Lazy Loading Data in iOS Carplay

Question

How to lazy load the items while the user scrolling in Carplay ?

I am using beginLoadingChildItems from MPPlayableContentDataSource to load the first set of items but how I can call the next page when a user scrolls to the bottom of the page?

Answer 1

The way you can achieve this is inside the following function:

func beginLoadingChildItems(at indexPath: IndexPath, completionHandler: @escaping (Error?) -> Void)

As Example:

if (indexPath[componentIndex] + 1) % Threshold == 0 { // Threshold is Your Defined Batch Size

    // Load the next corresponding batch 

}

Load your lazy data, then call:

completionHandler(nil) // In case of no error has occurred

,but firstly, you need to return the total items count correctly in the following function:

func numberOfChildItems(at indexPath: IndexPath) -> Int

---

Something like the below,

class YourDataSource : MPPlayableContentDataSource {

    private var items = [MPContentItem]()
    private var currentBatch = 0

    func beginLoadingChildItems(at indexPath: IndexPath, completionHandler: @escaping (Error?) -> Void) {

        // indexPath[1]: is current list level, as per CarPlay list indexing (It's an array of the indices as ex: indexPath = [0,1] means Index 0 in the first level and index 1 at the second level).
        // % 8: Means each 8 items, I will perform the corresponding action.
       // currentBatch + 1 == nextBatch, This check in order to ensure that you load the batches in their sequences.

        let currentCount = indexPath[1] + 1

        let nextBatch = (currentCount / 8) + 1

        if currentCount % 8 == 0 && currentBatch + 1 == nextBatch { 

            // Load the next corresponding batch 
            YourAPIHandler.asyncCall { newItems in

                self.currentBatch = self.currentBatch + 1

                items.append(newItems)

                completionHandler(nil)

                MPPlayableContentManager.shared().reloadData()

            }

        } else {

            completionHandler(nil)

        }


    }

}

func numberOfChildItems(at indexPath: IndexPath) -> Int {

    return self.items.count

}

Answer 2

CarPlay does not support infinite scrolling by default. There is no callback when the last item on the list is displayed. However, the solution by @amr-el-sayed is an interesting one, since CarPlay will preload categories when they first appear on the screen. Thus, if the last item on the list is a category, CarPlay will call beginLoadingChildItemsAtIndexPath with the indexpath of the last item on the list, which could be used to simulate infinite scrolling. In that case, it becomes necessary to call MPPlayableContentManager reloadData because the preload is actually being called for the nested category (which is not displayed), rather than the category for which you are trying to implement infinite scrolling. This can result in some flash, as CarPlay must now redraw the entire UI. If possible, a better solution is simply to load a long list of items initially. Note that CarPlay will enforce a limit of enforcedContentItemsCount when MPPlayableContentManager.contentLimitsEnforced is true, for example, when a vehicle is in motion.