public ValueProjectionObservable(StoreBase <TState> store, ValueProjector <TState, T> projector, Action onEmpty)
: base(onEmpty)
{
_store = store;
_projector = projector;
_currentValue = projector(_store.CurrentState);
}
/// <summary>
/// Send a value to all subscribers of a projection, simulating a change
/// to the store state.
/// </summary>
/// <param name="projector">
/// The projection function being simulated. The function is not called.
/// </param>
/// <param name="value">
/// The value to be sent to the project subscribers.
/// </param>
public void Publish <T>(ValueProjector <TState, T> projector, T value)
{
if (projector == null)
{
throw new ArgumentNullException(nameof(projector));
}
var observable = GetObservableForProjection <T>(projector);
observable?.PublishValue(value);
}
/// <summary>
/// Observe a projection of the application state for changes.
/// </summary>
/// <typeparam name="T">
/// The projector's return type.
/// </typeparam>
/// <param name="projector">
/// The projection function. Projections are pure static functions which receive
/// the current state and return a value based on that state.
/// </param>
/// <returns>
/// An <see cref="IObservable{T}"/> which can be subscribed for changes.
/// </returns>
public IProjectionObservable <T> Observe <T>(ValueProjector <TState, T> projector)
{
if (projector == null)
{
throw new ArgumentNullException(nameof(projector));
}
// if we've seen this projector before, reuse the observable we created for it, else create one
var observable = GetObservableForProjection <T>(projector);
if (observable == null)
{
observable = new ValueProjectionObservable <TState, T>(this, projector, () => ForgetProjection(projector));
_observables = _observables.Add(projector, (IStateListener <TState>)observable);
}
return(observable);
}
/// <summary>
/// Apply a projection function to the store and return its value immediately.
/// </summary>
/// <typeparam name="T">
/// The projector's return type.
/// </typeparam>
/// <param name="projector">
/// The projection function. Projections are pure static functions which receive
/// the current state and return a value based on that state.
/// </param>
/// <returns>
/// The value returned by the projection function.
/// </returns>
public T Project <T>(ValueProjector <TState, T> projector)
{
var value = projector(CurrentState);
return(value);
}