UICollectionView autosize height

问题:

How do I properly resize a UICollectionView so that it fully displays its contents? I have tried many things, including setting its frame, calling reloadData and invalidating the layout:

self.collectionView.contentSize = CGSizeMake(300, 2000);
self.collectionView.frame = CGRectMake(0, 0, 300, 2000);
[self.collectionView reloadData];
[self.collectionView.collectionViewLayout invalidateLayout];

but none of this has any effect. After pressing the button I still see the initial view, like this:

I have a small demo program where I have a data source producing 100 elements. In Interface Builder I initially set the size of the UICollectionView to a small value so that not all elements fit, after that I press a button after which the code above is executed. I expect the UICollectionView to now show all elements, but it doesn't.

EDIT: The demo program can be found at https://github.com/mjdemilliano/TestUICollectionView.

EDIT2: I have observed that the frame update is lost at some point, because if I press the button again, the current frame is back to the old value. After adding some log statements in the button event handler, the log output is:

before: frame = {{0, 58}, {320, 331}}, contentSize = {320, 1190}
update button pressed
after: frame = {{0, 0}, {300, 2000}}, contentSize = {300, 2000}
before: frame = {{0, 58}, {320, 331}}, contentSize = {320, 1190}
update button pressed
after: frame = {{0, 0}, {300, 2000}}, contentSize = {300, 2000}

I don't understand why the frame change is not kept, what is changing it.

At some point I will replace the hardcoded values by values obtained from the flow layout, but I wanted to rule that out and keep my example as simple as possible.

Context: What I want to do eventually is the following: I have a scrollable view with various controls like labels and images, and a collection view with dynamic content. I want to scroll all that, not just the collection view, therefore I am not using the collection view's own scrolling facilities, which work fine.

回答1:

I solved this eventually by fixing all Auto Layout issues, fixing the height of the collection view using a constraint. Then, whenever I know the content has changed I update the value of the constraint using the value collectionView.contentSize.height:

self.verticalLayoutConstraint.constant = self.collectionView.contentSize.height;

Then the collection view is resized properly and it behaves nicely within the overall scrollview. I have updated the GitHub test project with my changes.

To me, doing this by updating the constraint manually instead of being able to tell iOS: "make the frame height of the collection view as large as needed" does not feel right to me, but it's the best I have come up with so far. Please post a better answer if you have one.

回答2:

UICollectionViewFlowLayout *flowLayout;
flowLayout = [[UICollectionViewFlowLayout alloc]init];
[flowLayout setScrollDirection:UICollectionViewScrollDirectionVertical];
[flowLayout setMinimumInteritemSpacing:0.0f];
[flowLayout setMinimumLineSpacing:0.0f];
[self.collectionView setPagingEnabled:NO];
[flowLayout setItemSize:CGSizeMake(322.0, 148.0)];  //important to leave no white space between the images
[self.collectionView setCollectionViewLayout:flowLayout];

I found that autolayout in the storyboard is not helping too much. A correct setting for the UICollectionViewFlowLayout for your collectionView is the real help. If you adjust item size with setItemSize, you may get the result you want.

回答3:

Here's my implementation in Swift 3:

override func sizeThatFits(_ size: CGSize) -> CGSize {
    if (self.superview != nil) {
        self.superview?.layoutIfNeeded()
    }

    return collectionView.contentSize
}

回答4:

Here's a way to bind the CollectionView's height via it's intrinsic size. I used it to properly size a CollectionView inside a TableView Cell (with dynamic cells height). and it works perfectly.

First, add this to your UICollectionView subclass:

override var intrinsicContentSize: CGSize {
    get {
        return self.contentSize
    }
}

Then call layoutIfNeeded() after you reload data:

reloadData()
layoutIfNeeded()

回答5:

The simplest method I found is to pverride sizeThatFits: methods as is:

- (CGSize)sizeThatFits:(CGSize)size
{
    if( self.superview )
        [self.superview layoutIfNeeded]; // to force evaluate the real layout

    return self.collectionViewLayout.collectionViewContentSize;
}

回答6:

You can try out my custom AGCollectionView class

• Assign a height constraint of collectionView using a storyboard or programmatically.

- Assign this class to your UICollectionView.

class AGCollectionView: UICollectionView {

    fileprivate var heightConstraint: NSLayoutConstraint!

    override init(frame: CGRect, collectionViewLayout layout: UICollectionViewLayout) {
        super.init(frame: frame, collectionViewLayout: layout)
        self.associateConstraints()
    }

    required public init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        self.associateConstraints()
    }

    override open func layoutSubviews() {
        super.layoutSubviews()

        if self.heightConstraint != nil {
            self.heightConstraint.constant = floor(self.contentSize.height)
        }
        else{
            self.sizeToFit()
            print("Set a heightConstraint set size to fit content")
        }
    }

    func associateConstraints() {
        // iterate through height constraints and identify

        for constraint: NSLayoutConstraint in constraints {
            if constraint.firstAttribute == .height {
                if constraint.relation == .equal {
                    heightConstraint = constraint
                }
            }
        }
    }
}

回答7:

For me it is even simpler I think

-(UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath

{
//add following code line after adding cells, before Return
...........
.........
scrollView.contentSize = = collectionView.contentSize;

//now scrollView size is equal to collectionView size. No matter how small or big it is.

return cell;
}