How to enable reordering a collection view in tvOS? - uicollectionview

Question

In iOS 9 all it takes to enable reordering a collection view is to implement moveItenAtIndexPath... like this...
override func collectionView(collectionView: UICollectionView,
moveItemAtIndexPath sourceIndexPath: NSIndexPath,
toIndexPath destinationIndexPath: NSIndexPath) {
print("sourceIndexPath= \(sourceIndexPath)")
print("destinationIndexPath= \(destinationIndexPath)")
}
But it doesn't seem to be enough in tvOS. What else needs to be implemented to enable reordering?
Here's the code from the view controller...
import UIKit
class ReorderableCollectionViewController: UICollectionViewController {
var numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]
override func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return numbers.count
}
override func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCellWithReuseIdentifier("CellReuseIdentifier", forIndexPath: indexPath) as! CustomCollectionViewCell
cell.backgroundColor = UIColor.yellowColor()
let number = numbers[indexPath.item]
cell.label.text = "\(number)"
return cell
}
override func collectionView(collectionView: UICollectionView,
moveItemAtIndexPath sourceIndexPath: NSIndexPath,
toIndexPath destinationIndexPath: NSIndexPath) {
print("sourceIndexPath= \(sourceIndexPath)")
print("destinationIndexPath= \(destinationIndexPath)")
}
override func didUpdateFocusInContext(context: UIFocusUpdateContext, withAnimationCoordinator coordinator: UIFocusAnimationCoordinator) {
print("didUpdateFocusInContext")
coordinator.addCoordinatedAnimations({
if let previousItem = context.previouslyFocusedView as? CustomCollectionViewCell {
previousItem.backgroundColor = UIColor.yellowColor()
}
if let nextItem = context.nextFocusedView as? CustomCollectionViewCell {
nextItem.backgroundColor = UIColor.redColor()
}
}, completion: nil)
}
}

Answer 1

I was unable to use built in methods to enable reordering of collectionview/tableview cells. However, there's always an option for a custom solution. In my current project I have concept of focused cell and highlighted cell. Also I have a separate button to trigger moving of highlighted cell. Also I wanted to have a behavior similar to home screen where long tap triggers moving too. Here are most of the code snippets required to achieve the result:
The class inherits from UIView and has UICollectionView connected to playlistCollection property.
Core idea: The view has special flag for reordering state. When this flag is triggered, all focus changes are blocked. If focus was about to move to another cell - swap currently focused cell with the one that user tried to focus. Otherwise don't do anything (so that focus never leaves collection view unless it's in normal state).
Other option: Instead of swapping cells around, you can also swap their data in the model and reload the cells. Advantages of this is that you can move selected cell through the list much faster (at the speed of scrolling through the list), but reloading 2 cells causes a slight lag, hence I decided to use my current solution. If you want to try this solution out the code triggering the cell change has to be moved from shouldUpdateFocusInContext to didUpdateFocusInContext and only focus changes moving outside of collectionview must be forbidden (rather than all focus changes).
Hope this helps.
_pressureGestureRecognizer overrides default behavior for all the remote buttons that are accessible to the app (menu, play/pause, tap), therefore it's only enabled when view is reordering state.
#implementation PlaylistView {
int _highlightedCell;
UILongPressGestureRecognizer *_longPressGestureRecognizer;
UITapGestureRecognizer *_pressGestureRecognizer;
BOOL _isBeingReordered;
NSMutableArray *_data;
}
#synthesize isBeingReordered = _isBeingReordered;
- (void)setup {
_isBeingReordered = NO;
_data = [[NSMutableArray alloc] initWithCapacity:20];
for (int i = 0; i < 20; i++)
{
[_data addObject:[NSString stringWithFormat:#"Temp %i", i]];
}
_longPressGestureRecognizer = [[UILongPressGestureRecognizer alloc] initWithTarget:self action:#selector(longPressed:)];
[self.playlistCollection addGestureRecognizer:_longPressGestureRecognizer];
_pressGestureRecognizer = [[UITapGestureRecognizer alloc] initWithTarget:self action:#selector(pressed:)];
_pressGestureRecognizer.allowedPressTypes = #[#(UIPressTypeMenu), #(UIPressTypeSelect), #(UIPressTypePlayPause)];
[self.playlistCollection addGestureRecognizer:_pressGestureRecognizer];
_pressGestureRecognizer.enabled = NO;
}
- (void)pressed:(UITapGestureRecognizer *)gesture {
if (!_isBeingReordered)
return;
_isBeingReordered = NO;
_pressGestureRecognizer.enabled = NO;
}
- (void)longPressed:(UILongPressGestureRecognizer *)gesture {
if (_isBeingReordered)
return;
_isBeingReordered = YES;
_pressGestureRecognizer.enabled = YES;
}
- (void)didUpdateFocusInContext:(UIFocusUpdateContext *)context withAnimationCoordinator:(UIFocusAnimationCoordinator *)coordinator {
[super didUpdateFocusInContext:context withAnimationCoordinator:coordinator];
if ([context.nextFocusedView isKindOfClass:[PlaylistCell class]]) {
if (_isBeingReordered)
{
NSLog(#"This should never happen.");
}
else
{
int nextIdx = [self.playlistCollection indexPathForCell:context.nextFocusedView].row;
if (nextIdx != _highlightedCell) {
PlaylistCell *prevCell = [self.playlistCollection cellForItemAtIndexPath:[NSIndexPath indexPathForItem:_highlightedCell inSection:0]];
if ([prevCell highlighted])
prevCell.highlighted = NO;
}
_highlightedCell = nextIdx;
}
}
}
- (void)moveCellFromRow:(int)artwork offset:(int)offset {
if (artwork + offset >= 0 && artwork + offset <= [_data count] - 1)
{
[self.playlistCollection performBatchUpdates:^{
[self.playlistCollection moveItemAtIndexPath:[NSIndexPath indexPathForItem:artwork inSection:0] toIndexPath:[NSIndexPath indexPathForItem:artwork + offset inSection:0]];
[self.playlistCollection moveItemAtIndexPath:[NSIndexPath indexPathForItem:artwork + offset inSection:0] toIndexPath:[NSIndexPath indexPathForItem:artwork inSection:0]];
_highlightedCell += offset;
//if there are certain elements in the cells that are position dependant, this is the right time to change them
//because these cells are not reloaded by default (for example you have idx displayed in your cell... the cells will swap but idxs won't by default)
} completion:^(BOOL finished) {
NSString *temp = _data[artwork + offset];
_data[artwork + offset] = _data[artwork];
_data[artwork] = temp;
}];
}
}
- (BOOL)collectionView:(UICollectionView *)collectionView shouldUpdateFocusInContext:(UICollectionViewFocusUpdateContext *)context {
if (_isBeingReordered)
{
//code only supports vertical reording.
if (context.focusHeading == UIFocusHeadingDown)
{
[self moveCellFromRow:_highlightedCell offset:1];
}
else if (context.focusHeading == UIFocusHeadingUp)
{
[self moveCellFromRow:_highlightedCell offset:-1];
}
return NO;
}
return YES;
}
- (BOOL)collectionView:(UICollectionView *)collectionView shouldHighlightItemAtIndexPath:(NSIndexPath *)indexPath {
//i have a custom code to handle highlights
return NO;
}
#end