Hit Testing Behaviour

The behaviour of hit testing can be confusing at first. These rules define how hit testing usually behaves:

  1. Gesture callbacks in MapOptions are always invoked, no matter what is within the layers or the result of hitTests in those layers, with the exception of custom defined hit test behaviours (not those layers that support interactivity, see Layer Interactivity), such as applying GestureDetectors around Marker.children

GestureDetectors absorb hit tests, and so corresponding callbacks in MapOptions will not be invoked if they are defined/invoked in the GestureDetector.

Workarounds to resolve this are discussed below.

  1. Hit testing is always* performed on the interactable layers (see Layer Interactivity) even if they have not been set-up for interactivity: hit testing != interactivity

  2. Non-interactable layers (such as Overlay Image Layer) have no defined hitTest, and behaviour is situation dependent

  3. A successful hit test (true) from an interactable layer will prevent hit testing on layers below it in the children stack

To change this behviour, make use of these three widgets, wrapping them around layers when and as necessary:

  • TransulcentPointer: a general purpose 'widget' included with flutter_map that allows the child to hit test as normal, but also allows widgets beneath it to hit test as normal, both seperately

For example, a marker with a GestureDetector child that detects taps beneath a Polyline will not detect a tap, no matter if the PolylineLayer has a defined hitNotifier or the Polyline has a defined hitValue. A defined onTap callback in MapOptions would be called however. If the Marker were no longer obscured by the Polyline, it's onTap callback would be fired instead of the one defined in MapOptions.

However, this behaviour could be changed by wrapping the PolylineLayer with a TranslucentPointer. This would allow interacitivity to function as normal, but also allow the Marker beneath to have it's onTap callback fired. Further wrapping another TransclucentPointer around the MarkerLayer would allow all 3 detections to function.

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