Allows controls to pass state to descendants (similar to swift UI env…

…ironment objects & react contexts) (#278)

src/Avalonia.FuncUI.sln

@@ -67,6 +67,8 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Examples.Mobile", "Examples
 EndProject
 Project("{F2A71F9B-5D33-465A-A702-920D77279786}") = "Examples.Mobile.iOS", "Examples\Examples.Mobile.iOS\Examples.Mobile.iOS.fsproj", "{44E60326-957D-4022-8E67-669161AFF957}"
 EndProject
+Project("{F2A71F9B-5D33-465A-A702-920D77279786}") = "Examples.EnvApp", "Examples\Component Examples\Examples.EnvApp\Examples.EnvApp.fsproj", "{90E18FDC-8B2A-4C21-B60D-B5B7A14648A3}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -161,6 +163,10 @@ Global
 		{44E60326-957D-4022-8E67-669161AFF957}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{44E60326-957D-4022-8E67-669161AFF957}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{44E60326-957D-4022-8E67-669161AFF957}.Release|Any CPU.Build.0 = Release|Any CPU
+		{90E18FDC-8B2A-4C21-B60D-B5B7A14648A3}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{90E18FDC-8B2A-4C21-B60D-B5B7A14648A3}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{90E18FDC-8B2A-4C21-B60D-B5B7A14648A3}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{90E18FDC-8B2A-4C21-B60D-B5B7A14648A3}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -188,6 +194,7 @@ Global
 		{01631D41-54F9-4815-8B26-9F1BEEC22F7A} = {5DB968C6-935E-41AC-A252-644B4886AF8A}
 		{AD6796F9-45CA-4FBA-9673-E6FC9214C80D} = {84811DB3-C276-4F0D-B3BA-78B88E2C6EF0}
 		{44E60326-957D-4022-8E67-669161AFF957} = {AD6796F9-45CA-4FBA-9673-E6FC9214C80D}
+		{90E18FDC-8B2A-4C21-B60D-B5B7A14648A3} = {F50826CE-D9BC-45CF-A110-C42225B75AD3}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {4630E817-6780-4C98-9379-EA3B45224339}

src/Avalonia.FuncUI/Avalonia.FuncUI.fsproj

@@ -146,6 +146,7 @@
     <Compile Include="DSL\TickBar.fs" />
     <Compile Include="DSL\Viewbox.fs" />
     <Compile Include="DSL\SelectableTextBlock.fs" />
+    <Compile Include="Environment.fs" />
   </ItemGroup>
 
   <ItemGroup>

src/Avalonia.FuncUI/Components/Context/Context.fs

@@ -57,7 +57,7 @@ type IComponentContext =
     /// <example>
     /// <code>
     /// Component (fun ctx ->
-    ///     (* expensive operation that should only happen once on initialisation *) 
+    ///     (* expensive operation that should only happen once on initialisation *)
     ///     let count = ctx.useStateLazy (fun () -> Math.Sqrt(42))
     ///     ..
     ///     // id will have the same value during the whole component lifetime. (unless changed via 'id.Set ..')
@@ -88,6 +88,23 @@ type IComponentContext =
     /// <param name="renderOnChange">re-render component on change (default: true).</param>
     abstract usePassed<'value> : value: IWritable<'value> * ?renderOnChange: bool -> IWritable<'value>
 
+    /// <summary>
+    /// Attaches a passed <c>IWritable&lt;'value&gt;</c> value to the component context.
+    /// <example>
+    /// <code>
+    /// let countView (count: IWritable&lt;int&gt;) =
+    ///     Component (fun ctx ->
+    ///         // attach passed writable value to the component context
+    ///         let count = ctx.usePassedLazy (fun _ -> (* expensive function that returns IWritable*))
+    ///         ..
+    ///     )
+    /// </code>
+    /// </example>
+    /// </summary>
+    /// <param name="obtainValue">(expensive) function that returns an IWritable.</param>
+    /// <param name="renderOnChange">re-render component on change (default: true).</param>
+    abstract usePassedLazy<'value> : obtainValue: (unit -> IWritable<'value>) * ?renderOnChange: bool -> IWritable<'value>
+
     /// <summary>
     /// Attaches a passed <c>IReadable&lt;'value&gt;</c> value to the component context.
     /// <example>
@@ -318,6 +335,15 @@ type Context (componentControl: Avalonia.Controls.Border) =
                 )
             ) :?> IWritable<'value>
 
+        member this.usePassedLazy (obtainState: unit -> IWritable<'value>, ?renderOnChange: bool) =
+            this.useStateHook<'value>(
+                StateHook.Create (
+                    identity = callingIndex,
+                    state = StateHookValue.Lazy (fun _ -> obtainState() :> IAnyReadable),
+                    renderOnChange = defaultArg renderOnChange true
+                )
+            ) :?> IWritable<'value>
+
         member this.usePassedRead(value: IReadable<'t>, ?renderOnChange: bool) =
             this.useStateHook<'value>(
                 StateHook.Create (
@@ -345,7 +371,6 @@ type Context (componentControl: Avalonia.Controls.Border) =
                 )
             ) :?> IWritable<'value>
 
