Mvu component

src/Fabulous/Builders.fs

@@ -1,6 +1,7 @@
 namespace Fabulous
 
 open System.ComponentModel
+open Fabulous.WidgetAttributeDefinitions
 open Fabulous.WidgetCollectionAttributeDefinitions
 open Fabulous.StackAllocatedCollections
 open Fabulous.StackAllocatedCollections.StackList
@@ -217,3 +218,51 @@ type AttributeCollectionBuilder<'msg, 'marker, 'itemMarker> =
 
             res
     end
+
+type SingleChildBuilderStep<'msg, 'marker> = delegate of unit -> WidgetBuilder<'msg, 'marker>
+
+[<Struct>]
+type SingleChildBuilder<'msg, 'marker, 'childMarker> =
+    val WidgetKey: WidgetKey
+    val Attr: WidgetAttributeDefinition
+    val AttributesBundle: AttributesBundle
+
+    new(widgetKey: WidgetKey, attr: WidgetAttributeDefinition) =
+        { WidgetKey = widgetKey
+          Attr = attr
+          AttributesBundle = AttributesBundle(StackList.empty(), ValueNone, ValueNone) }
+
+    new(widgetKey: WidgetKey, attr: WidgetAttributeDefinition, attributesBundle: AttributesBundle) =
+        { WidgetKey = widgetKey
+          Attr = attr
+          AttributesBundle = attributesBundle }
+
+    member inline this.Yield(widget: WidgetBuilder<'msg, 'childMarker>) =
+        SingleChildBuilderStep(fun () -> widget)
+
+    member inline this.Combine
+        (
+            [<InlineIfLambda>] a: SingleChildBuilderStep<'msg, 'childMarker>,
+            [<InlineIfLambda>] _b: SingleChildBuilderStep<'msg, 'childMarker>
+        ) =
+        SingleChildBuilderStep(fun () ->
+            // We only want one child, so we ignore the second one
+            a.Invoke())
+
+    member inline this.Delay([<InlineIfLambda>] fn: unit -> SingleChildBuilderStep<'msg, 'childMarker>) =
+        SingleChildBuilderStep(fun () -> fn().Invoke())
+
+    member inline this.Run([<InlineIfLambda>] result: SingleChildBuilderStep<'msg, 'childMarker>) =
+        let childAttr = this.Attr.WithValue(result.Invoke().Compile())
+        let struct (scalars, widgets, widgetCollections) = this.AttributesBundle
+
+        WidgetBuilder<'msg, 'marker>(
+            this.WidgetKey,
+            AttributesBundle(
+                scalars,
+                (match widgets with
+                 | ValueNone -> ValueSome [| childAttr |]
+                 | ValueSome widgets -> ValueSome(Array.appendOne childAttr widgets)),
+                widgetCollections
+            )
+        )

src/Fabulous/Component/Binding.fs

@@ -54,7 +54,7 @@ type BindingExtensions =
         (
             _: ComponentBuilder,
             [<InlineIfLambda>] request: Binding<'T>,
-            [<InlineIfLambda>] continuation: BindingValue<'T> -> ComponentBodyBuilder<'msg, 'marker>
+            [<InlineIfLambda>] continuation: BindingValue<'T> -> ComponentBodyBuilder<'marker>
         ) =
         // Despite its name, ComponentBinding actual value is not stored in this component, but in the source component
         // So, we do not need to increment the number of bindings here

src/Fabulous/Component/Builder.fs

@@ -2,15 +2,14 @@ namespace Fabulous
 
 /// Delegate used by the ComponentBuilder to compose a component body
 /// It will be aggressively inlined by the compiler leaving no overhead, only a pure function that returns a WidgetBuilder
-type ComponentBodyBuilder<'msg, 'marker> =
-    delegate of bindings: int<binding> * context: ComponentContext -> struct (int<binding> * WidgetBuilder<'msg, 'marker>)
+type ComponentBodyBuilder<'marker> = delegate of bindings: int<binding> * context: ComponentContext -> struct (int<binding> * WidgetBuilder<unit, 'marker>)
 
