Add PreviousButtonState and NextButtonState to ui-compose

* Provide a helper Composable for remembering the state instance and launching the listening coroutine that observes the changes in the Player
* Add an example to demo-compose of using Previous- and Next- ButtonStates inside a Previous- and NextButton Composable.
* Reformat the MainActivity usage of `Previous`, `PlayPause`, `Next` buttons to form Minimal Player Controls

PiperOrigin-RevId: 691943147

RELEASENOTES.md

@@ -57,8 +57,10 @@
 *   IMA extension:
 *   UI:
     *   Add `PlayerSurface` Composable to `media3-ui-compose` module.
-    *   Add `PlayPauseButtonState` class and `rememberPlayPauseButtonState`
-        Composable to `media3-ui-compose` module.
+    *   Add `PlayPauseButtonState`, `NextButtonState`, `PreviousButtonState`
+        classes and the corresponding `rememberPlayPauseButtonState`,
+        `rememberNextButtonState`, `rememberPreviousButtonState` Composables to
+        `media3-ui-compose` module.
 *   Downloads:
 *   OkHttp Extension:
 *   Cronet Extension:
@@ -76,8 +78,9 @@
 *   Cast Extension:
 *   Test Utilities:
 *   Demo app:
-    *   Add `PlayPauseButton` Composable UI element to `demo-compose` utilizing
-        `PlayPauseButtonState`.
+    *   Add `PlayPauseButton`, `NextButton`, `PreviousButton` and
+        `MinimalControls` Composable UI elements to `demo-compose` utilizing
+        `PlayPauseButtonState`, `NextButtonState`, and `PreviousButtonState`.
 *   Remove deprecated symbols:
     *   Remove deprecated `AudioMixer.create()` method. Use
         `DefaultAudioMixer.Factory().create()` instead.

demos/compose/src/main/java/androidx/media3/demo/compose/MainActivity.kt

@@ -19,18 +19,22 @@ import android.os.Bundle
 import androidx.activity.ComponentActivity
 import androidx.activity.compose.setContent
 import androidx.activity.enableEdgeToEdge
+import androidx.compose.foundation.clickable
+import androidx.compose.foundation.interaction.MutableInteractionSource
 import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.fillMaxSize
-import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.layout.navigationBarsPadding
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.platform.LocalContext
-import androidx.compose.ui.unit.dp
 import androidx.media3.common.MediaItem
 import androidx.media3.common.Player
-import androidx.media3.demo.compose.buttons.PlayPauseButton
+import androidx.media3.demo.compose.buttons.MinimalControls
 import androidx.media3.demo.compose.data.videos
 import androidx.media3.exoplayer.ExoPlayer
 import androidx.media3.ui.compose.PlayerSurface
@@ -45,21 +49,35 @@ class MainActivity : ComponentActivity() {
       val context = LocalContext.current
       val exoPlayer = remember {
         ExoPlayer.Builder(context).build().apply {
-          setMediaItem(MediaItem.fromUri(videos[0]))
+          setMediaItems(videos.map { MediaItem.fromUri(it) })
           prepare()
-          playWhenReady = true
-          repeatMode = Player.REPEAT_MODE_ONE
         }
       }
-      MediaPlayerScreen(player = exoPlayer, modifier = Modifier.fillMaxSize())
+      MediaPlayerScreen(
+        player = exoPlayer,
+        modifier = Modifier.fillMaxSize().navigationBarsPadding(),
+      )
     }
   }
 
   @Composable
   private fun MediaPlayerScreen(player: Player, modifier: Modifier = Modifier) {
+    var showControls by remember { mutableStateOf(true) }
     Box(modifier) {
-      PlayerSurface(player = player, surfaceType = SURFACE_TYPE_SURFACE_VIEW)
-      PlayPauseButton(player, Modifier.align(Alignment.Center).size(100.dp))
+      PlayerSurface(
+        player = player,
+        surfaceType = SURFACE_TYPE_SURFACE_VIEW,
+        modifier =
+          modifier.clickable(
+            interactionSource = remember { MutableInteractionSource() },
+            indication = null, // to prevent the ripple from the tap
+          ) {
+            showControls = !showControls
+          },
+      )
+      if (showControls) {
+        MinimalControls(player, Modifier.align(Alignment.Center))
+      }
     }
   }
 }

demos/compose/src/main/java/androidx/media3/demo/compose/buttons/MinimalControls.kt

@@ -0,0 +1,51 @@
+/*
+ * Copyright 2024 The Android Open Source Project
+ *
+ * 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
+ *
+ *      https://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 androidx.media3.demo.compose.buttons
+
+import androidx.compose.foundation.background
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.shape.CircleShape
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.unit.dp
+import androidx.media3.common.Player
+
+/**
+ * Minimal playback controls for a [Player].
+ *
+ * Includes buttons for seeking to a previous/next items or playing/pausing the playback.
+ */
+@Composable
+internal fun MinimalControls(player: Player, modifier: Modifier = Modifier) {
+  val graySemiTransparentBackground = Color.Gray.copy(alpha = 0.4f)
+  val modifierForIconButton =
+    modifier.size(80.dp).background(graySemiTransparentBackground, CircleShape)
+  Row(
+    modifier = modifier.fillMaxWidth(),
+    horizontalArrangement = Arrangement.SpaceEvenly,
+    verticalAlignment = Alignment.CenterVertically,
+  ) {
+    PreviousButton(player, modifierForIconButton)
+    PlayPauseButton(player, modifierForIconButton)
+    NextButton(player, modifierForIconButton)
+  }
+}

