iosobjective-cuicollectionviewuikit-dynamics

Limiting vertical movement of UIAttachmentBehavior inside a UICollectionView

I have a horizontal UICollectionView with a custom UICollectionViewFlowLayout that has a UIAttachmentBehavior set on each cell to give it a bouncy feel when scrolling left and right. The behavior has the following properties:

attachmentBehavior.length = 1.0f;
attachmentBehavior.damping = 0.5f;
attachmentBehavior.frequency = 1.9f;

When a new cell is added to the collection view it's added at the bottom and then animated to its position also using a UIAttachmentBehavior. Naturally it bounces up and down a bit till it rests in its position. Everything is working as expected till now.

enter image description here

The problem I have starts appearing when the collection view is scrolled left or right before the newly added cell has come to rest. The adds left and right bounciness to the up and down one the cell already has from being added. This results in a very weird circular motion in the cell.

enter image description here

My question is, is it possible to stop the vertical motion of a UIAttachmentBehavior while the collection view is being scrolled? I've tried different approaches like using multiple attachment behaviors and disabling scrolling in the collection view till the newly added cell has come to rest, but non of them seem to stop this.

Solution

  • I've resorted to disabling scrolling in the collection view for a specific amount of time after a new cell is added, then removing the attachment behavior after that time has passed using its action property, then adding a new attachment behavior again immediately.

    That way I make sure the upwards animation stops before the collection view is scrolled left or right, but also the left/right bounciness is still there when scrolling.

    Certainly not the most elegant solution but it works.