Find markers shown in mapView

In MapKit:

I assume with Marker you mean an MKAnnotation. Instead of using the bounds of the mapView you should use the visibleMapRect and see if it contains the coordinates of the Marker in MKMapPoints. This is the code I used:

let markerPoint = MKMapPointForCoordinate(markers[0].coordinate)
if MKMapRectContainsPoint(mapView.visibleMapRect, markerPoint) {
    print("Found")
} else {
    print("Not found")
}

Only when the coordinates of the markers are visible (in other words, the marker is being displayed), this will print "Found". If off-screen, it will print "Not found".

Use the mapview's current projection. Use the projection's method called containsCoordinate to check if you marker's position is inside the projection, i.e. currently visible.

So something like:

let coord = marker.position
let isVisible = self.mapview.projection.containsCoordinate(coord)

https://developers.google.com/maps/documentation/ios-sdk/reference/interface_g_m_s_projection.html#aa6ad29e6831e40f00435c3aaeda8e08a