Drawing Route Between Two Places on GMSMapView in iOS

`first get all points coordinates which are coming in route then add these points latitude and longitude in path in will draw path according to that`


GMSCameraPosition *cameraPosition=[GMSCameraPosition cameraWithLatitude:18.5203 longitude:73.8567 zoom:12];
_mapView =[GMSMapView mapWithFrame:CGRectZero camera:cameraPosition];
_mapView.myLocationEnabled=YES;
GMSMarker *marker=[[GMSMarker alloc]init];
marker.position=CLLocationCoordinate2DMake(18.5203, 73.8567);
marker.icon=[UIImage imageNamed:@"aaa.png"] ;
marker.groundAnchor=CGPointMake(0.5,0.5);
marker.map=_mapView;
GMSMutablePath *path = [GMSMutablePath path];   
[path addCoordinate:CLLocationCoordinate2DMake(@(18.520).doubleValue,@(73.856).doubleValue)];
[path addCoordinate:CLLocationCoordinate2DMake(@(16.7).doubleValue,@(73.8567).doubleValue)];

GMSPolyline *rectangle = [GMSPolyline polylineWithPath:path];
rectangle.strokeWidth = 2.f;
rectangle.map = _mapView;
self.view=_mapView;

I've written the following code which should do the trick for you:

- (void)drawRoute
{
    [self fetchPolylineWithOrigin:myOrigin destination:myDestination completionHandler:^(GMSPolyline *polyline)
     {
         if(polyline)
             polyline.map = self.myMap;
     }];
}

- (void)fetchPolylineWithOrigin:(CLLocation *)origin destination:(CLLocation *)destination completionHandler:(void (^)(GMSPolyline *))completionHandler
{
    NSString *originString = [NSString stringWithFormat:@"%f,%f", origin.coordinate.latitude, origin.coordinate.longitude];
    NSString *destinationString = [NSString stringWithFormat:@"%f,%f", destination.coordinate.latitude, destination.coordinate.longitude];
    NSString *directionsAPI = @"https://maps.googleapis.com/maps/api/directions/json?";
    NSString *directionsUrlString = [NSString stringWithFormat:@"%@&origin=%@&destination=%@&mode=driving", directionsAPI, originString, destinationString];
    NSURL *directionsUrl = [NSURL URLWithString:directionsUrlString];


    NSURLSessionDataTask *fetchDirectionsTask = [[NSURLSession sharedSession] dataTaskWithURL:directionsUrl completionHandler:
         ^(NSData *data, NSURLResponse *response, NSError *error)
         {
             NSDictionary *json = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:&error];
             if(error)
             {
                 if(completionHandler)
                     completionHandler(nil);
                 return;
             }

             NSArray *routesArray = [json objectForKey:@"routes"];

             GMSPolyline *polyline = nil;
             if ([routesArray count] > 0)
             {
                 NSDictionary *routeDict = [routesArray objectAtIndex:0];
                 NSDictionary *routeOverviewPolyline = [routeDict objectForKey:@"overview_polyline"];
                 NSString *points = [routeOverviewPolyline objectForKey:@"points"];
                 GMSPath *path = [GMSPath pathFromEncodedPath:points];
                 polyline = [GMSPolyline polylineWithPath:path];
             }

             // run completionHandler on main thread                                           
             dispatch_sync(dispatch_get_main_queue(), ^{
                 if(completionHandler)
                      completionHandler(polyline);
             });
         }];
    [fetchDirectionsTask resume];
}

If anyone is looking for a Swift 3.0 for @Tarek's answer, you can use this. This also use Alamofire and SwiftyJSON.

func drawPath()
{
    let origin = "\(currentLocation.latitude),\(currentLocation.longitude)"
    let destination = "\(destinationLoc.latitude),\(destinationLoc.longitude)"


    let url = "https://maps.googleapis.com/maps/api/directions/json?origin=\(origin)&destination=\(destination)&mode=driving&key=YOURKEY"

    Alamofire.request(url).responseJSON { response in
      print(response.request)  // original URL request
      print(response.response) // HTTP URL response
      print(response.data)     // server data
      print(response.result)   // result of response serialization

      let json = JSON(data: response.data!)
      let routes = json["routes"].arrayValue

      for route in routes
      {
        let routeOverviewPolyline = route["overview_polyline"].dictionary
        let points = routeOverviewPolyline?["points"]?.stringValue
        let path = GMSPath.init(fromEncodedPath: points!)
        let polyline = GMSPolyline.init(path: path)
        polyline.map = self.mapView
      }
    }
  }

For swift 3 to draw polyline

func getPolylineRoute(from source: CLLocationCoordinate2D, to destination: CLLocationCoordinate2D){

        let config = URLSessionConfiguration.default
        let session = URLSession(configuration: config)

        let url = URL(string: "https://maps.googleapis.com/maps/api/directions/json?origin=\(source.latitude),\(source.longitude)&destination=\(destination.latitude),\(destination.longitude)&sensor=true&mode=driving&key=YOURKEY")!

        let task = session.dataTask(with: url, completionHandler: {
            (data, response, error) in
            if error != nil {
                print(error!.localizedDescription)
                self.activityIndicator.stopAnimating()
            }
            else {
                do {
                    if let json : [String:Any] = try JSONSerialization.jsonObject(with: data!, options: .allowFragments) as? [String: Any]{

                        guard let routes = json["routes"] as? NSArray else {
                            DispatchQueue.main.async {
                                self.activityIndicator.stopAnimating()
                            }
                            return
                        }

                        if (routes.count > 0) {
                            let overview_polyline = routes[0] as? NSDictionary
                            let dictPolyline = overview_polyline?["overview_polyline"] as? NSDictionary

                            let points = dictPolyline?.object(forKey: "points") as? String

                            self.showPath(polyStr: points!)

                            DispatchQueue.main.async {
                                self.activityIndicator.stopAnimating()

                                let bounds = GMSCoordinateBounds(coordinate: source, coordinate: destination)
                                let update = GMSCameraUpdate.fit(bounds, with: UIEdgeInsetsMake(170, 30, 30, 30))
                                self.mapView!.moveCamera(update)
                            }
                        }
                        else {
                            DispatchQueue.main.async {
                                self.activityIndicator.stopAnimating()
                            }
                        }
                    }
                }
                catch {
                    print("error in JSONSerialization")
                    DispatchQueue.main.async {
                        self.activityIndicator.stopAnimating()
                    }
                }
            }
        })
        task.resume()
    }

    func showPath(polyStr :String){
        let path = GMSPath(fromEncodedPath: polyStr)
        let polyline = GMSPolyline(path: path)
        polyline.strokeWidth = 3.0
        polyline.strokeColor = UIColor.red
        polyline.map = mapView // Your map view
    }

Note : You need to put googleDirection API key in URL.