Apply modifiers as they change in ViewFlexContainer (#2357)

* Apply modifiers as they change in ViewFlexContainer

This reduces the amount of preparation required to measure a layout.

* Spotless

* apiDump

redwood-layout-view/src/main/kotlin/app/cash/redwood/layout/view/ViewFlexContainer.kt

@@ -45,12 +45,7 @@ internal class ViewFlexContainer(
   private val direction: FlexDirection,
 ) : YogaFlexContainer<View>,
   ChangeListener {
-  private val yogaLayout: YogaLayout = YogaLayout(
-    context,
-    applyModifier = { node, index ->
-      node.applyModifier(children.widgets[index].modifier, density)
-    },
-  )
+  private val yogaLayout: YogaLayout = YogaLayout(context)
   override val rootNode: Node get() = yogaLayout.rootNode
   override val density = Density(context.resources)
 
@@ -59,14 +54,26 @@ internal class ViewFlexContainer(
 
   override val children = ViewGroupChildren(
     yogaLayout,
-    insert = { index, view ->
-      yogaLayout.rootNode.children.add(index, view.asNode())
+    insert = { index, widget ->
+      val view = widget.value
+
+      val node = view.asNode()
+      yogaLayout.rootNode.children.add(index, node)
+
+      // Always apply changes *after* adding a node to its parent.
+      node.applyModifier(widget.modifier, density)
+
       yogaLayout.addView(view, index)
     },
     remove = { index, count ->
       yogaLayout.rootNode.children.remove(index, count)
       yogaLayout.removeViews(index, count)
     },
+    onModifierUpdated = { index, widget ->
+      val node = yogaLayout.rootNode.children[index]
+      node.applyModifier(widget.modifier, density)
+      yogaLayout.requestLayout()
+    },
   )
 
   private var onScroll: ((Px) -> Unit)? = null

redwood-layout-view/src/main/kotlin/app/cash/redwood/layout/view/YogaLayout.kt

@@ -15,10 +15,7 @@ import app.cash.redwood.yoga.Size
 import kotlin.math.roundToInt
 
 @SuppressLint("ViewConstructor")
-internal class YogaLayout(
-  context: Context,
-  private val applyModifier: (Node, Int) -> Unit,
-) : ViewGroup(context) {
+internal class YogaLayout(context: Context) : ViewGroup(context) {
   val rootNode = Node()
 
   private fun applyLayout(node: Node, xOffset: Float, yOffset: Float) {
@@ -85,11 +82,6 @@ internal class YogaLayout(
       MeasureSpec.UNSPECIFIED -> {}
     }
 
-    // This must be applied immediately before measure.
-    for ((index, node) in rootNode.children.withIndex()) {
-      applyModifier(node, index)
-    }
-
     // Sync widget layout requests to the Yoga node tree.
     for (node in rootNode.children) {
       if (node.view?.isLayoutRequested == true) {

redwood-widget/api/android/redwood-widget.api

@@ -75,8 +75,8 @@ public abstract interface class app/cash/redwood/widget/SavedStateRegistry {
 }
 
 public final class app/cash/redwood/widget/ViewGroupChildren : app/cash/redwood/widget/Widget$Children {
-	public fun <init> (Landroid/view/ViewGroup;Lkotlin/jvm/functions/Function2;Lkotlin/jvm/functions/Function2;)V
-	public synthetic fun <init> (Landroid/view/ViewGroup;Lkotlin/jvm/functions/Function2;Lkotlin/jvm/functions/Function2;ILkotlin/jvm/internal/DefaultConstructorMarker;)V
+	public fun <init> (Landroid/view/ViewGroup;Lkotlin/jvm/functions/Function2;Lkotlin/jvm/functions/Function2;Lkotlin/jvm/functions/Function2;)V
+	public synthetic fun <init> (Landroid/view/ViewGroup;Lkotlin/jvm/functions/Function2;Lkotlin/jvm/functions/Function2;Lkotlin/jvm/functions/Function2;ILkotlin/jvm/internal/DefaultConstructorMarker;)V
 	public fun detach ()V
 	public fun getWidgets ()Ljava/util/List;
 	public fun insert (ILapp/cash/redwood/widget/Widget;)V

redwood-widget/src/androidMain/kotlin/app/cash/redwood/widget/ViewGroupChildren.kt

@@ -20,36 +20,36 @@ import android.view.ViewGroup
 
 public class ViewGroupChildren(
   private val container: ViewGroup,
-  private val insert: (index: Int, view: View) -> Unit = { index, view ->
-    container.addView(view, index)
+  private val insert: (index: Int, widget: Widget<View>) -> Unit = { index, widget ->
+    container.addView(widget.value, index)
   },
   private val remove: (index: Int, count: Int) -> Unit = { index, count ->
     container.removeViews(index, count)
   },
+  private val onModifierUpdated: (index: Int, widget: Widget<View>) -> Unit = { _, _ ->
+    container.requestLayout()
+  },
 ) : Widget.Children<View> {
   private val _widgets = ArrayList<Widget<View>>()
   override val widgets: List<Widget<View>> get() = _widgets
 
   override fun insert(index: Int, widget: Widget<View>) {
     _widgets.add(index, widget)
-    insert(index, widget.value)
+    insert.invoke(index, widget)
   }
 
   override fun move(fromIndex: Int, toIndex: Int, count: Int) {
     _widgets.move(fromIndex, toIndex, count)
 
-    val views = Array(count) { offset ->
-      container.getChildAt(fromIndex + offset)
-    }
     remove.invoke(fromIndex, count)
 
     val newIndex = if (toIndex > fromIndex) {
       toIndex - count
     } else {
       toIndex
     }
-    views.forEachIndexed { offset, view ->
-      insert(newIndex + offset, view)
+    for (i in newIndex until newIndex + count) {
+      insert.invoke(i, _widgets[i])
     }
   }
 
@@ -59,7 +59,7 @@ public class ViewGroupChildren(
   }
 
   override fun onModifierUpdated(index: Int, widget: Widget<View>) {
-    container.requestLayout()
+    onModifierUpdated.invoke(index, widget)
   }
 
   override fun detach() {