swift array not appending when in loop

Question

I'm trying to retrieve data from Parse to append to my array of Groups:

var displayedGroups = [Groups]()

Groups is a struct:

struct Groups{
    let name: String?
    let date: Date
    let number: Int
    let id: String

    init(id: String, name: String, date: Date, number: Int) {
        self.id = id
        self.name = name
        self.date = date
        self.number = number
    }
}

this is the function that I try to retrieve data with:

func getDisplayedGroups() {
        let query = PFQuery(className: "MeetUps")
        print(PFUser.current()?.username)
        query.whereKey("peeps", contains: PFUser.current()?.username)
        query.findObjectsInBackground { (objects, error) in
            if error != nil {
                print(error)
            } else if let objects = objects {
                for meetUps in objects {
                    let peeps = (meetUps["peeps"] as! [String])
                    let id = meetUps.objectId!
                    //let name = meetUps["meetUpName"] as? String
                    let date = meetUps["when"] as! Date
                    let group = Groups(id: id, name: " ", date: date, number: peeps.count)
                    print(group)
                    self.displayedGroups.append(group)
                }
            }
        }
        for i in displayedGroups {
            print(i)
        }
        tableView.reloadData()
    }

I've commented out let name = meetUps["meetUpName"]... because there are nil values in my parse dashboard's "meetUpName"-key column.

print(group) works and it prints a different group for every loop.

however, this block:

for i in displayedGroups {
                print(i)
            }

doesn't print at all :/ and as such my table isn't loading data from displayedGroups. has it got to do with asynchronous? shouldn't be right? since they are in the same block. I have no idea, please advise. Thanks!

Answer 1

findObjectsInBackground works asynchronously, put the loop and the line to reload the table view in the completion block.

You might need to reload the table view on the main thread.

...
    for meetUps in objects {
      let peeps = (meetUps["peeps"] as! [String])
      let id = meetUps.objectId!
      //let name = meetUps["meetUpName"] as? String
      let date = meetUps["when"] as! Date
      let group = Groups(id: id, name: " ", date: date, number: peeps.count)
      // print(group)
      self.displayedGroups.append(group)
    }
    for i in displayedGroups {
      print(i)
    }
    dispatch_async(dispatch_get_main_queue) {
       self.tableView.reloadData()
    }
...

Answer 2

From the code as the name suggests findObjectsInBackground runs in background ,that means it runs in different thread and not in main thread.So the below lines will be executed

for i in displayedGroups {
        print(i)
    }
    tableView.reloadData()

before finishing the background operation.

Kindly move the above code inside the completion block and don't forget to reloadData from main thread.

Edited function:

func getDisplayedGroups() {
let query = PFQuery(className: "MeetUps")
print(PFUser.current()?.username)
query.whereKey("peeps", contains: PFUser.current()?.username)

query.findObjectsInBackground { (objects, error) in
    if error != nil {
        print(error)
    } else if let objects = objects {
        for meetUps in objects {
            let peeps = (meetUps["peeps"] as! [String])
            let id = meetUps.objectId!
            //let name = meetUps["meetUpName"] as? String
            let date = meetUps["when"] as! Date
            let group = Groups(id: id, name: " ", date: date, number: peeps.count)
            print(group)
            self.displayedGroups.append(group)
        }
    }
    for i in self.displayedGroups {
        print(i)
    }
    dispatch_async(dispatch_get_main_queue()) {

    tableView.reloadData()
    }
}
}
}