a67559299a
* Update the template screen to use the new(ish) Observation framework. * Add a variant of deferFulfillment that supports observables. * Update snapshot fulfilment to work with either a publisher or a stream.
88 lines
3.9 KiB
Swift
88 lines
3.9 KiB
Swift
//
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// Copyright 2022-2024 New Vector Ltd.
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//
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// SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
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// Please see LICENSE files in the repository root for full details.
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//
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import Combine
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import Foundation
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/// A common ViewModel implementation for handling of `State` and `ViewAction`s. This original version
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/// is implemented using SwiftUI's original `ObservableObject` and `@Published` pattern.
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///
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/// Generic type State is constrained to the BindableState protocol in that it may contain (but doesn't have to)
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/// a specific portion of state that can be safely bound to.
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/// If we decide to add more features to our state management (like doing state processing off the main thread)
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/// we can do it in this centralised place.
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@MainActor
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class StateStoreViewModel<State: BindableState, ViewAction> {
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/// For storing subscription references.
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///
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/// Left as public for `ViewModel` implementations convenience.
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var cancellables = Set<AnyCancellable>()
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/// Constrained interface for passing to Views.
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var context: Context
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var state: State {
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get { context.viewState }
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set { context.viewState = newValue }
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}
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init(initialViewState: State, mediaProvider: MediaProviderProtocol? = nil) {
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context = Context(initialViewState: initialViewState, mediaProvider: mediaProvider)
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context.viewModel = self
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}
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/// Override to handles incoming `ViewAction`s from the `ViewModel`.
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/// - Parameter viewAction: The `ViewAction` to be processed in `ViewModel` implementation.
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func process(viewAction: ViewAction) {
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// Default implementation, -no-op
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}
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// MARK: - Context
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/// A constrained and concise interface for interacting with the ViewModel.
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///
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/// This class is closely bound to`StateStoreViewModel`. It provides the exact interface the view should need to interact
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/// ViewModel (as modelled on our previous template architecture with the addition of two-way binding):
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/// - The ability read/observe view state
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/// - The ability to send view events
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/// - The ability to bind state to a specific portion of the view state safely.
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/// This class was brought about a little bit by necessity. The most idiomatic way of interacting with SwiftUI is via `@Published`
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/// properties which which are property wrappers and therefore can't be defined within protocols.
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/// A similar approach is taken in libraries like [CombineFeedback](https://github.com/sergdort/CombineFeedback).
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/// It provides a nice layer of consistency and also safety. As we are not passing the `ViewModel` to the view directly, shortcuts/hacks
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/// can't be made into the `ViewModel`.
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@dynamicMemberLookup
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@MainActor
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final class Context: ObservableObject {
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fileprivate weak var viewModel: StateStoreViewModel?
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/// Get-able/Observable `Published` property for the `ViewState`
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@Published fileprivate(set) var viewState: State
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/// An optional image loading service so that views can manage themselves
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/// Intentionally non-generic so that it doesn't grow uncontrollably
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let mediaProvider: MediaProviderProtocol?
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/// Set-able/Bindable access to the bindable state.
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subscript<T>(dynamicMember keyPath: WritableKeyPath<State.BindStateType, T>) -> T {
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get { viewState.bindings[keyPath: keyPath] }
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set { viewState.bindings[keyPath: keyPath] = newValue }
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}
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/// Send a `ViewAction` to the `ViewModel` for processing.
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/// - Parameter viewAction: The `ViewAction` to send to the `ViewModel`.
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func send(viewAction: ViewAction) {
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viewModel?.process(viewAction: viewAction)
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}
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fileprivate init(initialViewState: State, mediaProvider: MediaProviderProtocol?) {
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self.viewState = initialViewState
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self.mediaProvider = mediaProvider
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}
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}
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}
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