Add Showcase App

.github/workflows/ci.yml

@@ -262,6 +262,9 @@ jobs:
       - name: Build swift-java-weather-app APK
         run: ./gradlew :swift-java-weather-app-weather-app:assemble${{ matrix.configuration }} --stacktrace
 
+      - name: Build swift-java-ui-showcase APK
+        run: ./gradlew :swift-java-ui-showcase-showcase-app:assemble${{ matrix.configuration }} --stacktrace
+
       - name: Build hello-cpp-swift cpp-lib
         working-directory: hello-cpp-swift/cpp-lib
         run: ./build-android-static.sh

README.md

@@ -34,6 +34,14 @@ The **[swift-java-weather-app](swift-java-weather-app/)** example showcases auto
 Swift language features, such as `async` functions and implementing a Swift `protocol` in Java,
 which can be passed ~~back~~ to Swift.
 
+The **[swift-java-ui-showcase](swift-java-ui-showcase/)** example is a "kitchen sink"
+catalog of UI components (buttons, selection controls, sliders, text inputs, and a
+validated form) where Swift owns the whole UI model: each screen's component tree,
+state, event handling, and validation are declared in Swift, and a small generic
+Kotlin/Compose renderer draws whatever Swift describes over a single JSON/JNI
+boundary. See [swift-java-ui-showcase/README.md](swift-java-ui-showcase/README.md)
+for the architecture and for how to add your own screen without touching Kotlin.
+
 ## C++ Integration Example
 
 The **[hello-cpp-swift](hello-cpp-swift/)** example demonstrates how to integrate

gradle/libs.versions.toml

@@ -11,6 +11,7 @@ constraintlayout = "2.2.1"
 lifecycleRuntimeKtx = "2.9.2"
 activityCompose = "1.10.1"
 composeBom = "2024.09.00"
+navigationCompose = "2.8.9"
 
 [libraries]
 androidx-core-ktx = { group = "androidx.core", name = "core-ktx", version.ref = "coreKtx" }
@@ -30,6 +31,7 @@ androidx-ui-test-manifest = { group = "androidx.compose.ui", name = "ui-test-man
 androidx-ui-test-junit4 = { group = "androidx.compose.ui", name = "ui-test-junit4" }
 androidx-activity-compose = { group = "androidx.activity", name = "activity-compose", version.ref = "activityCompose" }
 androidx-lifecycle-runtime-ktx = { group = "androidx.lifecycle", name = "lifecycle-runtime-ktx", version.ref = "lifecycleRuntimeKtx" }
+androidx-navigation-compose = { group = "androidx.navigation", name = "navigation-compose", version.ref = "navigationCompose" }
 
 [plugins]
 android-application = { id = "com.android.application", version.ref = "agp" }

settings.gradle.kts

@@ -48,6 +48,11 @@ project(":swift-java-weather-app-weather-lib").projectDir = file("swift-java-wea
 include(":swift-java-weather-app-weather-app")
 project(":swift-java-weather-app-weather-app").projectDir = file("swift-java-weather-app/weather-app")
 
+include(":swift-java-ui-showcase-showcase-lib")
+project(":swift-java-ui-showcase-showcase-lib").projectDir = file("swift-java-ui-showcase/showcase-lib")
+include(":swift-java-ui-showcase-showcase-app")
+project(":swift-java-ui-showcase-showcase-app").projectDir = file("swift-java-ui-showcase/showcase-app")
+
 // raw-jni examples
 include(":hello-swift-raw-jni")
 include(":hello-swift-raw-jni-callback")

swift-java-ui-showcase/.gitignore

@@ -0,0 +1,41 @@
+.DS_STORE
+
+# Swift
+.build/
+.swiftpm/
+Package.resolved
+
+# Gradle files
+.gradle/
+build/
+
+# Local configuration file (sdk path, etc)
+local.properties
+
+# Log/OS Files
+*.log
+
+# Android Studio generated files and folders
+captures/
+.externalNativeBuild/
+.cxx/
+*.aab
+*.apk
+output-metadata.json
+
+# IntelliJ
+*.iml
+.idea/
+misc.xml
+deploymentTargetDropDown.xml
+render.experimental.xml
+
+# Keystore files
+*.jks
+*.keystore
+
+# Google Services (e.g. APIs or Firebase)
+google-services.json
+
+# Android Profiling
+*.hprof

