How to decode the Google Directions API polylines field into lat long points in Objective-C for iPhone?

Question

I want to draw routes on a map corresponding to directions JSON which I am getting through the Google Directions API: https://developers.google.com/maps/documentation/direct

Answer 1

If anybody else is trying to do this in swift, here's @RootCode's answer adapted to swift (2.3):

let path = GMSMutablePath()
let steps = directionsToShowOnMap.steps
for (idx, step) in steps.enumerate() {
    path.addCoordinate(coordinateFromJson(step["start_location"]))
    if let polylinePoints = step["polyline"].string, subpath = GMSPath(fromEncodedPath: polylinePoints) {
        for c in 0 ..< subpath.count() {
            path.addCoordinate(subpath.coordinateAtIndex(c))
        }   
    }
    if idx == steps.count - 1 {
        path.addCoordinate(coordinateFromJson(step["end_location"]))
    }
}
let polyline = GMSPolyline(path: path)
polyline.strokeColor = UIColor.blueColor()
polyline.strokeWidth = 3
polyline.map = mapView

and then:

private func coordinateFromJson(location: JSON) -> CLLocationCoordinate2D {
    return CLLocationCoordinate2DMake(location["lat"].double!, location["lng"].double!)
}