Merge pull request #8 from PureSwift/feature/layout-fixes

Fix stack alignment and Spacer expansion

Author: colemancda

Sources/AndroidSwiftUI/AndroidRenderer.swift

@@ -73,6 +73,7 @@ final class AndroidRenderer: Renderer {
                     return nil
                 }
                 let viewObject = anyView.createAndroidView(context)
+                applyStackLayoutParams(for: host.view, to: viewObject, in: parentView)
                 // TODO: Determine order
                 viewGroup.addView(viewObject)
                 if let transitioning = mapAnyView(host.view, transform: { (view: AndroidTransitioningView) in view }) {
@@ -233,6 +234,28 @@ final class AndroidRenderer: Renderer {
 
 private extension AndroidRenderer {
 
+    /// Assigns layout parameters to a child added to a stack's `LinearLayout`.
+    ///
+    /// Children without their own parameters hug their content, so the stack's alignment
+    /// gravity can position them — Android's default of stretching children to match the
+    /// parent's width would leave gravity with no room to act. Views conforming to
+    /// `AndroidExpandingView` (such as `Spacer`) instead receive weighted parameters and
+    /// grow to fill the remaining space along the stack's axis.
+    func applyStackLayoutParams(for view: AnyView, to viewObject: AndroidView.View, in parentView: AndroidView.View) {
+        guard let linearLayout = parentView.as(AndroidWidget.LinearLayout.self) else { return }
+        let wrapContent = try! JavaClass<ViewGroup.LayoutParams>().WRAP_CONTENT
+        let isVertical = linearLayout.orientation == .vertical
+        if mapAnyView(view, transform: { (view: AndroidExpandingView) in view }) != nil {
+            let params = isVertical
+                ? AndroidWidget.LinearLayout.LayoutParams(wrapContent, 0, Float(1))
+                : AndroidWidget.LinearLayout.LayoutParams(0, wrapContent, Float(1))
+            viewObject.setLayoutParams(params.as(ViewGroup.LayoutParams.self))
+        } else if viewObject.getLayoutParams() == nil {
+            let params = AndroidWidget.LinearLayout.LayoutParams(wrapContent, wrapContent)
+            viewObject.setLayoutParams(params.as(ViewGroup.LayoutParams.self))
+        }
+    }
+
     /// Handler bound to the Android main looper, used to schedule reconciler updates.
     static let mainHandler = AndroidOS.Handler(try! JavaClass<AndroidOS.Looper>().getMainLooper())
 

Sources/AndroidSwiftUI/AndroidSpacer.swift

@@ -7,16 +7,21 @@
 
 import AndroidKit
 
-extension Spacer: AnyAndroidView {
+/// An Android view that expands to fill the remaining space along its parent stack's axis.
+///
+/// The renderer assigns weighted layout parameters when a conforming view is added to a
+/// `LinearLayout`, so the view grows to absorb the leftover space.
+protocol AndroidExpandingView { }
+
+extension Spacer: AnyAndroidView, AndroidExpandingView {
 
-    // NOTE: does not yet flex-grow to fill remaining space in its parent stack (that would require
-    // AndroidRenderer's generic `addView` mounting to apply per-child LayoutParams, e.g. `layout_weight`,
-    // which it doesn't do today). Rendered as a minimal-size placeholder so layouts that include a
-    // `Spacer()` (e.g. List's internal row padding) still mount without crashing.
     public func createAndroidView(_ context: AndroidContent.Context) -> AndroidView.View {
         let view = AndroidView.View(context)
+        // the renderer applies weighted layout parameters inside stacks; the minimum
+        // dimensions preserve `minLength` in either axis
         let length = Int32(minLength ?? 0)
-        view.setLayoutParams(ViewGroup.LayoutParams(length, length))
+        view.setMinimumWidth(length)
+        view.setMinimumHeight(length)
         return view
     }