How to Set the Collection View Cell Size Exactly Equal to the Collection View in iOS

How to increase the UICollectionview Cell Size equal to Screen Size in swift 4.2?

You need to change your cell size to fit the collectionview. Add this in viewDidLoad

if let flow = self.collectionView.collectionViewLayout as? UICollectionViewFlowLayout {
    flow.itemSize = self.collectionView.frame.size
}

how to set collection view cell as equal row cell for all screen

From the storyboard set CollectionViews Section Inset from size inspector as Top = 8, Bottom = 8, Left = 8 and Right = 8, it should look like as

And return size for cell as

- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath {

   //If you want your cell should be square in size the return the equal height and width, and make sure you deduct the Section Inset from it.
   return CGSizeMake((self.view.frame.size.width/3) - 16, (self.view.frame.size.width/3) - 45);
}

Thats it, Nothing more. You should see the result as mine:

How to change CollectionView cell width according to label text in swift

All items in your collectionView are taking the exact same size because you have specified layout.itemSize for your collectionView's flow layout

remove layout.itemSize = CGSize(width: self.collectionView.frame.size.width / 2, height: 80)

Other issues in code:

1. layout.invalidateLayout() is unnecessary in ViewDidLoad
2. if let layout = self.collectionView.collectionViewLayout as? UICollectionViewFlowLayout { to set minimumInteritemSpacing and minimumLineSpacing is unnecessary, in a statement just above it you have created let layout = UICollectionViewFlowLayout() why dont you simply set minimumInteritemSpacing and minimumLineSpacing there itself? Why use additional if let?

Simply write

        let layout = UICollectionViewFlowLayout()
        layout.scrollDirection = .horizontal
        layout.minimumInteritemSpacing = 0
        layout.minimumLineSpacing = 5
        self.collectionView.collectionViewLayout = layout

You need not specify item size, Collection view flow layout is set to be horizontal in nature, so by default each item will take the same height as the collection view height and if you have only one label inside the cell and if you have set autolayout constraint properly, label's intrinsic content size will ensure cell gets proper width

And forwhatever reason if you decide to wrap the label inside a UIView logic above holds good, as long as you set the label's autolayout constraint right, lablel's intrinsic content size will set the width of the containerView and which will in turn contribute to set the cell's width appropriately,

Here cell has background color of red, container view has orange and label has no background color, I have added leading and trailing spacing between cell and view as 10, and label and container view has leading and trailing space as 5

EDIT:

As OP is asking for constraints between container view, label and cell, I am updating answer to reflect the same

Clearly

  - - - - - - - - - - - - Cell - - - - - - - - - - - - - - - -
|       - - - - - - - - Container View - - - - - - - -          |
|     |                      |5                          |      |   
|-10- |-5-                  Label                     -5-| -10- |   
|     |                      |5                          |      |
|       - - - - - - - - - - - - - - - - - - - - - - - - -       |
|                                                               |
  - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  

You can add top and bottom constraint between cell and conatiner if you need, but I have kept container view vertically center to cell

How it works?

Label has intrinsic content-size which it gets from the text set to it, View does gets its intrinsic size based on the size of its subview, because there are no subviews in your container view, it gets its size from label and clearly whatever the size label returns view adds 10 to width and 10 to height ( 5 leading, 5 trailing, 5 top and 5 bottom) finally cell gets its size from its subviews, because there is only one subview (container view) it gets width from container view and for height it gets its height from collection view (as subviews dont provide enough data to calculate its height)

And if for some reason (might be because of some other constraints you have set knowingly / unknowingly like adding width constraint on container view) label is not taking its intrinsic content size correctly, you can always set setContentCompressionResistancePriority and setContentHuggingPriority on label to high in your cell's awake from nib

override func awakeFromNib() {
        super.awakeFromNib()
        self.label.setContentCompressionResistancePriority(.defaultLow, for: .horizontal)
        self.label.setContentHuggingPriority(.defaultHigh, for: .horizontal)
 }

Though this shouldnt be needed in usual case, if this is needed to get correct intrinsic size, there must be some other constraints which are preventing the label to take its proper implicit intrinsic content size, if I were in your position would rather check and fix it first. Nonetheless cant debug further with limited code you have provided.

EDIT 2:

Did not realize that OP is using custom instance of UICollectionViewFlowLayout and has not set estimatedItemSize property to automaticSize

        let layout = UICollectionViewFlowLayout()
        layout.scrollDirection = .horizontal
        layout.minimumInteritemSpacing = 0
        layout.minimumLineSpacing = 5
        layout.estimatedItemSize = UICollectionViewFlowLayout.automaticSize
        self.collectionView.collectionViewLayout = layout

How to dynamically size CollectionViewCell as per UILabel

You don't need to calculate the size of the strings that you want to display. Do the following:

1. Set collectionView's height equal to the expected height of tags.
2. Set tagLabel's leading, trailing, top and bottom constraints equal to the corresponding cell's contentView constraints.
3. Remove your implementation of func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize. The cell size will be calculated automatically if you don't use a custom value for estimatedItemSize. If you want to be sure, add (collectionView.collectionViewLayout as? UICollectionViewFlowLayout)?.estimatedItemSize = UICollectionViewFlowLayout.automaticSize to the function where you setup all views.

You will see the following result:

How to set UICollectionViewCell Width and Height programmatically

Use this method to set custom cell height width.

Make sure to add this protocols

UICollectionViewDelegate

UICollectionViewDataSource

UICollectionViewDelegateFlowLayout

If you are using swift 5 or xcode 11 and later you need to set Estimate Size to none using storyboard in order to make it work properly. If you will not set that than below code will not work as expected.

Swift 4 or Later

extension YourViewController: UICollectionViewDelegate {
    //Write Delegate Code Here
}

extension YourViewController: UICollectionViewDataSource {
    //Write DataSource Code Here
}

extension YourViewController: UICollectionViewDelegateFlowLayout {
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        return CGSize(width: screenWidth, height: screenWidth)
    }
}

Objective-C

@interface YourViewController : UIViewController<UICollectionViewDelegate,UICollectionViewDataSource,UICollectionViewDelegateFlowLayout>

- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath
{
    return CGSizeMake(CGRectGetWidth(collectionView.frame), (CGRectGetHeight(collectionView.frame)));
}

How to resize the collection view cells according to device screen size?

Implement sizeForItemAt method according to the view's frame size

Swift

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {

    let height = view.frame.size.height
    let width = view.frame.size.width
    // in case you you want the cell to be 40% of your controllers view
    return CGSize(width: width * 0.4, height: height * 0.4)
}

Objective C

- (CGSize)collectionView:(UICollectionView *)collectionView 
              layout:(UICollectionViewLayout *)collectionViewLayout 
   sizeForItemAtIndexPath:(NSIndexPath *)indexPath {

   CGFloat height = self.view.frame.size.height;
   CGFloat width  = self.view.frame.size.width;
   // in case you you want the cell to be 40% of your controllers view
   return CGSizeMake(width * 0.4, height * 0.4);
 }

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