MockNotesDataSource.kt

    /**
     * Load the initial items
     */
    override fun loadInitial(params: LoadInitialParams<Int>, callback: LoadInitialCallback<Note>) {
        Log.d(TAG, "loadInitial: key=${params.requestedInitialKey ?: "undefined"}, size=${params.requestedLoadSize}")
        val pageSize = minOf(MAX_PAGE_SIZE, params.requestedLoadSize)
        val firstItem = inRange(params.requestedInitialKey ?: 0,0, items.size)
        val lastItem = inRange(firstItem + pageSize, 0, items.size)
        Log.d(TAG, "loadInitial: firstItem = $firstItem, lastItem = $lastItem")
        val data = if (firstItem == lastItem) emptyList<Note>() else items.subList(firstItem, lastItem)
        if (params.placeholdersEnabled) {
            callback.onResult(data, firstItem, items.size)
        } else {
            callback.onResult(data)
        }
    }

    /**
     * Load the next page
     */
    override fun loadAfter(params: LoadParams<Int>, callback: LoadCallback<Note>) {
        Log.d(TAG, "loadAfter: key=${params.key}, size=${params.requestedLoadSize}")
        val pageSize = minOf(MAX_PAGE_SIZE, params.requestedLoadSize)
        val firstItem = inRange(params.key + 1, 0, items.size)
        val lastItem = inRange(firstItem + pageSize, 0, items.size)
        Log.d(TAG, "loadAfter: firstItem = $firstItem, lastItem = $lastItem")
        val data = if (firstItem == lastItem) emptyList<Note>() else items.subList(firstItem, lastItem)
        callback.onResult(data)
    }

    /**
     * Load the previous page
     */
    override fun loadBefore(params: LoadParams<Int>, callback: LoadCallback<Note>) {
        Log.d(TAG, "loadAfter: key=${params.key}, size=${params.requestedLoadSize}")
        val pageSize = minOf(MAX_PAGE_SIZE, params.requestedLoadSize)
        val lastItem = inRange(params.key - 1, 0, items.size)
        val firstItem = inRange(lastItem - pageSize, 0, items.size)
        Log.d(TAG, "loadBefore: firstItem = $firstItem, lastItem = $lastItem")
        val data = if (firstItem == lastItem) emptyList<Note>() else items.subList(firstItem, lastItem)
        callback.onResult(data)
    }

    /**
     * Obtain an item based on the position
     */
    override fun getKey(item: Note): Int
            = items.indexOfFirst { it.noteId == item.noteId }