-
         member this.control = componentControl
 
     interface IDisposable with

src/Avalonia.FuncUI/Environment.fs

@@ -0,0 +1,91 @@
+namespace Avalonia.FuncUI
+
+open System
+open Avalonia.Controls
+open Avalonia.FuncUI.Types
+open Avalonia.FuncUI.DSL
+open Avalonia.LogicalTree
+open Avalonia.Styling
+#nowarn "57"
+
+type EnvironmentState<'value> =
+    internal {
+        Name: string
+        DefaultValue: IWritable<'value> option
+    }
+
+    [<Experimental "this feature is experimental. The API might change.">]
+    static member Create (name: string, ?defaultValue: IWritable<'value>) : EnvironmentState<'value> =
+        { Name = name
+          DefaultValue = defaultValue }
+
+[<Experimental "this feature is experimental. The API might change.">]
+[<AllowNullLiteral>]
+type EnvironmentStateProvider<'value>
+  ( state: EnvironmentState<'value>,
+    providedState: IWritable<'value>) as this =
+
+    inherit ContentControl ()
+
+    member this.EnvironmentState with get () = state
+
+    member this.ProvidedState with get () = providedState
+
+    interface IStyleable with
+        member this.StyleKey = typeof<ContentControl>
+
+type EnvironmentStateProvider<'value> with
+
+    [<Experimental "this feature is experimental. The API might change.">]
+    static member create (state: EnvironmentState<'value>, providedValue: IWritable<'value>, content: IView) =
+        { View.ViewType = typeof<EnvironmentStateProvider<'value>>
+          View.ViewKey = ValueNone
+          View.Attrs = [ ContentControl.content content ]
+          View.Outlet = ValueNone
+          View.ConstructorArgs = [| state :> obj; providedValue :> obj |] }
+        :> IView<EnvironmentStateProvider<'value>>
+
+type EnvironmentState<'value> with
+
+    [<Experimental "this feature is experimental. The API might change.">]
+    member this.provide (providedValue: IWritable<'value>, content: IView) =
+        EnvironmentStateProvider<'value>.create(this, providedValue, content)
+
+[<RequireQualifiedAccess>]
+module private EnvironmentStateConsumer =
+
+    let rec private tryFindNext (control: EnvironmentStateProvider<'value>, state: EnvironmentState<'value>) =
+        match control.FindLogicalAncestorOfType<EnvironmentStateProvider<'value>>(includeSelf = false) with
+        | null -> ValueNone
+        | ancestor ->
+            if ancestor.EnvironmentState.Name.Equals(state.Name, StringComparison.Ordinal) then
+                ValueSome ancestor.ProvidedState
+            else
+                tryFindNext (ancestor, state)
+
+    let tryFind (control: Control, state: EnvironmentState<'value>) =
+        match control.FindLogicalAncestorOfType<EnvironmentStateProvider<'value>>(includeSelf = false) with
+        | null -> ValueNone
+        | ancestor ->
+            if ancestor.EnvironmentState.Name.Equals(state.Name, StringComparison.Ordinal) then
+                ValueSome ancestor.ProvidedState
+            else
+                tryFindNext (ancestor, state)
+
+[<AutoOpen>]
+module __ContextExtensions_useEnvHook =
+
+    type IComponentContext with
+
+        [<Experimental "this feature is experimental. The API might change.">]
+        member this.useEnvState (state: EnvironmentState<'value>, ?renderOnChange: bool) =
+           let obtainValue () =
+               match EnvironmentStateConsumer.tryFind (this.control, state), state.DefaultValue with
+               | ValueSome value, _ -> value
+               | ValueNone, Some defaultValue -> defaultValue
+               | ValueNone, None -> failwithf "No value provided for environment state '%s'" state.Name
+
+           this.usePassedLazy (
+               obtainValue = obtainValue,
+               ?renderOnChange = renderOnChange
+           )

src/Directory.Build.props

@@ -1,6 +1,6 @@
 <Project>
   <PropertyGroup>
     <AvaloniaVersion>11.0.0-preview5</AvaloniaVersion>
-    <FuncUIVersion>0.6.0-preview8</FuncUIVersion>
+    <FuncUIVersion>0.6.0-preview9</FuncUIVersion>
   </PropertyGroup>
 </Project>

src/Examples/Component Examples/Examples.EnvApp/Examples.EnvApp.fsproj

@@ -0,0 +1,19 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <OutputType>Exe</OutputType>
+        <TargetFramework>net6.0</TargetFramework>
+    </PropertyGroup>
+
+    <ItemGroup>
+        <Compile Include="Program.fs"/>
+    </ItemGroup>
+
+    <ItemGroup>
+        <PackageReference Include="Avalonia.Desktop" Version="$(AvaloniaVersion)" />
+        <PackageReference Include="Avalonia.Themes.Fluent" Version="$(AvaloniaVersion)" />
+        <ProjectReference Include="..\..\..\Avalonia.FuncUI.Elmish\Avalonia.FuncUI.Elmish.fsproj" />
+        <ProjectReference Include="..\..\..\Avalonia.FuncUI\Avalonia.FuncUI.fsproj" />
+    </ItemGroup>
+
+</Project>