 type ComponentBuilder() =
-    member inline this.Yield(widgetBuilder: WidgetBuilder<'msg, 'marker>) =
-        ComponentBodyBuilder<'msg, 'marker>(fun bindings ctx -> struct (bindings, widgetBuilder))
+    member inline this.Yield(widgetBuilder: WidgetBuilder<unit, 'marker>) =
+        ComponentBodyBuilder<'marker>(fun bindings ctx -> struct (bindings, widgetBuilder))
 
-    member inline this.Combine([<InlineIfLambda>] a: ComponentBodyBuilder<'msg, 'marker>, [<InlineIfLambda>] b: ComponentBodyBuilder<'msg, 'marker>) =
-        ComponentBodyBuilder<'msg, 'marker>(fun bindings ctx ->
+    member inline this.Combine([<InlineIfLambda>] a: ComponentBodyBuilder<'marker>, [<InlineIfLambda>] b: ComponentBodyBuilder<'marker>) =
+        ComponentBodyBuilder<'marker>(fun bindings ctx ->
             let struct (bindingsA, _) = a.Invoke(bindings, ctx) // discard the previous widget in the chain but we still need to count the bindings
             let struct (bindingsB, resultB) = b.Invoke(bindings, ctx)
 
@@ -19,15 +18,15 @@ type ComponentBuilder() =
 
             struct (resultBindings, resultB))
 
-    member inline this.Delay([<InlineIfLambda>] fn: unit -> ComponentBodyBuilder<'msg, 'marker>) =
-        ComponentBodyBuilder<'msg, 'marker>(fun bindings ctx ->
+    member inline this.Delay([<InlineIfLambda>] fn: unit -> ComponentBodyBuilder<'marker>) =
+        ComponentBodyBuilder<'marker>(fun bindings ctx ->
             let sub = fn()
             sub.Invoke(bindings, ctx))
 
-    member inline this.Run([<InlineIfLambda>] body: ComponentBodyBuilder<'msg, 'marker>) =
+    member inline this.Run([<InlineIfLambda>] body: ComponentBodyBuilder<'marker>) =
         let compiledBody =
             ComponentBody(fun ctx ->
                 let struct (_, result) = body.Invoke(0<binding>, ctx)
                 struct (ctx, result.Compile()))
 
-        WidgetBuilder<'msg, 'marker>(Component.WidgetKey, Component.Body.WithValue(compiledBody))
+        WidgetBuilder<unit, 'marker>(ComponentWidget.WidgetKey, Component.Body.WithValue(compiledBody))

src/Fabulous/Component/Component.fs

@@ -205,37 +205,67 @@ avatar1.Background <- Blue
 
 type ComponentBody = delegate of ComponentContext -> struct (ComponentContext * Widget)
 
-type Component(treeContext: ViewTreeContext, body: ComponentBody, context: ComponentContext) =
-    let mutable _body = body
-    let mutable _context = context
-    let mutable _widget = Unchecked.defaultof<_>
-    let mutable _view = null
-    let mutable _contextSubscription: IDisposable = null
+type IBaseComponent =
+    inherit IDisposable
 
+type IComponent =
+    inherit IBaseComponent
+    abstract member SetBody: ComponentBody -> unit
+    abstract member SetContext: ComponentContext -> unit
+
+module Component =
     // TODO: This is a big code smell. We should not do this but I can't think of a better way to do it right now.
     // The implementation of this method is set by the consuming project: Fabulous.XamarinForms, Fabulous.Maui, Fabulous.Avalonia
-    static let mutable _setAttachedComponent: obj -> Component -> unit =
+    let mutable setAttachedComponent: obj -> IBaseComponent -> unit =
         fun _ _ -> failwith "Please call Component.SetComponentFunctions() before using Component"
 
