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Vertical scrolling support #1

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Vertical scrolling support #1

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6aac568
Add support for .top snapping for vertical scrolling
lcarvajal May 12, 2021
e2841e5
Add support for center snap in vertical scrolling
lcarvajal May 12, 2021
ef4d878
Add support for bottom snapping on vertical scroll
lcarvajal May 12, 2021
20f0eb9
Add section on vertical scrolling to README
lcarvajal May 12, 2021
93ade53
Update comments describing scrolling logic
lcarvajal May 12, 2021
ba542b3
Add switch statement to return statement
lcarvajal May 13, 2021
16b9cd3
Remove horizontal from comment on scroll velocity
lcarvajal May 13, 2021
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11 changes: 11 additions & 0 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -143,6 +143,17 @@ snappingLayout.snapPosition = .right

![right](readmeImages/right.gif)

### Vertical scrolling

With vertical scrolling enabled, `.top`, `.center`, and `.bottom` can snap the cell to their respective parts of the collection view.

```swift
let snappingLayout = SnappingLayout()
snappingLayout.snapPosition = .top
```

![top](readmeImages/top.gif)

## 💬 Contributing
This is an open source project, so feel free to contribute. How?

Expand Down
140 changes: 105 additions & 35 deletions Sources/SnappingLayout/Classes/SnappingLayout.swift
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Expand Up @@ -13,14 +13,16 @@ public class SnappingLayout: UICollectionViewFlowLayout {
case left
case center
case right
case top
case bottom
}

// MARK: - Properties

/// Position to snap the cells.
public var snapPosition = SnapPositionType.center

/// Minimum horizontal velocity to trigger the snap effect.
/// Minimum velocity to trigger the snap effect.
private let minimumSnapVelocity: CGFloat = 0.3

// MARK: - UICollectionViewFlowLayout
Expand All @@ -29,52 +31,120 @@ public class SnappingLayout: UICollectionViewFlowLayout {
guard let collectionView = collectionView else {
return super.targetContentOffset(forProposedContentOffset: proposedContentOffset, withScrollingVelocity: velocity)
}

var offsetAdjusment = CGFloat.greatestFiniteMagnitude
let horizontalPosition: CGFloat

switch snapPosition {
case .left:
horizontalPosition = proposedContentOffset.x + collectionView.contentInset.left + sectionInset.left
case .center:
horizontalPosition = proposedContentOffset.x + (collectionView.bounds.width * 0.5)
case .right:
horizontalPosition = proposedContentOffset.x + collectionView.bounds.width - sectionInset.right
}

let targetRect = CGRect(x: proposedContentOffset.x, y: 0, width: collectionView.bounds.size.width, height: collectionView.bounds.size.height)
let layoutAttributesArray = super.layoutAttributesForElements(in: targetRect)
layoutAttributesArray?.forEach { layoutAttributes in
let itemHorizontalPosition: CGFloat

let verticalPosition: CGFloat

switch scrollDirection {
case .horizontal:
Comment on lines +38 to +39
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Instead of chaining 2 switch statements inside another switch, you can do it like this:

Suggested change
switch scrollDirection {
case .horizontal:
switch (scrollDirection, snapPosition) {
case (.horizontal, .left):
case (.horizontal, .center):
case (.horizontal, .right):
case (.vertical, .center):
case (.vertical, .top):
case (.vertical, .bottom):
case (.horizontal, .top), (.horizontal, .bottom), (.vertical, .left), (.vertical, .right):

switch snapPosition {
case .left:
itemHorizontalPosition = layoutAttributes.frame.minX - collectionView.contentInset.left
horizontalPosition = proposedContentOffset.x + collectionView.contentInset.left + sectionInset.left
verticalPosition = proposedContentOffset.y
case .center:
itemHorizontalPosition = layoutAttributes.center.x
horizontalPosition = proposedContentOffset.x + (collectionView.bounds.width * 0.5)
verticalPosition = proposedContentOffset.y
case .right:
itemHorizontalPosition = layoutAttributes.frame.maxX + collectionView.contentInset.right
horizontalPosition = proposedContentOffset.x + collectionView.bounds.width - sectionInset.right
verticalPosition = proposedContentOffset.y
case .top, .bottom:
horizontalPosition = proposedContentOffset.x
verticalPosition = proposedContentOffset.y
}

