Paging Data in a UITableView - ios

Question

I am currently trying to create a UITableView that loads data as a user scrolls through it.
Basically, I have a data source with a lot of records. Way more than is feasible to load all at once. So I am querying 50 records at a time.
The problem lies in the fact that the user will be able to jump to the middle of this list via letters at the right. For example, if they press 'M' I load 50 records starting at 'M' into the list. Scrolling down will navigate through the M's and eventually the N's, O's, etc.
Of course, appending data to the bottom of the list is common and I was able to do this easily. I am having trouble finding reference or if it is done at all of appending 50 records to the top of the list as a user scrolls up.
For example, if the user hits 'M'. they should be able to scroll up and start seeing L's. I can append data to the beginning of the list, but the problem lies in the continuation of the scrolling list.
As of now, I can not get it working without a jump of the list or a complete stop.
Can anyone point me to someone who has done this cleanly?

Answer 1

OK, so I figured out the answer to my own question. Sorry for the post but maybe it will help someone else because I failed to find an exact solution to my answer else where, at least when it came to Swift.
First I loaded 50 records that started with 'M'. The JSON data would return the row number of these records. I created Int variables 'begin' and 'end' which held on to the range of rows I had loaded into my array. I set the numberOfRowsInSection to the 'end' of my range. This number was significantly more than the amount of rows I had loaded in my array, so I had to finagle how rows were loaded based on that array. Simple code snippet:
var begin:Int?
var end:Int = 0
func onDataLoad() {
data = data + DataHandler.data!
begin = data[0].Row
end = begin! + 50
tableView.reloadData()
let count = tableView.indexPathsForVisibleRows!.count - 2
let indexPath = NSIndexPath(forRow: begin! + count, inSection: 0)
tableView.scrollToRowAtIndexPath(indexPath, atScrollPosition: UITableViewScrollPosition.None, animated: false)
loading = false
}
func onBackwardData(evt:Event) {
data = DataHandler.data! + data
begin = begin! - 50
tableView.reloadData()
loading = false
}
func onForwardData() {
end = end + 50
data = data + DataHandler.data!
tableView.reloadData()
loading = false
}
override func numberOfSectionsInTableView(tableView: UITableView) -> Int {
return 1
}
override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return end
}
override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCellWithIdentifier("UserCell", forIndexPath: indexPath) as! PulseListTableViewCell
let cellrow = indexPath.row - begin!
if cellrow >= 0 {
cell.name.text = data[cellrow].Name
}
return cell
}
override func tableView(tableView: UITableView, willDisplayCell cell: UITableViewCell, forRowAtIndexPath indexPath: NSIndexPath) {
row = indexPath.row
let count = tableView.indexPathsForVisibleRows!.count + 5
if(indexPath.row >= end - 5 && !loading)
{
loading = true
DataHandler.getUsers(end)
}
else if(indexPath.row <= begin! + count && begin! > 0 && !loading)
{
loading = true
var offset = begin! - 50
if offset < 0 {
offset = 0
}
DataHandler.getUsers(offset)
}
}
This code is crude and has some hard coded things that would need to be adjusted to handle getting to the very beginning or end of the list but the idea is there. Sorry if this is a totally obvious solution/issue in the iOS world but I'm new and thought it might help.