Waiting for geocoding loop to complete - ios

Question

So I understand that geocoding in iOS is an asynchronous method, and right now I'm working on an app that accesses a list of address from Parse (for restaurants) and performs forward geocoding on each address. Ideally I'd like this operation to be performed before a table is populated after a couple days of struggles this is just not happening for me.
My question is how do I get an iteration of forward geocoding to be completed prior to anything else happening in my app?
I've trying looking into grand central dispatch methods and I tried following this tutorial but I have got no luck:
http://www.raywenderlich.com/79150/grand-central-dispatch-tutorial-swift-part-2
Here is my code:
As you will see I'm trying to put found CLLocations in
var storeDict:NSDictionary = [CLLocation:PFObject]()
override func queryForTable() -> PFQuery! {
var query:PFQuery = PFQuery(className: self.parseClassName)
query.whereKey("Food", equalTo: foodName)
var prices = query.findObjects()
var i = 0
println(prices.count)
let geoCoder = CLGeocoder()
for price in prices {
var location:String = price.objectForKey("Address") as String
geoCoder.geocodeAddressString(location, completionHandler:
{(placemarks: [AnyObject]!, error: NSError!) in
if error != nil {
println("Geocode failed with error: \(error.localizedDescription)")
} else if placemarks.count > 0 {
var placemark = placemarks[0] as CLPlacemark
var location = placemark.location
var coordinateLocation:CLLocation = CLLocation(latitude: location.coordinate.latitude, longitude: location.coordinate.longitude) as CLLocation
print(price)
print(coordinateLocation)
self.Restaurant[coordinateLocation] = price as? PFObject
print(i)
i++
}
})
println("check")
}
return query
}

Answer 1

First, you might want to notify the user that they can't do anything in the app until the data has finished being loaded (and geocoded). You could add a semi-transparent view with a spinning wheel over it to prevent the user from interacting with the app.
The table should have absolutely no idea where you are in the process -- whether you've started geocoding, finished geocoding, or how long ago you ran the geocoding. It should have no idea whether you even queried to get the restaurants. All it knows is its datasource, and if that datasource has objects, then it will use it to populate the rows in the table.
Say the datasource is an array of Restaurant objects. If the array is empty, then the table will be empty. You can do KVO on the array, so that whenever the datasource is updated, reloadData will be called on the tableView.
Now you've separated out the table as a separate problem that you've handled. Not onto querying and geocoding.
Currently, you're not querying Parse in background with block, but you're literally halting the program until the query finishes. I understand why you're electing to do that since you're concerned about doing nothing until the query finishes, but it would be a lot better to execute in background.
Once the query finishes, you loop through the resulting objects and geocode one by one. Just a word of caution, Apple does not allow you to geocode a ton of objects at a time -- they will throttle you, so I would limit the query to only return the amount of objects you need. When an object is finished being geocoded, add it to the datasource. This will trigger the reload of the table, and your data will appear.
Say now that you queried 20 objects. Each time the geocoding completes, your tableview will be reloaded. It might be better to wait until the geocoding completes on all 20 objects before calling reload. You can actually add each geocode operation onto a queue with each operation adding their geocoded object to some temporary array, and then add an operation that updates your datasource with the temporary array. At that moment, the table will be updated with the new data. Note that the downside of doing it this way is that some addresses might take longer the geocode than others, so rather than displaying whatever data it was able to geocode thus far, it will wait until everything has been fully geocoded.
Lastly, you could have the query run in background and have the geocoding occur in its completion block. If the view just loaded for the first time, it can show the spinning wheel until the datasource is updated. When the datasource is updated, the spinning wheel is removed.