How do I duplicate UIViews from IB programmatically? - ios

Question

I need to add a UIView created in IB multiple times to a scrollView. Kind of like a TableView Cell. The code below only creates the View once. I could of course create the UIView programmatically and make it work, however that makes AutoLayout more difficult.
Question: How can I create a View with subview (eg ImageView, Labels etc) in StoryBoard and duplicate it in a scrollView?
class ScrollViewController: UIViewController {
#IBOutlet var backgroundView: UIView!
let scrollView = UIScrollView()
override func viewDidLoad() {
super.viewDidLoad()
let height = CGFloat(200.0)
self.scrollView.frame = self.view.bounds
//Make scrollView (height) = number of UIViews
self.scrollView.contentSize = CGSizeMake(self.view.bounds.size.width, height*2)
self.view.addSubview(self.scrollView)
var y = CGFloat(0.0)
for i in 0..<2 {
backgroundView.frame = CGRectMake(0, y, 20, 20)
self.scrollView.addSubview(backgroundView)
y += height
}
}

Answer 1

One way to do this is to put the view in its own XIB. In code, create a single instance of UINib and send it instantiateWithOwner:options: repeatedly. This is probably the simplest solution.
If you insist on using a storyboard, you can put the view under its own view controller. Then you can load multiple copies of both the view controller and the view using -[UIStoryboard instantiateViewControllerWithIdentifier:]. To do this properly, you'll need to learn about view controller containment.
Another approach is to serialize the view to an archive using +[NSKeyedArchiver archivedDataWithRootObject:]. Then you can deserialize the archiver repeatedly with +[NSKeyedUnarchiver unarchiveObjectWithData:]. However, if your view (or any of its descendant views) has a reference to some other object (like a model or controller object), you may end up duplicating a much larger object graph than you intended.
UPDATE
Let's say you created a custom subclass of UIView named MyView. Create a XIB by choosing File > New > File from the menu bar. In the dialog box, choose iOS > User Interface, then click the View icon. Name the XIB MyView.xib. Set the custom class of the view in the XIB to MyView. Lay out the subviews of MyView, set up constraints, and hook up the outlets of MyView to its subviews.
To load the XIB, you'll want to create an instance of UINib and then send it instantiateWithOwner:options: repeatedly. I would do it in a class method on MyView, like this:
#implementation MyView
static UINib *nib;
+ (instancetype)instantiate {
if (nib == 0) {
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(didReceiveMemoryWarning) name:UIApplicationDidReceiveMemoryWarningNotification object:nil];
NSString *myClassName = NSStringFromClass(self);
NSBundle *myClassBundle = [NSBundle bundleForClass:self];
nib = [UINib nibWithNibName:myClassName bundle:myClassBundle];
}
NSArray *topLevelObjects = [nib instantiateWithOwner:nil options:nil];
return [topLevelObjects firstObject];
}
+ (void)didReceiveMemoryWarning {
[[NSNotificationCenter defaultCenter] removeObserver:self name:UIApplicationDidReceiveMemoryWarningNotification object:nil];
nib = nil;
}
#end
Note that I've gone to some extra trouble here to discard the UINib object on a low-memory warning.
Anyway, to create an instance of MyView, you can just do this:
MyView *myView = [MyView instantiate];
That will create the UINib object if necessary, and then ask it to instantiate the view. Each call will return a new instance of MyView loaded from the XIB.