-    static let mutable _getAttachedComponent: obj -> Component =
+    let mutable getAttachedComponent: obj -> IBaseComponent =
         fun _ -> failwith "Please call Component.SetComponentFunctions() before using Component"
 
-    static member SetComponentFunctions(get: obj -> Component, set: obj -> Component -> unit) =
-        _getAttachedComponent <- get
-        _setAttachedComponent <- set
+    let setComponentFunctions (get: obj -> IBaseComponent, set: obj -> IBaseComponent -> unit) =
+        getAttachedComponent <- get
+        setAttachedComponent <- set
 
-    static member GetAttachedComponent(view: obj) = _getAttachedComponent view
-    static member SetAttachedComponent(view: obj, comp: Component) = _setAttachedComponent view comp
+    /// TODO: This is actually broken. On every call of the parent, the body will be reassigned to the Component triggering a re-render because of the noCompare.
+    /// This is not what was expected. The body should actually be invalidated based on its context.
+    let Body =
+        Attributes.defineSimpleScalar "Component_Body" ScalarAttributeComparers.noCompare (fun _ currOpt node ->
+            let target = getAttachedComponent(node.Target) :?> IComponent
 
-    member this.SetBody(body: ComponentBody) =
-        _body <- body
-        this.Render()
+            match currOpt with
+            | ValueNone -> failwith "Component widget must have a body"
+            | ValueSome body -> target.SetBody(body))
 
-    member this.SetContext(context: ComponentContext) =
-        _contextSubscription.Dispose()
-        _contextSubscription <- context.RenderNeeded.Subscribe(this.Render)
-        _context <- context
-        this.Render()
+    let Context =
+        Attributes.defineSimpleScalar "Component_Context" ScalarAttributeComparers.equalityCompare (fun _ currOpt node ->
+            let target = getAttachedComponent(node.Target) :?> IComponent
+
+            match currOpt with
+            | ValueNone -> target.SetContext(ComponentContext())
+            | ValueSome context -> target.SetContext(context))
+
+type Component(treeContext: ViewTreeContext, body: ComponentBody, context: ComponentContext) =
+    let mutable _body = body
+    let mutable _context = context
+    let mutable _widget = Unchecked.defaultof<_>
+    let mutable _view = null
+    let mutable _contextSubscription: IDisposable = null
+
+    interface IComponent with
+        member this.SetBody(body: ComponentBody) =
+            _body <- body
+            this.Render()
+
+        member this.SetContext(context: ComponentContext) =
+            _contextSubscription.Dispose()
+            _contextSubscription <- context.RenderNeeded.Subscribe(this.Render)
+            _context <- context
+            this.Render()
+
+        member this.Dispose() =
+            if _contextSubscription <> null then
+                _contextSubscription.Dispose()
+                _contextSubscription <- null
 
     member this.CreateView(componentWidget: Widget) =
         let struct (context, rootWidget) = _body.Invoke(_context)
@@ -246,7 +276,8 @@ type Component(treeContext: ViewTreeContext, body: ComponentBody, context: Compo
         let scalars =
             match componentWidget.ScalarAttributes with
             | ValueNone -> ValueNone
-            | ValueSome attrs -> ValueSome(Array.skip 2 attrs) // Skip the Component_Body and Component_Context attributes
+            | ValueSome attrs ->
+                ValueSome(Array.filter (fun (attr: ScalarAttribute) -> attr.Key <> Component.Body.Key && attr.Key <> Component.Context.Key) attrs)
 
         let rootWidget: Widget =
             { Key = rootWidget.Key
@@ -277,7 +308,7 @@ type Component(treeContext: ViewTreeContext, body: ComponentBody, context: Compo
         let struct (node, view) = widgetDef.CreateView(rootWidget, treeContext, ValueNone)
         _view <- view
 
-        Component.SetAttachedComponent(view, this)
+        Component.setAttachedComponent view this
 
         _contextSubscription <- _context.RenderNeeded.Subscribe(this.Render)
 
