Add a simple stacknav demo

demos/stack-nav/build.gradle.kts

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+/*
+ * Copyright (C) 2025. Uber Technologies
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+plugins {
+    id("ribs.android.application")
+}
+
+android {
+    namespace = "com.uber.rib.stacknav"
+
+    defaultConfig {
+        applicationId = "com.uber.rib.stacknav"
+        targetSdk = 36
+    }
+}
+
+dependencies {
+    implementation(project(":libraries:rib-android"))
+    implementation(project(":libraries:rib-router-navigator"))
+    implementation(libs.androidx.appcompat)
+}

demos/stack-nav/src/main/AndroidManifest.xml

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+<?xml version="1.0" encoding="utf-8"?>
+<manifest xmlns:android="http://schemas.android.com/apk/res/android">
+
+    <application
+        android:allowBackup="false"
+        android:icon="@drawable/ub__ic_launcher"
+        android:label="@string/app_name"
+        android:theme="@style/AppTheme">
+        <activity
+            android:name="com.uber.rib.stacknav.RootActivity"
+            android:exported="true">
+            <intent-filter>
+                <action android:name="android.intent.action.MAIN"/>
+                <category android:name="android.intent.category.LAUNCHER"/>
+            </intent-filter>
+        </activity>
+    </application>
+</manifest>

demos/stack-nav/src/main/kotlin/com/uber/rib/stacknav/RootActivity.kt

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+/*
+ * Copyright (C) 2025. Uber Technologies
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.uber.rib.stacknav
+
+import android.view.ViewGroup
+import com.uber.rib.core.RibActivity
+import com.uber.rib.core.ViewRouter
+import com.uber.rib.stacknav.root.RootInteractor
+import com.uber.rib.stacknav.root.RootRouter
+import com.uber.rib.stacknav.root.RootView
+
+class RootActivity : RibActivity() {
+
+  override fun createRouter(parentViewGroup: ViewGroup): ViewRouter<*, *> {
+    val rootView = RootView(this)
+    val interactor = RootInteractor()
+    return RootRouter(rootView, interactor)
+  }
+}

demos/stack-nav/src/main/kotlin/com/uber/rib/stacknav/root/RootInteractor.kt

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+/*
+ * Copyright (C) 2025. Uber Technologies
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.uber.rib.stacknav.root
+
+import com.uber.rib.core.Bundle
+import com.uber.rib.core.EmptyPresenter
+import com.uber.rib.core.Interactor
+import com.uber.rib.stacknav.root.screen.ScreenInteractor
+
+/**
+ * Orchestrates the navigation stack. Pushes the first screen on start, and reacts to each screen's
+ * request to push the next one.
+ */
+class RootInteractor :
+  Interactor<EmptyPresenter, RootRouter>(EmptyPresenter()), ScreenInteractor.Listener {
+
+  override fun didBecomeActive(savedInstanceState: Bundle?) {
+    super.didBecomeActive(savedInstanceState)
+    router.pushScreen(1)
+  }
+
+  override fun onPushNextScreen(currentNumber: Int) {
+    if (currentNumber < MAX_SCREENS) {
+      router.pushScreen(currentNumber + 1)
+    }
+  }
+
+  override fun onBackRequested() {
+    router.popScreen()
+  }
+
+  companion object {
+    const val MAX_SCREENS = 5
+  }
+}