swift-java-ui-showcase/README.md

@@ -0,0 +1,156 @@
+# Swift-driven UI showcase
+
+A "kitchen sink" catalog app where **Swift declares the UI and owns all of its
+state**, and Kotlin is only a thin generic renderer. Browse screens that demo
+buttons, selection controls (switch, checkboxes, radio group), sliders, text
+inputs, and a form with validation — every component you see was declared by
+Swift code, and every interaction is handled by Swift code.
+
+| Home (Swift's screen registry) | Buttons (Swift tap counter) | Form (Swift validation) |
+|---|---|---|
+| ![Home screen](resources/home.png) | ![Buttons screen](resources/buttons.png) | ![Form validation errors](resources/form-validation.png) |
+
+## Overview
+
+The example consists of two components:
+
+- **showcase-lib**: A Swift package (`ShowcaseKit`) that declares the component
+  tree of every screen, holds all UI state, reduces every action, and validates
+  the form. It is exposed to Java by
+  [swift-java](https://github.com/swiftlang/swift-java)'s JExtract in JNI mode.
+- **showcase-app**: A Kotlin Android app whose Compose code never hard-codes a
+  screen. It interprets whatever component tree Swift returns
+  (`ComponentRenderer.kt` is a single `when` over the component kind) and
+  builds its navigation graph from Swift's screen registry.
+
+Jetpack Compose cannot be called from Swift (composables are a Kotlin compiler
+feature), so "the UI is written in Swift" takes this shape: a unidirectional
+data-flow loop with Swift as the single source of truth.
+
+```
+        Compose (Kotlin)                              ShowcaseKit (Swift)
+  ┌──────────────────────────┐                 ┌────────────────────────────┐
+  │ user taps / types / drags │──── action ───▶│ showcaseDispatch(screen,   │
+  │                          │    (JSON)       │   component, action)       │
+  │ render component tree    │                 │   → screen reduces action, │
+  │ (one `when` over "kind") │◀─ new screen ───│     mutates its Swift state│
+  └──────────────────────────┘    (JSON)       └────────────────────────────┘
+```
+
+Only three functions cross the boundary, all `(String...) -> String`
+(see `showcase-lib/Sources/ShowcaseKit/ShowcaseAPI.swift`):
+
+| Function | Purpose |
+|---|---|
+| `showcaseScreens()` | Screen registry (ids + titles) — drives the navigation graph |
+| `showcaseScreen(id)` | Current component tree of one screen |
+| `showcaseDispatch(screenId, componentId, actionJSON)` | Apply a user action, return the new tree |
+
+Because state lives in Swift, it survives navigation: toggle a switch, leave
+the screen, come back — the switch is still on, with no ViewModel or saved
+state on the Kotlin side.
+
+## Prerequisites
+
+Same as [hello-swift-java](../hello-swift-java/README.md): a Swift 6.3+
+toolchain via `swiftly`, the Swift SDK for Android, and the `swiftkit-core`
+package published to your local Maven repository. Follow the
+[Setup and Configuration](../hello-swift-java/README.md#setup-and-configuration)
+steps there (run the `swift package resolve` / `publishToMavenLocal` step from
+`swift-java-ui-showcase/showcase-lib` or any other swift-java example module —
+the published package is shared).
+
+## Running the example
+
+```console
+./gradlew :swift-java-ui-showcase-showcase-app:assembleDebug
+```
+
+or open the repository in Android Studio and run the
+`swift-java-ui-showcase-showcase-app` configuration on an emulator or device.
+
+To iterate on the Swift model without an Android device, the package is plain
+Swift — build and test it on your host machine:
+
+```console
+cd swift-java-ui-showcase/showcase-lib
+swift test
+```
+
+## JSON schema
+
