iOS Swift - CLGeocoder completionHandler block

Question

I'm trying to parse a location (CLLocation) into a String.

    func locationToString (currentLocation: CLLocation) -> String? {
    var whatToReturn: String?
    CLGeocoder().reverseGeocodeLocation(currentLocation, completionHandler: { (placemarks: [AnyObject]!, error: NSError!) in
        if error == nil && placemarks.count > 0 {
            let location = placemarks[0] as CLPlacemark
            whatToReturn = "\(location.locality) \(location.thoroughfare) \(location.subThoroughfare)"

        }
    })
    return whatToReturn
}

Obviously, whatToReturn always returns null, because completionHandler runs in the background. I'm having a hard time understanding how do I update my String when completionHandler finishes?

Thanks.

What is your end goal with the string? This will have to be triggered somewhere in the completion block. — Logan, Jan 02 '15 at 23:34
I want to use the string (whatToReturn) and patse it into a textField. But, I'm not using this method from the controller itself, so I need a way to update the returned string... — EladB, Jan 02 '15 at 23:49
The best way to do that is probably to just set your textField's text within the completion block. [See Answer] — Logan, Jan 02 '15 at 23:52

Logan · Accepted Answer · 2015-01-03T00:02:00.600

If you want to use your string in a textField, like indicated in your comments, do this:

func getAndDisplayLocationStringForLocation(currentLocation: CLLocation) {
    CLGeocoder().reverseGeocodeLocation(currentLocation, completionHandler: { (placemarks: [AnyObject]!, error: NSError!) in
        if error == nil && placemarks.count > 0 {
            let location = placemarks[0] as CLPlacemark
            self.textField.text = "\(location.locality) \(location.thoroughfare) \(location.subThoroughfare)"

        }
    })
}

However, if you need access elsewhere, perhaps pass a closure as an arg:

func getAndDisplayLocationStringForLocation(currentLocation: CLLocation, withCompletion completion: (string: String?, error?, error: NSError?) -> ()) {
    CLGeocoder().reverseGeocodeLocation(currentLocation, completionHandler: { (placemarks: [AnyObject]!, error: NSError!) in
        if error == nil && placemarks.count > 0 {
            let location = placemarks[0] as CLPlacemark
            completion(string: "\(location.locality) \(location.thoroughfare) \(location.subThoroughfare)", error: nil)

        } else {
            completion(nil, error)
        }
    })
}

Then call like this:

yourModel.getAndDisplayLocationStringForLocation(someLocation) { (string: String?, error: NSError?) -> () in
    if (error == nil) {
        self.textField.text = string
    }
}

You may want to handle error etc. differently. This should be enough to get you started.

My bad, the error came of another part of my code. Thank you very much! Although, I have to ask, why was is built that way? I mean using reverseGeocodeLocation should be used from the model but completionHandler seems it was meant to be used from the controller. — EladB, Jan 03 '15 at 12:27
I can't speak for apple, but anytime there's a network operation required, the operation is backgrounded with a completion block to avoid blocking the UI for an indeterminate amount of time. — Logan, Jan 03 '15 at 14:34

iOS Swift - CLGeocoder completionHandler block

1 Answers1

Linked