/// <summary>
/// Transition into the specified state.
/// </summary>
/// <param name="id">StateId of the new state.</param>
public void EnterState(StateId id)
{
EngineState state = _gameStates[id];
if (state == null)
{
throw new InvalidOperationException("Attempting to switch to state id '" + id + "' which has a null state instance!");
}
if (_currentState != null)
{
_currentState.OnExit();
}
_currentState = state;
_currentState.OnEnter();
}