Wpf.StateManagement

The State Management Protocol is a protocol used for state management using events. This protocol was presented at the talk below and ported to WPF by leveraging routed events. This implementation was mainly built to facilitate the use of the Flux pattern in WPF instead of the MVVM pattern. This implementation only provides the mechanisms to write to the store and should be used in conjunction with the Wpf.DependencyResolution protocol to expose the store to descendant elements.

This implementation provides extensions that can be used with elements to allow elements to store state and decouple side effects. When using this protocol, an implementation of the store must be provide through the IStore interface. This allows for extremely basic store implementation, as well as more complex implementation using observables, such as ReactiveX.

The use of this protocol assumes knowledge of Flux and/or any other implementations such as Elm and Redux.

Usage

1. Implement a store using the IStore interface.
2. Create routed events by extending the FluxAction class to request updates to the store.
3. Create reducers using the IReducer interface to update the store.
4. Call ProvideStore using the StoreProvider extension on the element to act as the orchestrator.
5. (Optional) Using Wpf.DependencyResolution, expose the store to descendants using the ProvideInstance method from the InstanceProvider extension.
6. (Optional) Call Enhance using the Enhancer extension on any descendant element to intercept, modify, or make side effecting calls. Enhancers are applied starting from the Enhancer farthest away from the StoreProvider in the element tree. As well, create any other routed events by extending FluxAction that may be required by the Enhancer.
7. Call Dispatch with routed events extending FluxAction.

API

IStore interface

State property

This getter provides the current state of the store.

Dispatch

This method should trigger the generation of new state. It should consequently trigger a property change on the State property.

IReducer interface

Reduce

This method is the implementation of the Reducer to provide the new state of the store.

FluxAction class

This class is a wrapper for RoutedEventArgs and is mainly used to identify routed events meant for State Management.

StoreProvider

ProvideStore

By calling ProvideStore with a IStore within an element, that element becomes a listener for any FluxActions and will dispatch those actions to the IStore. This is our bridge between the WPF event system and the store.

Enhancer

Enhance (AKA Middleware)

By calling Enhance with a DispatchHandler within an element, that element becomes a listener for any FluxActions and will execute the DispatchHandler. This is useful to executing side effecting code. In an ideal setup, all side effecting code should be isolated within services that collaborate with the Enhancer. This allows the Enhancer to be tested easily as a series of dispatches. Once again, Wpf.DependencyResolution can be used to inject services into the Enhancer.

Dispatcher

Dispatch

By calling Dispatch with any FluxAction within an element will trigger a store update at the StoreProvider. Any Enhancer in between the element and the StoreProvider can react to the dispatched FluxAction. Dispatch is basically a wrapper for the native RaiseEvent, but can be used to replace the event bus within the protocol if required.