-(void)startNav{

if (nil != _polyLineMutable) {
    [_map removeOverlays:_polyLineMutable];
    [_polyLineMutable removeAllObjects];
}
[_addressField resignFirstResponder];
MKDirectionsRequest *request = [[MKDirectionsRequest alloc] init];
request.source = [MKMapItem mapItemForCurrentLocation];
CLGeocoder *geocoder = [[CLGeocoder alloc] init];
[geocoder geocodeAddressString:_addressField.text completionHandler:^(NSArray<clplacemark *=""> * _Nullable placemarks, NSError * _Nullable error) {

    if (placemarks.count == 0 || error) {
        return ;
    }
    CLPlacemark *clPm = placemarks.lastObject;
    MKPlacemark *pm = [[MKPlacemark alloc] initWithPlacemark:clPm];
    request.destination = [[MKMapItem alloc] initWithPlacemark:pm];
    MKDirections *direction = [[MKDirections alloc] initWithRequest:request];
    [direction calculateDirectionsWithCompletionHandler:^(MKDirectionsResponse * _Nullable response, NSError * _Nullable error) {
        for (MKRoute *route in response.routes) {
            for (MKRouteStep *step in route.steps) {
                NSLog(@"%@", step.instructions);
            }
            [_map addOverlay:route.polyline];
            [_polyLineMutable addObject:route.polyline];
        }
    }];
}];
}