Resize UICollectionView Height

Question

I'm trying to resize a UICollectionView height by setting it to 0 when the view controller is loaded, then increasing its size with an animation when a button is pressed. I've tried a few different things but it doesn't change in size at all. Here's all the different things I've tried to change its height to 0:

CGRect bounds = [self.collectionView bounds];
[self.collectionView setBounds:CGRectMake(bounds.origin.x,
                                          bounds.origin.y,
                                          bounds.size.width,
                                          bounds.size.height - 100)];

....

CGRect frame = [self.collectionView frame];
[self.collectionView setFrame:CGRectMake(frame.origin.x,
                               frame.origin.y,
                               frame.size.width,
                               frame.size.height - 100)];

....

CGRect frame = self.collectionView.frame;
frame.size.height -= 100;
self.collectionView.frame = frame;

....

 self.collectionView.clipsToBounds = YES;
 self.collectionView.autoresizingMask = UIViewAutoresizingFlexibleHeight;

Hellenist

Is self.collectionView actually set to something? Are you using AutoLayout? – Hylomorphism

i set the collection view as a outlet. Yes AutoLayout is on. – Hellenist

If you're using AutoLayout then you're going to have to change the constraints rather than directly changing the frame. You'll want to set a height constraint on the collection view. – Hylomorphism

Ah ok, havent had much experience with AutoLayout. So what do i have to change, the Height constraint is set at 100 at the moment. – Hellenist

Then change it to 0, assuming you want it to be 0? Then switch it back to 100 when you want it back at 100 again. – Hylomorphism

I want it set as 0 when the ViewController loads, then when a button is pressed, it triggers a animation of the height increasing from 0 - 100, revealing to the CollectionView. – Hellenist

Re-reading your question I need to ask this - you realise that frame.size.height - 100 will take the current value and subtract 100, right? It sounds like perhaps you are thinking it means frame.size.height to 100. – Hylomorphism

Yeah, the code above is in viewDidLoad, so it sets the CollectionView height to zero, hence why i take away 100 from current height. When the user hits a button it + 100 to increase the height revealing the CollectionView to the user. The collection view holds a menu, i want this menu to be able to be hidden when not being used. – Hellenist

Ok good. Yep so if you're using AutoLayout then you need to change the layout constraint rather than setting the frame directly. – Hylomorphism

How do i do this programatically? – Hellenist

Answer 1

If you are using Interface Builder for UICollectionView initialisation, switch off "Use Autolayout" from the File Inspector in the xib file where the your CollectionView is created. Then you can change the height with setFrame or setBounds methods.

Treadle

It working fine but we will loose AutoLayout throughout the application. – Cupule

You could still use the autoResizing capabilities – Monaco

There is no way to achieve this with AutoLayout enabled? – Nagle

Answer 2

You can avoid disabling Autolayout by creating an outlet for the height constraint and then adjusting the constraint's constant in code.

Outlet

@IBOutlet weak var collectionViewVerticalConstraint: NSLayoutConstraint!

Adjustment

collectionViewVerticalConstraint.constant = 0

Martine