How to determine height of UICollectionView with FlowLayout

Question

I've got an UICollectionView with an UICollectionViewFlowLayout, and i want to calculate its content size (for return in intrinsicContentSize needed for adjusting its height via AutoLayout).

The problems is: Even if I have a fixed and equal height for all cells, I don't know how many "rows"/lines I have in the UICollectionView. I also can't determine that count by the number of items in my data source, since the cells representing the data items vary in width, so does consequently the number of items I have in one line of the UICollectionView.

Since I couldn't find any hints on this topic in the official documentation and googling didn't bring me any further, any help and ideas would be appreciated very much.

Solution 1

Whoa! For some reason, after hours of research, I now found a pretty easy answer to my question: I was completely searching in the wrong place, digging through all the documentation I could find on UICollectionView.

The simple and easy solution lies in the underlying layout: Just call collectionViewContentSize on your myCollectionView.collectionViewLayout property and you get the height and width of the content as CGSize. It's as easy as that.

Solution 2

In case you are using Auto layout, then you could create a subclass of UICollectionView

If you use the below the code then you don't have to specify any height constraints for the collection view as it would vary based on the contents of the collection view.

Given below is the implementation:

@interface DynamicCollectionView : UICollectionView

@end

@implementation DynamicCollectionView

- (void) layoutSubviews
{
    [super layoutSubviews];

    if (!CGSizeEqualToSize(self.bounds.size, [self intrinsicContentSize]))
    {
        [self invalidateIntrinsicContentSize];
    }
}

- (CGSize)intrinsicContentSize
{
    CGSize intrinsicContentSize = self.contentSize;

    return intrinsicContentSize;
}

@end

Solution 3

At viewDidAppear you can get it by:

float height = self.myCollectionView.collectionViewLayout.collectionViewContentSize.height;

Maybe when you reload data then need to calculate a new height with new data then you can get it by: add observer to listen when your CollectionView finished reload data at viewdidload:

[self.myCollectionView addObserver:self forKeyPath:@"contentSize" options:NSKeyValueObservingOptionOld context:NULL];

Then add bellow function to get new height or do anything after collectionview finished reload:

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary  *)change context:(void *)context
{
    //Whatever you do here when the reloadData finished
    float newHeight = self.myCollectionView.collectionViewLayout.collectionViewContentSize.height;    
}

And don't forget to remove observer:

[self.myCollectionView removeObserver:self forKeyPath:@"contentSize" context:NULL];

Solution 4

Swift 3 code for user1046037 answer

import UIKit

class DynamicCollectionView: UICollectionView {

    override func layoutSubviews() {
        super.layoutSubviews()
        if !__CGSizeEqualToSize(bounds.size, self.intrinsicContentSize) {
            self.invalidateIntrinsicContentSize()
        }

    }

    override var intrinsicContentSize: CGSize {
        return contentSize
    }

}

Solution 5

user1046037 answer in Swift...

class DynamicCollectionView: UICollectionView {
    override func layoutSubviews() {
        super.layoutSubviews()
        if bounds.size != intrinsicContentSize() {
            invalidateIntrinsicContentSize()
        }
    }

    override func intrinsicContentSize() -> CGSize {
        return self.contentSize
    }
}

View more solutions

Comments

[Chris Chen]

whoa, I wish UITableView has something similar

[Chris Conover]

Ignatus, @jbandi, Chris et al, can you expand on this? When I tested with a horizontal scroll direction with a large inter-item spacing (so that the items would lay out horizontally), the collection view returned an invalid intrinsic content size (-1, -1), and collectionViewContentSize returned the what was effectively the bounds of the collection view - not taking into account that there was only one row surrounded by space. In short, it was not very intrinsic. Thanks!

[Georg]

didn't work for me... I am using my CollectionView inside a UITableViewCell and would like the tableview to grow in height as the collection view grows in height using iOS8 UITableViewAutomaticDimension But my collectionview stays small :(

[rounak]

What's the difference between collectionViewContentSize and contentSize of the scroll view?

[dotToString]

Awesome. Short and sweet solution to my UICollectionView inside of a UIScrollView!

[thesummersign]

@Georg, I am trying to do something similar. But when there is a deadlock. The collection view will get its layout information after cell loads on View and the cell loads after the height is calculated but the height need to be calculated from the collectionview. How did you fix this?

[Georg]

One important thing is to disable scrolling and scrollbars in the collection view

[Jun]

When you call contentSize of the collection view in viewDidLoad, it returns the frame of the collection view, collectionViewContentSize returns correct content size.

[xtrinch]

Same problem as Georg, it's about 50px in height when it should be more than 400

[Maverick1st]

@Georg i have exactly the same problem and haven't found a solution yet. Did you find one?

[Georg]

Yes, I set the collectionview to "not scrollabe, no scollbars" and then reload it then the content of the tableview is set. Also the collectionview is a subclass that returns it's content size as intrinsicContentSize. Hope that helps!

[user1046037]

IMHO it might be better to use the collection view without using the table view. If the flow layout doesn't meet your requirement you could create your own custom layout.

[DrMickeyLauer]

collectionViewContentSize only works on the 2nd (sometimes also 3rd) time for me, the first time it always returns a too large width (I have pinned the width, but care for a variable height), thus I have to force relayout at least once. Is there a better way?

[Abirami Bala]

Im a fresher, and Im not sure about where and how to use this in my ViewController, Can you please make an edit with the answer.....?

[Sebastian]

For me calling reloadData before querying the collectionViewContentSize size helped.

[May Phyu]

@MananDevani, could you please share your code or tutorial relating to this problem?. I have got such a problem right now. I don't know how to solve it. :(

[Manan Devani]

@May Phyu, Create outlet connection for UICollectionViewHeight and use following method. - (void)setCollectionViewHeight { self.collectionViewHeight.constant = self.collectionView.collectionViewLayout.collectionViewConte‌​ntSize.height; } // Call this method after loading the data.

[Mohammad Sadiq Shaikh]

just set this class to your collectionview in Storyboard

[Er. Vihar]

@ShikhaSharma: You can add the removeObserver code within "ViewDidDisappear" method, which will remove observer only after the view confirms that its disappeared. Please check the updated answer.

[Shikha Sharma]

am getting this error : An -observeValueForKeyPath:ofObject:change:context: message was received but not handled.

[Er. Vihar]

@ShikhaSharma: Sorry, It's my mistake to specify the method. Try to put removeobserver code in viewWillDisappear.

[Chen Li Yong]

@ChrisChen TableView actually does have something similar, and even more easier. Just call myTableView.contentSize and you'll get the content size as CGSize!

[Rahul K Rajan]

I found that its not working in iPhone 6/7 plus and XR,XS-MAX

[Ajay Kumar]

This saved me, Thanks!

[KolaCaine]

It's work perfectly but If you have something like UILabel above, the content from collectionView pass over other element above, do you have another solution ?

[asanli]

For whom it can help: I had to do a "layoutIfNeeded()" before this so I could get it working.

[ArielSD]

When is collectionViewContentSize set? When can we read from it?

[SinisterMJ]

Just made use of this and it worked pretty well - it had the advantage of informing my callback before the screen actually displayed to the user, so that I was able to adjust a critical constraint size based on the final size of the UICollectionView being rendered.