Add extraAttributes support

Fabulous.CodeGen/src/Fabulous.CodeGen/Generator/CodeGenerator.fs

@@ -62,12 +62,18 @@ module CodeGenerator =
         if immediateMembers.Length > 0 then
             w.printfn ""
             for m in immediateMembers do
-                w.printfn "        let attribCount = match %s with Some _ -> attribCount + 1 | None -> attribCount" m.Name
+                if m.Name = "extraAttributes" then
+                    w.printfn "        let attribCount = match %s with Some extraAttributes -> attribCount + extraAttributes.Length | None -> attribCount" m.Name
+                else
+                    w.printfn "        let attribCount = match %s with Some _ -> attribCount + 1 | None -> attribCount" m.Name
+
+            w.printfn "        let extraCount = match extraAttributes with Some extraAttributes -> extraAttributes.Length | None -> 0"
             w.printfn ""
 
+
         match data.BaseName with 
         | None ->
-            w.printfn "        let attribBuilder = AttributesBuilder(attribCount)"
+            w.printfn "        let attribBuilder = AttributesBuilder(attribCount, extraCount)"
         | Some nameOfBaseCreator ->
             let baseMemberNewLine = "\n                                              " + String.replicate nameOfBaseCreator.Length " " + " "
             let baseMembers =
@@ -284,7 +290,7 @@ module CodeGenerator =
             w.printfn ""
             w.printfn "        let attribBuilder = ViewBuilders.Build%s(0%s)" data.Name membersForBuild
             w.printfn ""
-            w.printfn "        ViewElement.Create<%s>(ViewBuilders.Create%s, (fun registry prevOpt curr target -> ViewBuilders.Update%s(registry, prevOpt, curr, target)), attribBuilder)" data.FullName data.Name data.Name
+            w.printfn "        ViewElement.Create<%s>(ViewBuilders.Create%s, (fun registry prevOpt curr target -> ViewBuilders.Update%s(registry, prevOpt, curr, target)), attribBuilder, extraAttributes)" data.FullName data.Name data.Name
             w.printfn ""
 
 

Fabulous.XamarinForms/src/Fabulous.XamarinForms/Xamarin.Forms.Core.json

@@ -32,6 +32,13 @@
           "customAttributeKey": "Fabulous.XamarinForms.ViewExtensions.TagAttribKey",
           "defaultValue": "null",
           "inputType": "obj"
+        },
+        {
+          "source": null,
+          "name": "ExtraAttributes",
+          "canBeUpdated": false,
+          "defaultValue": "null",
+          "inputType": "(ViewElement -> ViewElement) list"
         }
       ],
       "events": [

src/Fabulous/ViewElement.fs

@@ -37,10 +37,12 @@ type AttributeKey<'T> internal (keyv: int) =
 
 
 /// A description of a visual element
-type AttributesBuilder (attribCount: int) = 
+type AttributesBuilder (attribCount: int, extraCount: int) = 
+
+    let mutable count = extraCount
+    let mutable attribs = Array.zeroCreate<KeyValuePair<int, obj>>(attribCount)
 
-    let mutable count = 0
-    let mutable attribs = Array.zeroCreate<KeyValuePair<int, obj>>(attribCount)    
+    new (attribCount) = AttributesBuilder(attribCount, 0)
 
     /// Get the attributes of the visual element
     [<DebuggerBrowsable(DebuggerBrowsableState.RootHidden)>]
@@ -108,9 +110,11 @@ type ViewRef<'T when 'T : not struct>() =
 /// A description of a visual element
 type ViewElement internal (targetType: Type, create: (unit -> obj), update: (ViewElement voption -> ViewElement -> obj -> unit), attribs: KeyValuePair<int,obj>[]) = 
 
+    let extraAttribsCounter = ref 0
+
     new (targetType: Type, create: (unit -> obj), update: (ViewElement voption -> ViewElement -> obj -> unit), attribsBuilder: AttributesBuilder) =
         ViewElement(targetType, create, update, attribsBuilder.Close())
-
+    
     static member Create
             (create: (unit -> 'T),
              update: (Dictionary<int, ViewElement voption -> ViewElement -> obj -> unit> -> ViewElement voption -> ViewElement -> 'T -> unit),
@@ -122,6 +126,24 @@ type ViewElement internal (targetType: Type, create: (unit -> obj), update: (Vie
             attribsBuilder.Close()
         )
 
+    static member Create
+            (create: (unit -> 'T),
+             update: (Dictionary<int, ViewElement voption -> ViewElement -> obj -> unit> -> ViewElement voption -> ViewElement -> 'T -> unit),
+             attribsBuilder: AttributesBuilder,
+             extraAttributes: (ViewElement -> ViewElement) list option) =
+        let viewElement =
+            ViewElement(
+                typeof<'T>, (create >> box),
+                (fun prev curr target -> update (Dictionary()) prev curr (unbox target)),
+                attribsBuilder.Close()
+            )
+
+        match extraAttributes with
+        | Some extraAttributes when extraAttributes.Length > 0 ->
+            viewElement.WithExtraAttributes(extraAttributes)
+        | _ ->
+            viewElement
+
     static member val CreatedAttribKey : AttributeKey<obj -> unit> = AttributeKey<_>("Created")
     static member val RefAttribKey : AttributeKey<ViewRef> = AttributeKey<_>("Ref")
     static member val KeyAttribKey : AttributeKey<string> = AttributeKey<_>("Key")
@@ -180,7 +202,7 @@ type ViewElement internal (targetType: Type, create: (unit -> obj), update: (Vie
         target
 
     /// Produce a new visual element with an adjusted attribute
-    member __.WithAttribute(key: AttributeKey<'T>, value: 'T) =
+    member x.WithAttribute(key: AttributeKey<'T>, value: 'T) =
         let duplicateViewElement newAttribsLength attribIndex =
             let attribs2 = Array.zeroCreate newAttribsLength
             Array.blit attribs 0 attribs2 0 attribs.Length
@@ -194,8 +216,18 @@ type ViewElement internal (targetType: Type, create: (unit -> obj), update: (Vie
         | Some i ->
             duplicateViewElement n i // duplicate and replace existing attribute
         | None ->
-            duplicateViewElement (n + 1) n // duplicate and add new attribute
-
+            if attribs.[!extraAttribsCounter] = Unchecked.defaultof<KeyValuePair<_,_>> then
+              attribs.[!extraAttribsCounter] <- KeyValuePair(key.KeyValue, box value)
+              incr extraAttribsCounter
+              x
+            else          
+              duplicateViewElement (n + 1) n // duplicate and add new attribute
+
+    member x.WithExtraAttributes(extraAttributes: (ViewElement -> ViewElement) list) =
+        if extraAttributes.Length > 0
+        then extraAttributes |> Seq.map (fun apply -> apply x) |> Seq.last
+        else x
+
     override x.ToString() = sprintf "%s(...)@%d" x.TargetType.Name (x.GetHashCode())