Adding Click Event on InfoWindow/Marker in Google Maps SDK for native iOS/objective C

1.conform to the GMSMapViewDelegate protocol.

@interface YourViewController () <GMSMapViewDelegate>
// your properties
@end

2.set your mapView_ delegate.

mapView_.delegate = self;

3.implement the GMSMapViewDelegate method

- (void)mapView:(GMSMapView *)mapView didTapInfoWindowOfMarker:(GMSMarker *)marker {
    // your code
}

btw, marker.userData is useful. you can set your needed data into it and use it in - mapView:didTapInfoWindowOfMarker:

where you adding Map,add

 mapView_.delegate=self; 

then use this

-(void)mapView:(GMSMapView *)mapView
didTapInfoWindowOfMarker:(id<GMSMarker>)marker{

   //info window tapped

}

a full answer for swift 4

1. add GMSMapViewDelegate as delegate

2. set yourmap delegate like this : googlemap.delegate = self

3. add this func

func mapView(_ mapView: GMSMapView, didTap marker: GMSMarker) -> Bool 
            {
               // do something
                return true
            }