The Composable Architecture

Co-authored-by: Stephen Celis <stephen.celis@gmail.com>

Sources/ComposableArchitecture/SwiftUI/WithViewStore.swift

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+import Combine
+import SwiftUI
+
+/// A structure that transforms a store into an observable view store in order to compute views from
+/// store state.
+///
+/// Due to a bug in SwiftUI, there are times that use of this view can interfere with some core
+/// views provided by SwiftUI. The known problematic views are:
+///
+/// * If a `GeometryReader` is used inside a `WithViewStore` it will not receive state updates
+///   correctly. To work around you either need to reorder the views so that `GeometryReader`
+///   wraps the `WithViewStore`, or, if that is not possible, then you must hold onto an explicit
+///   `@ObservedObject var viewStore: ViewStore<State, Action>` in your view in lieu of using
+///   this helper (see [here](https://gist.github.com/mbrandonw/cc5da3d487bcf7c4f21c27019a440d18)).
+/// * If you create a `Stepper` via the `Stepper.init(onIncrement:onDecrement:label:)` initializer
+///   inside a `WithViewStore` it will behave erratically. To work around you should use the
+///   initializer that takes a binding (see
+///   [here](https://gist.github.com/mbrandonw/dee2ceac2c316a1619cfdf1dc7945f66)).
+public struct WithViewStore<State, Action, Content>: View where Content: View {
+  private let content: (ViewStore<State, Action>) -> Content
+  private var prefix: String?
+  @ObservedObject private var viewStore: ViewStore<State, Action>
+
+  /// Initializes a structure that transforms a store into an observable view store in order to
+  /// compute views from store state.
+
+  /// - Parameters:
+  ///   - store: A store.
+  ///   - isDuplicate: A function to determine when two `State` values are equal. When values are
+  ///     equal, repeat view computations are removed,
+  ///   - content: A function that can generate content from a view store.
+  public init(
+    _ store: Store<State, Action>,
+    removeDuplicates isDuplicate: @escaping (State, State) -> Bool,
+    @ViewBuilder content: @escaping (ViewStore<State, Action>) -> Content
+  ) {
+    self.content = content
+    self.viewStore = ViewStore(store, removeDuplicates: isDuplicate)
+  }
+
+  public var body: some View {
+    if let prefix = self.prefix {
+      print(
+        """
+        \(prefix.isEmpty ? "" : "\(prefix): ")\
+        Evaluating WithViewStore<\(State.self), \(Action.self), ...>.body
+        """
+      )
+    }
+    return self.content(self.viewStore)
+  }
+
+  /// Prints debug information to the console whenever the view is computed.
+  ///
+  /// - Parameter prefix: A string with which to prefix all debug messages.
+  /// - Returns: A structure that prints debug messages for all computations.
+  public func debug(prefix: String = "") -> Self {
+    var view = self
+    view.prefix = prefix
+    return view
+  }
+}
+
+extension WithViewStore where State: Equatable {
+  /// Initializes a structure that transforms a store into an observable view store in order to
+  /// compute views from equatable store state.
+  ///
+  /// - Parameters:
+  ///   - store: A store of equatable state.
+  ///   - content: A function that can generate content from a view store.
+  public init(
+    _ store: Store<State, Action>,
+    @ViewBuilder content: @escaping (ViewStore<State, Action>) -> Content
+  ) {
+    self.init(store, removeDuplicates: ==, content: content)
+  }
+}
+
+extension WithViewStore: DynamicViewContent where State: Collection, Content: DynamicViewContent {
+  public typealias Data = State
+
+  public var data: State {
+    self.viewStore.state
+  }
+}