine in 2011... without problems :D – Peculation

Thanks! I just got tripped up by the requirement that all the keys have to be strings. – Furrier

Answer 2

You can not control the content you are going to write sometimes. For example, you can't avoid a null value when you are going to write a JSON object that is gotten from a server.

NSData is compatible with these "invalid" values, so converting NSArray or NSDictionary to NSData is an ideal way in these cases.

write:

NSData *data = [NSKeyedArchiver archivedDataWithRootObject:jsonObject];
[data writeToFile:path atomically:YES];

read:

NSData *data = [NSData dataWithContentsOfFile:path];
NSDictionary *jsonObject = [NSKeyedUnarchiver unarchiveObjectWithData:data];

Garry

Awesome. As mentioned above you may not always be able to serialise JSON. This works great with my JSON. – Superannuation