Render Picker as a spinner

Demo/App.swiftpm/Sources/ControlsScreen.swift

@@ -19,6 +19,9 @@ struct ControlsScreen: View {
     @State
     private var name = ""
 
+    @State
+    private var fruit = "Apple"
+
     var body: some View {
         ScrollView {
             VStack(spacing: 24) {
@@ -43,6 +46,14 @@ struct ControlsScreen: View {
                 Text("Text field")
                 TextField("Name", text: $name)
                 Text(name.isEmpty ? "Nothing typed yet" : "Hello, \(name)")
+                Divider()
+                Text("Picker")
+                Picker("Fruit", selection: $fruit) {
+                    Text("Apple").tag("Apple")
+                    Text("Banana").tag("Banana")
+                    Text("Cherry").tag("Cherry")
+                }
+                Text("Selected: \(fruit)")
             }
         }
     }

Demo/app/src/main/java/com/pureswift/swiftandroid/SpinnerOnItemSelectedListener.kt

@@ -0,0 +1,21 @@
+package com.pureswift.swiftandroid
+
+import android.view.View
+import android.widget.AdapterView
+import android.widget.Spinner
+
+class SpinnerOnItemSelectedListener(val action: SwiftObject): AdapterView.OnItemSelectedListener {
+
+    /// Registers itself on the spinner, so Swift does not need a binding for the listener type.
+    fun attach(spinner: Spinner) {
+        spinner.setOnItemSelectedListener(this)
+    }
+
+    override fun onItemSelected(parent: AdapterView<*>?, view: View?, position: Int, id: Long) {
+        onItemSelectedSwift(position)
+    }
+
+    override fun onNothingSelected(parent: AdapterView<*>?) { }
+
+    external fun onItemSelectedSwift(position: Int)
+}

Sources/AndroidSwiftUI/AndroidPicker.swift

@@ -0,0 +1,144 @@
+//
+//  AndroidPicker.swift
+//  AndroidSwiftUI
+//
+//  Created by Alsey Coleman Miller on 7/22/26.
+//
+
+import AndroidKit
+
+extension _PickerContainer: AndroidPrimitive {
+
+    var renderedBody: AnyView {
+        let options = Self.options(of: self)
+        return AnyView(AndroidSpinner(
+            selection: $selection,
+            titles: options.map(\.title),
+            values: options.map(\.value)
+        ))
+    }
+}
+
+private extension _PickerContainer {
+
+    struct Option {
+
+        let title: String
+
+        let value: SelectionValue
+    }
+
+    /// The pickable options, in order.
+    ///
+    /// `elements` covers the `ForEach`-with-data case, where the identity is the selection
+    /// value. Otherwise the container's content — the generated `ForEach` of
+    /// `_PickerElement`s that `Picker.body` builds, each wrapped in conditional content —
+    /// is flattened, and each element's row is walked for the `tag(_:)` that associates it
+    /// with its value.
+    static func options(of container: Self) -> [Option] {
+        if !container.elements.isEmpty {
+            return container.elements.compactMap { element in
+                guard let value = element.anyId.base as? SelectionValue else { return nil }
+                return Option(title: title(of: element.anyContent), value: value)
+            }
+        }
+        return pickerElements(in: AnyView(container.content)).compactMap { element in
+            guard let value = tag(of: element.content.view) else { return nil }
+            return Option(title: title(of: element.content), value: value)
+        }
+    }
+
+    /// Recursively flattens group views to the `_PickerElement` rows they contain.
+    /// `ForEach` wraps each row in an identified view, which is descended through its
+    /// content.
+    static func pickerElements(in view: AnyView) -> [_PickerElement] {
+        if let element = mapAnyView(view, transform: { (element: _PickerElement) in element }) {
+            return [element]
+        }
+        if let identified = view.view as? _AnyIDView {
+            return pickerElements(in: identified.anyContent)
+        }
+        guard let group = view.view as? GroupView else { return [] }
+        return group.children.flatMap { pickerElements(in: $0) }
+    }
+
+    /// The value written by `tag(_:)`, if any.
+    static func tag(of view: Any) -> SelectionValue? {
+        var view = view
+        while let modified = view as? _AnyModifiedContent {
+            if let modifier = modified.anyModifier as? _TraitWritingModifier<TagValueTraitKey<SelectionValue>>,
+               case let .tagged(value) = modifier.value {
+                return value
+            }
+            view = modified.anyContent
+        }
+        return nil
+    }
+
+    /// The text a row displays, unwrapping any modifiers (such as the tag itself) around
+    /// it. Rows that aren't text render as an empty entry, since a spinner shows plain
+    /// strings rather than arbitrary views.
+    static func title(of view: AnyView) -> String {
+        var view = view.view
+        while let modified = view as? _AnyModifiedContent {
+            view = modified.anyContent
+        }
+        return (view as? Text).map { _TextProxy($0).rawText } ?? ""
+    }
+}
+
+/// Native spinner bound to the selected value.
+struct AndroidSpinner<SelectionValue: Hashable> {
+
+    @Binding
+    var selection: SelectionValue
+
+    let titles: [String]
+
+    let values: [SelectionValue]
+}
+
+extension AndroidSpinner: AndroidViewRepresentable {
+
+    typealias Coordinator = Void
+
+    func makeAndroidView(context: Self.Context) -> AndroidWidget.Spinner {
+        let view = AndroidWidget.Spinner(context.androidContext)
+        // a spinner that hugs its content collapses to the dropdown arrow, hiding the
+        // selected value; span the stack like the other horizontal controls
+        view.setLayoutParams(ViewGroup.LayoutParams(
+            try! JavaClass<ViewGroup.LayoutParams>().MATCH_PARENT,
+            try! JavaClass<ViewGroup.LayoutParams>().WRAP_CONTENT
+        ))
+        applyAdapter(to: view, context: context.androidContext)
+        // attached after the adapter so the initial selection doesn't call back
+        let listener = SpinnerOnItemSelectedListener { position in
+            guard let value = self.values.indices.contains(Int(position)) ? self.values[Int(position)] : nil,
+                  value != self.selection else { return }
+            self.selection = value
+        }
+        listener.attach(view)
+        return view
+    }
+
+    func updateAndroidView(_ view: AndroidWidget.Spinner, context: Self.Context) {
+        applyAdapter(to: view, context: view.getContext())
+    }
+}
+
+private extension AndroidSpinner {
+
+    func applyAdapter(to view: AndroidWidget.Spinner, context: AndroidContent.Context?) {
+        guard let context else { return }
+        let layout = try! JavaClass<AndroidR.R.layout>().simple_spinner_dropdown_item
+        let adapter = AndroidWidget.ArrayAdapter<JavaObject>(
+            context: context,
+            resource: layout,
+            objects: titles.map { JavaString($0).as(JavaObject.self) }
+        )
+        view.setAdapter(adapter.as(AndroidWidget.SpinnerAdapter.self))
+        if let index = values.firstIndex(of: selection), view.getSelectedItemPosition() != Int32(index) {
+            view.setSelection(Int32(index))
+        }
+    }
+}

