Merge pull request #1026 from liveview-native/optimize-view-bodies

Optimize updates with ObservableObject

Author: supernintendo

Sources/LiveViewNative/Property Wrappers/Attribute.swift

@@ -91,6 +91,8 @@ public struct Attribute<T>: DynamicProperty {
     private final class Storage: ObservableObject {
         var value: T?
         var previousValue: LiveViewNativeCore.Attribute?
+        
+        let objectWillChange = ObjectWillChangePublisher()
     }
 
     /// Before the View's body is produced, check if the attribute needs to be recomputed.

Sources/LiveViewNative/Property Wrappers/LiveContext.swift

@@ -50,7 +50,7 @@ public struct LiveContext<R: RootRegistry>: DynamicProperty {
     public func buildElement(_ element: ElementNode) -> some View {
         // can't use coordinator.builder.fromElement here, as it causes an infinitely recursive type when used with custom attributes
         // so use ElementView to break the cycle
-        return NodeView(node: element.node, context: storage)
+        return coordinator.builder.fromElement(element, context: storage)
     }
 
     /// Builds a view representing the children of the current element in the current context.

Sources/LiveViewNative/Property Wrappers/ObservedElement.swift

@@ -101,27 +101,33 @@ extension ObservedElement: DynamicProperty {
               let coordinator else {
             fatalError("Cannot use @ObservedElement on view that does not have an element and coordinator in the environment")
         }
-        self.observer.update(ref: nodeRef, children: coordinator.document[nodeRef].children().map(\.id), elementChanged: coordinator.elementChanged)
+        self.observer.update(
+            ref: nodeRef,
+            children: self.observer.observeChildren ? coordinator.document[nodeRef].children().map(\.id) : nil,
+            elementChanged: coordinator.elementChanged
+        )
     }
 }
 
 extension ObservedElement {
     private class Observer: ObservableObject {
         private var cancellable: AnyCancellable?
-        private var observeChildren = false
+        fileprivate var observeChildren = false
+        
+        let objectWillChange = ObjectWillChangePublisher()
 
         init(observeChildren: Bool) {
             self.observeChildren = observeChildren
         }
 
-        fileprivate func update(ref: NodeRef, children: [NodeRef], elementChanged: AnyPublisher<NodeRef, Never>) {
+        fileprivate func update(ref: NodeRef, children: [NodeRef]?, elementChanged: AnyPublisher<NodeRef, Never>) {
             if cancellable == nil {
                 cancellable = elementChanged
                     .filter { [weak self] in
                         if $0 == ref {
                             return true
                         } else if self?.observeChildren == true {
-                            return children.contains($0)
+                            return children?.contains($0) ?? false
                         } else {
                             return false
                         }

Sources/LiveViewNative/ViewTree.swift

@@ -30,7 +30,7 @@ struct ViewTreeBuilder<R: RootRegistry> {
     }
 
     @ViewBuilder
-    fileprivate func fromNode(_ node: Node, context: LiveContextStorage<R>) -> some View {
+    func fromNode(_ node: Node, context: LiveContextStorage<R>) -> some View {
         switch node.data {
         case .root:
             fatalError("ViewTreeBuilder.fromNode may not be called with the root node")
@@ -41,7 +41,7 @@ struct ViewTreeBuilder<R: RootRegistry> {
         }
     }
 
-    fileprivate func fromElement(_ element: ElementNode, context: LiveContextStorage<R>) -> some View {
+    func fromElement(_ element: ElementNode, context: LiveContextStorage<R>) -> some View {
         let view = createView(element, context: context)
 
         let modified = view.applyModifiers(R.self)
@@ -210,10 +210,17 @@ private struct ModifierApplicator<Parent: View, R: RootRegistry>: View {
     let context: LiveContextStorage<R>
 
     var body: some View {
-        let remaining = modifiers.dropFirst()
-        // force-unwrap is okay, this view is never constructed with an empty slice
-        parent.modifier(modifiers.first!.modifier)
-            .applyModifiers(remaining, element: element, context: context)
+        if modifiers.isEmpty {
+            parent
+        } else {
+            ModifierApplicator<_, R>(
+                // force-unwrap is okay, this view is never constructed with an empty slice
+                parent: parent.modifier(modifiers.first!.modifier),
+                modifiers: modifiers.dropFirst(),
+                element: element,
+                context: context
+            )
+        }
     }
 }
 
@@ -245,11 +252,7 @@ extension View {
 
     @ViewBuilder
     func applyModifiers<R: RootRegistry>(_ modifiers: ArraySlice<ModifierContainer<R>>, element: ElementNode, context: LiveContextStorage<R>) -> some View {
-        if modifiers.isEmpty {
-            self
-        } else {
-            ModifierApplicator(parent: self, modifiers: modifiers, element: element, context: context)
-        }
+        ModifierApplicator(parent: self, modifiers: modifiers, element: element, context: context)
     }
 
     @ViewBuilder
@@ -262,16 +265,6 @@ extension View {
     }
 }
 
-// not fileprivate because it's used by LiveContext.
-internal struct NodeView<R: RootRegistry>: View {
-    let node: Node
-    let context: LiveContextStorage<R>
-    
-    var body: some View {
-        context.coordinator.builder.fromNode(node, context: context)
-    }
-}
-
 private enum ForEachElement: Identifiable {
     case keyed(Node, id: String)
     case unkeyed(Node)
@@ -300,7 +293,7 @@ func forEach<R: CustomRegistry>(nodes: some Collection<Node>, context: LiveConte
         switch $0 {
         case let .keyed(node, _),
              let .unkeyed(node):
-            NodeView(node: node, context: context)
+            context.coordinator.builder.fromNode(node, context: context)
         }
     }
 }