Previous/Next Functionality like iOS mail app? - ios

Question

I'm really close to figuring this out. So in the iOS mail app when you click on the two arrow keys it takes you to the previous/next mail. Its on the top right
I've managed to pass the indexPath value to my second viewcontroller and print in in the console. I can also increase and decrease from it.
if segue.identifier == "DetailVC" {
let detailVC = segue.destination as! DetailVC
let indexPath = self.collectionViewIBO.indexPathsForSelectedItems?.last!
detailVC.index = indexPath
}
EDIT
This is where I'm pulling the data from. It reads the values from my model. I cannot assign an indexPath to it however. I can only do that from the previous view controller
var monster: Monsters!
I've attempted to implement the "previous" functionality using this code. My view styling are in the displayDataForIndexPath() function and the function is called from my view will appear
#IBAction func monsPreviousIBO(_ sender: Any) {
self.index = IndexPath(row: self.index.row - 1, section: self.index.section)
displayDataForIndexPath()
}
But all it does is decrease the IndexPath. For some reason the data doesn't actually reload with my function. I'm missing some important puzzle piece here to achieving the same functionality.
EDIT The code in my displayDataForIndex is as follows
func displayDataForIndexPath() {
if index.row == 0 {
self.monsPreviousIBO.removeFromSuperview()
}
var monsterName = (String(format: "%03d", monster.speciesId!))
self.navigationItem.title = monster.name!
let gif = UIImage(gifName: monsterName)
self.gifIBO.setGifImage(gif, manager: gifManager)
gifIBO.contentMode = .center
guard monster.legendary! != true else {
// Value requirements not met, do something
monsterStatusLegend()
return
}
guard monster.subLegend! != true else {
// Value requirements not met, do something
monsterStatusSub()
return
}
guard monster.isMega! != true else {
// Value requirements not met, do something
monsterStatusMega()
return
}
}

Answer 1

you display all data depending on monster but you never change the monster depending which indexPath you used.
add some code to populate the monster from indexPath
monster = getMonster(index.row)
or in your case
#IBAction func monsPreviousIBO(_ sender: Any) {
self.index = IndexPath(row: self.index.row - 1, section: self.index.section)
monster = mons[self.index.row]
displayDataForIndexPath()
}
or better in the displayDataForIndexPath() add this line:
func displayDataForIndexPath() {
if index.row == 0 {
self.monsPreviousIBO.removeFromSuperview()
}
monster = mons[self.index.row]
//....
NOTE some suggestions:
i would change the line for the button then it is enabled if the indexpath gets >0:
self.monsPreviousIBO.isEnabled = (index.row != 0)
just save the row as monsterIndex = indexPath.row and then deal only with the index and not indexPath.
you don't need to save the current monster as monster if you use the monster only in displayDataForIndexPath - then you can get the current monster just there and have it a local variable in this function:
var monster = mons[self.index.row]