public protocol ViewportState : AnyObject

ViewportState is a protocol that Viewport depends on as it orchestrates transitions to and from different states.

A ViewportState is a reference type and must not be shared among multiple Viewport instances simultaneously.

The observeDataSource(with:) method allows ViewportTransitions to consume a stream of camera updates from a target state while executing a transition. startUpdatingCamera() and stopUpdatingCamera() are invoked to tell the state that it should assume or relinquish control of the map’s camera. These are typically used by Viewport itself after a successful transition into a state and when exiting a state, respectively.

MapboxMaps provides implementations of ViewportState that can be created and configured via methods on Viewport. Applications may also define their own implementations to handle advanced use cases not covered by the provided implementations.

States should generally pre-warm their data sources as soon as they are created to minimize delays when they become current. For this reason, only states that are currently (or soon-to-be) needed should be kept alive so that unneeded resources (e.g. location services) can be released.

  • Registers a handler to receive the cameras being generated by this ViewportState.

    This method is commonly used by ViewportTransition implementations to obtain the target camera for transition animations. Transitions typically cannot start their animations until after handler is invoked for the first time, so it’s a good idea for states to invoke handler with the current camera if it’s not too stale rather than waiting for the next camera change to occur. To increase the likelihood that a valid camera exists when a handler is registered, design ViewportState implementations so that they start updating their internal state prior to when they are passed to transition(to:transition:completion:).

    The caller may either cancel the returned Cancelable or return false from handler to indicate that it wishes to stop receiving updates. Following either of these events, implemenations must no longer invoke handler and must release all strong references to it.



    func observeDataSource(with handler: @escaping (_ camera: CameraOptions) -> Bool) -> Cancelable



    A closure that is invoked by the state whenever its camera changes. Returns true to stay subscribed and false to unsubscribe. handler must be invoked on the main queue.


    The ViewportState‘s most recent camera.

    Return Value

    A Cancelable that the caller can use to unsubscribe.

  • Tells this state that it is now responsible for updating the camera.

    Viewport calls this method at the end of a successful transition into this state.

    Implementations typically have a dependency on either MapboxMap so that they can use its setCamera(to:) method to change the camea or on CameraAnimationsManager so that they can run camera animations.



    func startUpdatingCamera()
  • Tells this state that it is no longer responsible for updating the camera.

    Viewport calls this method at the beginning of the transition out of this state.

    Implementations must stop updating the camera immediately and should typically cancel any ongoing animations that they started when this method is invoked.



    func stopUpdatingCamera()