+The wire format between Swift and Kotlin. Every component is a flat JSON
+object discriminated by `"kind"`; the schema is pinned by
+`buttonsScreenSchemaIsStable()` in
+`showcase-lib/Tests/ShowcaseKitTests/ShowcaseKitTests.swift` — update this
+table and that test together.
+
+`showcaseScreens()` returns `{"screens": [{"id", "title"}, ...]}`.
+`showcaseScreen(id)` and `showcaseDispatch(...)` return
+`{"id", "title", "components": [...]}` where each component is:
+
+| `kind` | Keys | Actions it emits |
+|---|---|---|
+| `sectionHeader` | `id`, `text` | — |
+| `text` | `id`, `text` | — |
+| `button` | `id`, `label`, `role` (`primary`\|`secondary`) | `{"type":"tap"}` |
+| `toggle` | `id`, `label`, `isOn` | `{"type":"setBool","value":…}` |
+| `checkbox` | `id`, `label`, `isChecked` | `{"type":"setBool","value":…}` |
+| `radioGroup` | `id`, `label`, `options`, `selectedIndex` (nullable) | `{"type":"select","index":…}` |
+| `segmentedControl` | `id`, `label`, `options`, `selectedIndex` | `{"type":"select","index":…}` |
+| `slider` | `id`, `label`, `value`, `min`, `max` | `{"type":"setNumber","value":…}` |
+| `progressIndicator` | `id`, `label`, `value` (`0.0`–`1.0`) | — (display-only) |
+| `stepper` | `id`, `label`, `value`, `min`, `max` (all `Int`) | `{"type":"setNumber","value":±1}` (a delta, not the new value) |
+| `datePicker` | `id`, `label`, `date` (`"yyyy-MM-dd"`) | `{"type":"setString","value":…}` |
+| `alert` | `id`, `title`, `message`, `confirmLabel`, `cancelLabel` | `{"type":"select","index":0}` (confirm) or `{"type":"select","index":1}` (cancel/dismiss) |
+| `textField` | `id`, `label`, `text`, `placeholder`, `keyboard` (`text`\|`email`\|`number`), `error` (nullable) | `{"type":"setString","value":…}` |
+| `textEditor` | `id`, `label`, `text`, `placeholder` | `{"type":"setString","value":…}` |
+| `code` | `id`, `title`, `code` | — (opens a fullscreen modal with Copy and Wrap actions; modal visibility and wrap state stay Kotlin-local) |
+
+## Add your own screen (~20 lines, no Kotlin)
+
+Conform to `ScreenDefinition` in its own file under
+`showcase-lib/Sources/ShowcaseKit/` (one screen per file, e.g. `ButtonsScreen.swift`):
+
+```swift
+final class GreetingScreen: ScreenDefinition {
+  let id = "greeting"
+  let title = "Greeting"
+
+  private var name = ""
+
+  func reduce(_ action: Action, componentId: String) {
+    if case .setString(let value) = action, componentId == "name" { name = value }
+  }
+
+  func body() -> [Component] {
+    [
+      .textField(id: "name", label: "Your name", text: name,
+                 placeholder: "World", keyboard: .text, error: nil),
+      .text(id: "greeting", text: "Hello, \(name.isEmpty ? "World" : name)!"),
+    ]
+  }
+}
+```
+
+then append `GreetingScreen()` to `defaultScreens()` in `ScreenRegistry.swift`.
+That's it — the home list and navigation are data-driven from Swift's
+registry, so the new screen appears with no Kotlin changes.
+
+## Add your own component kind
+
+Four touch points:
+
+1. A new case on `Component` in `showcase-lib/Sources/ShowcaseKit/Component.swift`
+2. Its `encode(to:)` / `init(from:)` clauses in the same file
+3. A new branch in the `when` in `showcase-app/.../ComponentRenderer.kt`
+4. A row in the schema table above (and, if you change existing shapes, the
+   pinned-schema test)
+
+## Troubleshooting
+
+See the [hello-swift-java troubleshooting section](../hello-swift-java/README.md#troubleshooting).
+The two paths in `showcase-lib/build.gradle` that hardcode the Swift target
+name (`Sources/ShowcaseKit` and the JExtract generated-java output directory)
+are the usual suspects if generated Java classes are missing or stale after
+renaming things.

