How do I set collection view's cell size via the auto layout

Question

Hi I'm trying to resize the cell via the auto layout.

I want display the cell by the 3 by 3.

First Cell's margin left=0

Last Cell's margin right=0

And all of the cell's space has 1pt. Like an instagram.

Should I set to Cell's Size? I want set constraint via the Autolayout.

I also trying to set cell's size using the code.

Here is my code:

func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize {
    return CGSizeMake(123, 123);
}

func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumLineSpacingForSectionAtIndex section: Int) -> CGFloat {
    return 1;
}

func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumInteritemSpacingForSectionAtIndex section: Int) -> CGFloat {
    return 1;
}

But..I think it is not exactly calculate the cell's size.

How do I set cell's size depending on the screen's size?

I have to set space the 1pt between cell's.

Is there anyway to set only using the storyboard?

If not, How do I set by the code?

Thank you.

Answer 1

I don't believe you can set the size by only using the Storyboard because you can't set constraints to recurring items like collection view cells that are created on the fly at runtime.

You can easily compute the size from the information you are given. In collectionView(_:layout:sizeForItemAt:) you can access the bounds of the collectionView to compute the desired size of your cell:

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
    // Compute the dimension of a cell for an NxN layout with space S between
    // cells.  Take the collection view's width, subtract (N-1)*S points for
    // the spaces between the cells, and then divide by N to find the final
    // dimension for the cell's width and height.

    let cellsAcross: CGFloat = 3
    let spaceBetweenCells: CGFloat = 1
    let dim = (collectionView.bounds.width - (cellsAcross - 1) * spaceBetweenCells) / cellsAcross
    return CGSize(width: dim, height: dim)
}

Make sure your class adopts the protocol UICollectionViewDelegateFlowLayout.

This then works for iPhones and iPads of all sizes.