Handle populating a tableview with asynchronous API calls - ios

Question

I have 2 objects. Note and User.
public class Note {
var userId: Int
var createdAtDate: NSDate
var content: String?
init(userId: Int, createdAtDate: NSDate) {
self.userId = userId
self.createdAtDate = createdAtDate
}
}
public class User {
var id: Int
var firstName: String
var lastName: String
var email: String
var avatar: UIImage?
init(id: Int, firstName: String, lastName: String, email: String) {
self.id = id
self.firstName = firstName
self.lastName = lastName
self.email = email
}
}
And there are two API methods. One to list out all the notes. This is the JSON response you get.
{
"status": "success",
"data": [
{
"user_id": 2,
"note": "This is a test\r\n\r\nThis is only a test.\r\n\r\nbeep boop",
"created_at": "2015-07-29 04:39:25"
}
]
}
Note that you only get the user's ID in this response. So to get the user details (first name ,last name etc), there's another API call. When you pass the user ID, it gives that user's details. This is its JSON response.
{
"status": "success",
"data": {
"id": 2,
"email": "dev#example.com",
"first_name": "John",
"last_name": "Appleseed",
"avatar": "avt.png"
}
}
Note that both these API methods return results asynchronously. Which brings me to my issue.
I need to display all these notes in a section-ed tableview with each note's user's full name in the footer.
The problem is since the user detail API call is asynchronous, so it happens in a different thread and it takes time to receive the results. But loading notes to the tableview happens separately so I can't figure out how to map each note's user when the user's detail arrives.
func tableView(tableView: UITableView, titleForFooterInSection section: Int) -> String? {
let note = notes[section]
APIClient.getUserDetails(id: id, success: { (data) -> Void in
}) { (error) -> Void in
}
return ""
}
For example, let's take the first note in the notes array. It gets the userId of that note and pass it to the getUserDetails method to retrieve the user details. But since this is async, the tableview won't wait until it receives that user's details. By the time you get that, it might have moved on to another note and spinning off async calls all over the place!
Anyone got an idea how to properly tackle this situation?

Answer 1

The approach to solve this might help you.
You could fire the second request (getUserDetails) in the success block of your first API call. (Or whichever method/delegate you would be using to handle receiving data from the server)
On success of the second request, you could simply reload your table to show the appropriate data
Since it takes time to show details you could add an activity indicator and hide the table till you receive all required data from the server.
I am assuming that you are using a separate block or delegate that would do the job of handling data response from the server.
If you strategically place your server requests on the success handling methods, one after the other, even though your data is interlinked and the calls are asynchronous - you get yourself a synchronous-like flow.
Hope that helps!