if abs(itemHorizontalPosition - horizontalPosition) < abs(offsetAdjusment) {
// If the drag velocity is lower than the minimum velocity (no matter the direction):
// snap the current cell to it's original position.
if abs(velocity.x) < self.minimumSnapVelocity {
offsetAdjusment = itemHorizontalPosition - horizontalPosition
case .vertical:
switch snapPosition {
case .left, .right:
horizontalPosition = proposedContentOffset.x
verticalPosition = proposedContentOffset.y
case .center:
horizontalPosition = proposedContentOffset.x
verticalPosition = proposedContentOffset.y + (collectionView.bounds.height * 0.5)
case .top:
horizontalPosition = proposedContentOffset.x
verticalPosition = proposedContentOffset.y + collectionView.bounds.height - sectionInset.top
case .bottom:
horizontalPosition = proposedContentOffset.x
verticalPosition = proposedContentOffset.y + collectionView.bounds.height - sectionInset.bottom
}
}

let targetRect = CGRect(x: proposedContentOffset.x, y: proposedContentOffset.y, width: collectionView.bounds.size.width, height: collectionView.bounds.size.height)
let layoutAttributesArray = super.layoutAttributesForElements(in: targetRect)
layoutAttributesArray?.forEach { layoutAttributes in

switch scrollDirection {
case .horizontal:
let itemHorizontalPosition: CGFloat

switch snapPosition {
case .left:
itemHorizontalPosition = layoutAttributes.frame.minX - collectionView.contentInset.left
case .center:
Comment on lines +75 to +82
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Same here.

itemHorizontalPosition = layoutAttributes.center.x
case .right:
itemHorizontalPosition = layoutAttributes.frame.maxX + collectionView.contentInset.right
case .top, .bottom:
itemHorizontalPosition = horizontalPosition
}

if abs(itemHorizontalPosition - horizontalPosition) < abs(offsetAdjusment) {
// If the drag velocity is lower than the minimum velocity (no matter the direction):
// snap the current cell to it's original position.
if abs(velocity.x) < self.minimumSnapVelocity {
offsetAdjusment = itemHorizontalPosition - horizontalPosition
}
// If the velocity is higher than the snap threshold and drag is right->left:
// move to the next cell on the right.
else if velocity.x > 0 {
offsetAdjusment = itemHorizontalPosition - horizontalPosition + (layoutAttributes.bounds.width + self.minimumLineSpacing)
}
// If the velocity is higher than the snap threshold and drag is left->right:
// move to the next cell on the left.
else { // velocity.x < 0
offsetAdjusment = itemHorizontalPosition - horizontalPosition - (layoutAttributes.bounds.width + self.minimumLineSpacing)
}
}
// If the velocity is higher than the snap threshold and drag is right->left:
// move to the next cell on the right.
else if velocity.x > 0 {
offsetAdjusment = itemHorizontalPosition - horizontalPosition + (layoutAttributes.bounds.width + self.minimumLineSpacing)
case .vertical:
let itemVerticalPosition: CGFloat

switch snapPosition {
case .left, .right:
itemVerticalPosition = verticalPosition
case .center:
itemVerticalPosition = layoutAttributes.center.y
case .top:
itemVerticalPosition = layoutAttributes.frame.minY - collectionView.contentInset.top
case .bottom:
itemVerticalPosition = layoutAttributes.frame.minY + collectionView.contentInset.bottom
}
// If the velocity is higher than the snap threshold and drag is left->right:
// move to the next cell on the left.
else { // velocity.x < 0
offsetAdjusment = itemHorizontalPosition - horizontalPosition - (layoutAttributes.bounds.width + self.minimumLineSpacing)

if abs(itemVerticalPosition - verticalPosition) < abs(offsetAdjusment) {
// If the drag velocity is lower than the minimum velocity (no matter the direction):
// snap the current cell to it's original position.
if abs(velocity.y) < self.minimumSnapVelocity {
offsetAdjusment = itemVerticalPosition - verticalPosition
}
// If the velocity is higher than the snap threshold and drag is bottom->top:
// move to the next cell on the bottom.
else if velocity.y > 0 {
offsetAdjusment = itemVerticalPosition - verticalPosition + (layoutAttributes.bounds.height + self.minimumLineSpacing)
}
// If the velocity is higher than the snap threshold and drag is top->bottom:
// move to the next cell on the top.
else { // velocity.x < 0
offsetAdjusment = itemVerticalPosition - verticalPosition - (layoutAttributes.bounds.height + self.minimumLineSpacing)
}
}
}


}

return CGPoint(x: proposedContentOffset.x + offsetAdjusment, y: proposedContentOffset.y)
switch scrollDirection {
case .horizontal:
return CGPoint(x: proposedContentOffset.x + offsetAdjusment, y: proposedContentOffset.y)
case .vertical:
return CGPoint(x: proposedContentOffset.x, y: proposedContentOffset.y + offsetAdjusment)
}
}
}