swift-java-ui-showcase/showcase-app/.gitignore

@@ -0,0 +1 @@
+/build

swift-java-ui-showcase/showcase-app/build.gradle.kts

@@ -0,0 +1,75 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2026 Apple Inc. and the Swift.org project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of Swift.org project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+plugins {
+    alias(libs.plugins.android.application)
+    alias(libs.plugins.kotlin.android)
+    alias(libs.plugins.kotlin.compose)
+}
+
+android {
+    namespace = "com.example.showcaseapp"
+    compileSdk = 36
+
+    defaultConfig {
+        applicationId = "com.example.showcaseapp"
+        minSdk = 28
+        targetSdk = 36
+        versionCode = 1
+        versionName = "1.0"
+
+        testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
+    }
+
+    buildTypes {
+        release {
+            isMinifyEnabled = false
+            proguardFiles(
+                getDefaultProguardFile("proguard-android-optimize.txt"),
+                "proguard-rules.pro"
+            )
+        }
+    }
+    compileOptions {
+        sourceCompatibility = JavaVersion.VERSION_17
+        targetCompatibility = JavaVersion.VERSION_17
+    }
+    kotlinOptions {
+        jvmTarget = "17"
+    }
+    buildFeatures {
+        compose = true
+    }
+}
+
+dependencies {
+    implementation(libs.androidx.core.ktx)
+    implementation(libs.androidx.lifecycle.runtime.ktx)
+    implementation(libs.androidx.activity.compose)
+    implementation(platform(libs.androidx.compose.bom))
+    implementation(libs.androidx.ui)
+    implementation(libs.androidx.ui.graphics)
+    implementation(libs.androidx.ui.tooling.preview)
+    implementation(libs.androidx.material3)
+    implementation(libs.androidx.navigation.compose)
+    implementation("org.swift.swiftkit:swiftkit-core:+")
+    implementation(project(":swift-java-ui-showcase-showcase-lib"))
+    testImplementation(libs.junit)
+    androidTestImplementation(libs.androidx.junit)
+    androidTestImplementation(libs.androidx.espresso.core)
+    androidTestImplementation(platform(libs.androidx.compose.bom))
+    androidTestImplementation(libs.androidx.ui.test.junit4)
+    debugImplementation(libs.androidx.ui.tooling)
+    debugImplementation(libs.androidx.ui.test.manifest)
+}

swift-java-ui-showcase/showcase-app/proguard-rules.pro

@@ -0,0 +1,21 @@
+# Add project specific ProGuard rules here.
+# You can control the set of applied configuration files using the
+# proguardFiles setting in build.gradle.
+#
+# For more details, see
+#   http://developer.android.com/guide/developing/tools/proguard.html
+
+# If your project uses WebView with JS, uncomment the following
+# and specify the fully qualified class name to the JavaScript interface
+# class:
+#-keepclassmembers class fqcn.of.javascript.interface.for.webview {
+#   public *;
+#}
+
+# Uncomment this to preserve the line number information for
+# debugging stack traces.
+#-keepattributes SourceFile,LineNumberTable
+
+# If you keep the line number information, uncomment this to
+# hide the original source file name.
+#-renamesourcefileattribute SourceFile

swift-java-ui-showcase/showcase-app/src/androidTest/java/com/example/showcaseapp/ExampleInstrumentedTest.kt

@@ -0,0 +1,38 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2026 Apple Inc. and the Swift.org project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of Swift.org project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+package com.example.showcaseapp
+
+import androidx.test.platform.app.InstrumentationRegistry
+import androidx.test.ext.junit.runners.AndroidJUnit4
+
+import org.junit.Test
+import org.junit.runner.RunWith
+
+import org.junit.Assert.*
+
+/**
+ * Instrumented test, which will execute on an Android device.
+ *
+ * See [testing documentation](http://d.android.com/tools/testing).
+ */
+@RunWith(AndroidJUnit4::class)
+class ExampleInstrumentedTest {
+    @Test
+    fun useAppContext() {
+        // Context of the app under test.
+        val appContext = InstrumentationRegistry.getInstrumentation().targetContext
+        assertEquals("com.example.showcaseapp", appContext.packageName)
+    }
+}