uicollection view load more data at bottom scroll. iOS Swift

i want to load more data in collection view when i scroll bottom to the collection view. i did not found any library for swift language. can anyone please tell me how can i do this? question1 -> how to load more data when i scroll down question2 -> if i will able to get more data on scrolling to the bottom so how should i add in same mutable array. so it load whole data.