@@ -298,31 +329,7 @@ type Component(treeContext: ViewTreeContext, body: ComponentBody, context: Compo
 
         Reconciler.update treeContext.CanReuseView (ValueSome prevRootWidget) currRootWidget viewNode
 
-    interface IDisposable with
-        member this.Dispose() =
-            if _contextSubscription <> null then
-                _contextSubscription.Dispose()
-                _contextSubscription <- null
-
-module Component =
-    /// TODO: This is actually broken. On every call of the parent, the body will be reassigned to the Component triggering a re-render because of the noCompare.
-    /// This is not what was expected. The body should actually be invalidated based on its context.
-    let Body =
-        Attributes.defineSimpleScalar "Component_Body" ScalarAttributeComparers.noCompare (fun _ currOpt node ->
-            let target = Component.GetAttachedComponent(node.Target)
-
-            match currOpt with
-            | ValueNone -> failwith "Component widget must have a body"
-            | ValueSome body -> target.SetBody(body))
-
-    let Context =
-        Attributes.defineSimpleScalar "Component_Context" ScalarAttributeComparers.equalityCompare (fun _ currOpt node ->
-            let target = Component.GetAttachedComponent(node.Target)
-
-            match currOpt with
-            | ValueNone -> target.SetContext(ComponentContext())
-            | ValueSome context -> target.SetContext(context))
-
+module ComponentWidget =
     let WidgetKey =
         let key = WidgetDefinitionStore.getNextKey()
 
@@ -334,17 +341,17 @@ module Component =
               CreateView =
                 fun (widget, treeContext, _) ->
                     match widget.ScalarAttributes with
-                    | ValueNone -> failwith "Component widget must have a body"
+                    | ValueNone -> failwith "Component widget must have a body and a context"
                     | ValueSome attrs ->
                         let body =
-                            match Array.tryFind (fun (attr: ScalarAttribute) -> attr.Key = Body.Key) attrs with
+                            match Array.tryFind (fun (attr: ScalarAttribute) -> attr.Key = Component.Body.Key) attrs with
                             | Some attr -> attr.Value :?> ComponentBody
                             | None -> failwith "Component widget must have a body"
 
                         let context =
-                            match Array.tryFind (fun (attr: ScalarAttribute) -> attr.Key = Context.Key) attrs with
+                            match Array.tryFind (fun (attr: ScalarAttribute) -> attr.Key = Component.Context.Key) attrs with
                             | Some attr -> attr.Value :?> ComponentContext
-                            | None -> failwith "Component widget must have a context"
+                            | None -> ComponentContext()
 
                         let comp = new Component(treeContext, body, context)
                         let struct (node, view) = comp.CreateView(widget)

src/Fabulous/Component/Context.fs

@@ -1,5 +1,7 @@
 namespace Fabulous
 
+open System.ComponentModel
+
 (*
 ARCHITECTURE NOTES:
 
@@ -20,11 +22,14 @@ type binding
 /// <summary>
 /// Holds the values for the various states of a component.
 /// </summary>
-type ComponentContext() =
-    // We assume that most components will have few values, so initialize it with a small array
-    let mutable values = Array.zeroCreate 3
+type ComponentContext(initialSize: int) =
+    let mutable values = Array.zeroCreate initialSize
 
     let renderNeeded = Event<unit>()
+
+    // We assume that most components will have few values, so initialize it with a small array
+    new() = ComponentContext(3)
+
     member this.RenderNeeded = renderNeeded.Publish
     member this.NeedsRender() = renderNeeded.Trigger()
 
@@ -48,7 +53,8 @@ type ComponentContext() =
         else
             ValueSome(unbox<'T> value)
 
-    member internal this.SetValueInternal(key: int, value: 'T) = values[key] <- box value
+    [<EditorBrowsable(EditorBrowsableState.Never)>]
+    member this.SetValueInternal(key: int, value: 'T) = values[key] <- box value
 
     member this.SetValue(key: int, value: 'T) =
         values[key] <- box value