iCloud Document Storage with UIDocument - Beginning iOS Cloud and Database Development - page 82

else
_data = [[CTData alloc] init];
}
return _data;
}
-(CTMetadata *)metadata {
if(_metadata == nil){
if(_fileWrapper != nil)
_metadata = [self decodeObjectFromWrapperWithKey:kMetadataKey];
else
_metadata = [[CTMetadata alloc] init];
}
return _metadata;
}
Both of these methods are identical except that we are working with CTData in one and CTMetadata in
the other. With that being said, let's just walk through the first one for CTD a ta.
When [self data] or self.data is called, this method will be called. It first checks to see whether
_data is equal to nil . If it isn't, then we just pass back our _data object. If it is nil, then we check to see
if our NSFileWrapper property has been set. If it has, we use it to call decodeObjectFromWrapperWithKey :
passing in our constant kDataKey . If it hasn't, we initialize a blank CTData object.
We can think of the process like this. When we first access a saved document, we have a file
wrapper. Therefore, we can decode it with that filewrapper, which in turn gives us our instantiated
CTData object. However, when we create a brand new document we have decoded anything so we
will create blank CTData and CTMetadata objects instead.
Now we need to add all our public access methods that we added in our interface.
-(NSString *)firstName {
return [self.data firstName];
}
-(void)setFirstName:(NSString *)firstName {
if([[self.data firstName] isEqualToString:firstName])
return;
NSString *oldFirstName = [self.data firstName];
[self.data setFirstName:firstName];
[self.undoManager setActionName:@"First Name Change"];
[self.undoManager registerUndoWithTarget:self selector:@selector(setFirstName:)
object:oldFirstName];
}
-(NSString *)lastName {
return [self.data lastName];
}