demos/stack-nav/src/main/kotlin/com/uber/rib/stacknav/root/RootRouter.kt

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+/*
+ * Copyright (C) 2025. Uber Technologies
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.uber.rib.stacknav.root
+
+import com.uber.rib.core.BasicViewRouter
+import com.uber.rib.core.RouterNavigator
+import com.uber.rib.core.StackRouterNavigator
+import com.uber.rib.stacknav.root.screen.ScreenInteractor
+import com.uber.rib.stacknav.root.screen.ScreenRouter
+import com.uber.rib.stacknav.root.screen.ScreenView
+
+/**
+ * Manages the screen stack using [StackRouterNavigator]. Each call to [pushScreen] pushes a new
+ * [ScreenRouter] on top; [handleBackPress] pops it.
+ */
+class RootRouter(
+  view: RootView,
+  interactor: RootInteractor,
+) : BasicViewRouter<RootView, RootInteractor>(view, interactor) {
+
+  private val navigator: RouterNavigator<ScreenState> = StackRouterNavigator(this)
+
+  fun pushScreen(number: Int) {
+    val listener = interactor as ScreenInteractor.Listener
+    navigator.pushState(
+      ScreenState(number),
+      object : RouterNavigator.AttachTransition<ScreenRouter, ScreenState> {
+        override fun buildRouter(): ScreenRouter {
+          val screenView = ScreenView(view.context, number, RootInteractor.MAX_SCREENS)
+          return ScreenRouter(screenView, ScreenInteractor(number, listener))
+        }
+
+        override fun willAttachToHost(
+          router: ScreenRouter,
+          previousState: ScreenState?,
+          newState: ScreenState,
+          isPush: Boolean,
+        ) {
+          view.addView(
+            router.view,
+            android.view.ViewGroup.LayoutParams(
+              android.view.ViewGroup.LayoutParams.MATCH_PARENT,
+              android.view.ViewGroup.LayoutParams.MATCH_PARENT,
+            ),
+          )
+        }
+      },
+      object : RouterNavigator.DetachTransition<ScreenRouter, ScreenState> {
+        override fun willDetachFromHost(
+          router: ScreenRouter,
+          previousState: ScreenState,
+          newState: ScreenState?,
+          isPush: Boolean,
+        ) {
+          view.removeView(router.view)
+        }
+      },
+    )
+  }
+
+  override fun handleBackPress(): Boolean {
+    if (navigator.size() > 1) {
+      navigator.popState()
+      return true
+    }
+    return false
+  }
+
+  fun popScreen() {
+    navigator.popState()
+  }
+
+  override fun willDetach() {
+    navigator.hostWillDetach()
+    super.willDetach()
+  }
+}

demos/stack-nav/src/main/kotlin/com/uber/rib/stacknav/root/RootView.kt

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+/*
+ * Copyright (C) 2025. Uber Technologies
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.uber.rib.stacknav.root
+
+import android.content.Context
+import android.widget.FrameLayout
+
+/** Container that holds whichever screen is currently on top of the stack. */
+class RootView(context: Context) : FrameLayout(context)

demos/stack-nav/src/main/kotlin/com/uber/rib/stacknav/root/ScreenState.kt

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+/*
+ * Copyright (C) 2025. Uber Technologies
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.uber.rib.stacknav.root
+
+import com.uber.rib.core.RouterNavigatorState
+
+/** One entry in the navigation stack, identified by screen number. */
+data class ScreenState(val number: Int) : RouterNavigatorState {
+  override fun stateName() = "screen_$number"
+}

demos/stack-nav/src/main/kotlin/com/uber/rib/stacknav/root/screen/ScreenInteractor.kt

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+/*
+ * Copyright (C) 2025. Uber Technologies
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.uber.rib.stacknav.root.screen
+
+import com.uber.rib.core.Bundle
+import com.uber.rib.core.EmptyPresenter
+import com.uber.rib.core.Interactor
+
+/**
+ * Interactor for a single screen. Wires the view's button to [Listener.onPushNextScreen] and cleans
+ * up on deactivation to avoid leaks.
+ */
+class ScreenInteractor(
+  private val screenNumber: Int,
+  private val listener: Listener,
+) : Interactor<EmptyPresenter, ScreenRouter>(EmptyPresenter()) {
+
+  interface Listener {
+    fun onPushNextScreen(currentNumber: Int)
+    fun onBackRequested()
+  }
+
+  override fun didBecomeActive(savedInstanceState: Bundle?) {
+    super.didBecomeActive(savedInstanceState)
+    router.view.onNextClicked = { listener.onPushNextScreen(screenNumber) }
+    router.view.onBackClicked = { listener.onBackRequested() }
+  }
+
+  override fun willResignActive() {
+    router.view.onNextClicked = null
+    router.view.onBackClicked = null
+    super.willResignActive()
+  }
+}

demos/stack-nav/src/main/kotlin/com/uber/rib/stacknav/root/screen/ScreenRouter.kt

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+/*
+ * Copyright (C) 2025. Uber Technologies
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.uber.rib.stacknav.root.screen
+
+import com.uber.rib.core.BasicViewRouter
+
+/** Leaf router for a single numbered screen. No children. */
+class ScreenRouter(
+  view: ScreenView,
+  interactor: ScreenInteractor,
+) : BasicViewRouter<ScreenView, ScreenInteractor>(view, interactor)