Why NSMutableDictionary don't want write to file?

Question

- (void)viewDidLoad
{
    [super viewDidLoad];
    if ([[NSFileManager defaultManager] fileExistsAtPath:pathString]) 
    {
        infoDict = [[NSMutableDictionary          


        

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.

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];