Question

This is my first question here. I have a notepad app that you can draw on, change pen size, change colors, etc.

The drawing is done in core-graphics code in the view’s drawRect: method after detecting the touches. Now I want to be able to save this drawing to Core Data or a text file doesn’t matter and be able to load it again and keep drawing. Can I save it as NSDATA with imagePngRepresentation? It is bitmap then and I can’t keep drawing again.

Please help me what is the best way to do this, to save the drawing and then be able to load it up again to be able to continue drawing?

Thanks a lot!!

Answer 1

I know this is late, but I spent the past few hours figuring this out myself. So here goes:

In nib/xib files (and now, storyboards), you can ‘freeze dry’ your views in a file by constructing your interface in Interface Builder. Essentially, what it is doing here is archiving these objects and storing them in a file. Wouldn’t it be great if users could do this to views in your app? Well, they can!

Apple’s guide on archiving really helped. I read it from front to back.

For each UIView subclass you have, implement encodeWithCoder:

- (void)encodeWithCoder:(NSCoder *)aCoder
{
    [super encodeWithCoder:aCoder];

    // Encode any objects you want to load later. 
    // For example: [aCoder encodeObject:colors forKey:@"colors"];
    // Make sure they conform to the NSCoder protocol!
}

Just a note about this: some objects do not conform to the NSCoder protocol. For instance, I use UIGestureRecognizer objects in some of my UIView subclasses. Since they don’t conform to the protocol, I just recreate them when the view is unarchived with initWithCoder:. So make sure you have a way of retrieving objects that you can’t archive!

In initWithCoder:

- (void)initWithCoder:(NSCoder *)aDecoder
{
    self = [super initWithCoder:aDecoder];
    if (self) {
        // Initialize your view
        // Restore any objects that you encoded
        // For example: self.colors = [aDecoder decodeObjectForKey:@"colors"];
    }
    return self;
}

To save the view:

- (NSString *)applicationDocumentsDirectory {
    return [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
}

- (IBAction)tapSave:(id)sender {
    NSString *directory = [self applicationDocumentsDirectory];
    NSString *archivePath = [directory stringByAppendingPathComponent:@"<filename>.archive"];
    BOOL result = [NSKeyedArchiver archiveRootObject:<your root view> toFile:archivePath];
}

Finally, to load the view and its subviews:

- (IBAction)tapLoad:(id)sender {
    NSString *directory = [self applicationDocumentsDirectory];
    NSString *archivePath = [NSTemporaryDirectory() stringByAppendingPathComponent:@"<filename>.archive"];
    unarchivedView = [NSKeyedUnarchiver unarchiveObjectWithFile:archivePath];
}

Hope this helps!