Sources/AndroidSwiftUI/OnItemSelectedListener.swift

@@ -0,0 +1,54 @@
+//
+//  OnItemSelectedListener.swift
+//  AndroidSwiftUI
+//
+//  Created by Alsey Coleman Miller on 7/22/26.
+//
+
+import Foundation
+import AndroidKit
+
+/// Bridges `AdapterView.OnItemSelectedListener` to Swift.
+///
+/// As with the other listener bridges, the Kotlin side forwards only the position: the
+/// native symbol is derived from this declaration, so passing the adapter view and item id
+/// through would shift the arguments.
+@JavaClass("com.pureswift.swiftandroid.SpinnerOnItemSelectedListener")
+open class SpinnerOnItemSelectedListener: JavaObject {
+
+    public typealias Action = (Int32) -> ()
+
+    @JavaMethod
+    @_nonoverride public convenience init(action: SwiftObject?, environment: JNIEnvironment? = nil)
+
+    @JavaMethod
+    public func getAction() -> SwiftObject?
+
+    /// Registers this listener on the spinner, since the listener type itself has no binding.
+    @JavaMethod
+    public func attach(_ spinner: AndroidWidget.Spinner?)
+}
+
+@JavaImplementation("com.pureswift.swiftandroid.SpinnerOnItemSelectedListener")
+extension SpinnerOnItemSelectedListener {
+
+    @JavaMethod
+    func onItemSelectedSwift(_ position: Int32) {
+        // drain queue, matching `ViewOnClickListener`
+        RunLoop.main.run(until: Date() + 0.01)
+        action(position)
+        RunLoop.main.run(until: Date() + 0.01)
+    }
+}
+
+public extension SpinnerOnItemSelectedListener {
+
+    convenience init(action: @escaping (Int32) -> (), environment: JNIEnvironment? = nil) {
+        let object = SwiftObject(action, environment: environment)
+        self.init(action: object, environment: environment)
+    }
+
+    var action: ((Int32) -> ()) {
+        getAction()!.valueObject().value as! Action
+    }
+}