demos/compose/src/main/java/androidx/media3/demo/compose/buttons/NextButton.kt

@@ -0,0 +1,40 @@
+/*
+ * Copyright 2024 The Android Open Source Project
+ *
+ * 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
+ *
+ *      https://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 androidx.media3.demo.compose.buttons
+
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.filled.SkipNext
+import androidx.compose.material3.Icon
+import androidx.compose.material3.IconButton
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.res.stringResource
+import androidx.media3.common.Player
+import androidx.media3.demo.compose.R
+import androidx.media3.ui.compose.state.rememberNextButtonState
+
+@Composable
+internal fun NextButton(player: Player, modifier: Modifier = Modifier) {
+  val state = rememberNextButtonState(player)
+  IconButton(onClick = state::onClick, modifier = modifier, enabled = state.isEnabled) {
+    Icon(
+      Icons.Default.SkipNext,
+      contentDescription = stringResource(R.string.next_button),
+      modifier = modifier,
+    )
+  }
+}

demos/compose/src/main/java/androidx/media3/demo/compose/buttons/PlayPauseButton.kt

@@ -17,8 +17,8 @@
 package androidx.media3.demo.compose.buttons
 
 import androidx.compose.material.icons.Icons
-import androidx.compose.material.icons.filled.PauseCircle
-import androidx.compose.material.icons.filled.PlayCircle
+import androidx.compose.material.icons.filled.Pause
+import androidx.compose.material.icons.filled.PlayArrow
 import androidx.compose.material3.Icon
 import androidx.compose.material3.IconButton
 import androidx.compose.runtime.Composable
@@ -31,7 +31,7 @@ import androidx.media3.ui.compose.state.rememberPlayPauseButtonState
 @Composable
 internal fun PlayPauseButton(player: Player, modifier: Modifier = Modifier) {
   val state = rememberPlayPauseButtonState(player)
-  val icon = if (state.showPlay) Icons.Default.PlayCircle else Icons.Default.PauseCircle
+  val icon = if (state.showPlay) Icons.Default.PlayArrow else Icons.Default.Pause
   val contentDescription =
     if (state.showPlay) stringResource(R.string.playpause_button_play)
     else stringResource(R.string.playpause_button_pause)

demos/compose/src/main/java/androidx/media3/demo/compose/buttons/PreviousButton.kt

@@ -0,0 +1,40 @@
+/*
+ * Copyright 2024 The Android Open Source Project
+ *
+ * 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
+ *
+ *      https://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 androidx.media3.demo.compose.buttons
+
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.filled.SkipPrevious
+import androidx.compose.material3.Icon
+import androidx.compose.material3.IconButton
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.res.stringResource
+import androidx.media3.common.Player
+import androidx.media3.demo.compose.R
+import androidx.media3.ui.compose.state.rememberPreviousButtonState
+
+@Composable
+internal fun PreviousButton(player: Player, modifier: Modifier = Modifier) {
+  val state = rememberPreviousButtonState(player)
+  IconButton(onClick = state::onClick, modifier = modifier, enabled = state.isEnabled) {
+    Icon(
+      Icons.Default.SkipPrevious,
+      contentDescription = stringResource(R.string.previous_button),
+      modifier = modifier,
+    )
+  }
+}

demos/compose/src/main/java/androidx/media3/demo/compose/data/videos.kt

@@ -18,6 +18,5 @@ package androidx.media3.demo.compose.data
 val videos =
   listOf(
     "https://html5demos.com/assets/dizzy.mp4",
-    "https://devstreaming-cdn.apple.com/videos/streaming/examples/bipbop_4x3/gear0/fileSequence0.aac",
     "https://storage.googleapis.com/exoplayer-test-media-1/gen-3/screens/dash-vod-single-segment/video-vp9-360.webm",
   )

demos/compose/src/main/res/values/strings.xml

@@ -17,4 +17,6 @@
   <string name="app_name">Media3 Compose Demo</string>
   <string name="playpause_button_play">Play</string>
   <string name="playpause_button_pause">Pause</string>
+  <string name="next_button">Next</string>
+  <string name="previous_button">Previous</string>
 </resources>

libraries/ui_compose/src/main/java/androidx/media3/ui/compose/state/NextButtonState.kt

@@ -0,0 +1,65 @@
+/*
+ * Copyright 2024 The Android Open Source Project
+ *
+ * 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
+ *
+ *      https://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 androidx.media3.ui.compose.state
+
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.LaunchedEffect
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
+import androidx.media3.common.Player
+import androidx.media3.common.listen
+import androidx.media3.common.util.UnstableApi
+
+/**
+ * Remembers the value of [NextButtonState] created based on the passed [Player] and launch a
+ * coroutine to listen to [Player]'s changes. If the [Player] instance changes between compositions,
+ * produce and remember a new value.
+ */
+@UnstableApi
+@Composable
+fun rememberNextButtonState(player: Player): NextButtonState {
+  val nextButtonState = remember(player) { NextButtonState(player) }
+  LaunchedEffect(player) { nextButtonState.observe() }
+  return nextButtonState
+}
+
+/**
+ * State that holds all interactions to correctly deal with a UI component representing a
+ * seek-to-next button.
+ *
+ * This button has no internal state to maintain, it can only be enabled or disabled.
+ *
+ * @property[isEnabled] determined by `isCommandAvailable(Player.COMMAND_SEEK_TO_NEXT)`
+ */
+@UnstableApi
+class NextButtonState(private val player: Player) {
+  var isEnabled by mutableStateOf(player.isCommandAvailable(Player.COMMAND_SEEK_TO_NEXT))
+    private set
+
+  fun onClick() {
+    player.seekToNext()
+  }
+
+  suspend fun observe(): Nothing =
+    player.listen { events ->
+      if (events.contains(Player.EVENT_AVAILABLE_COMMANDS_CHANGED)) {
+        isEnabled = isCommandAvailable(Player.COMMAND_SEEK_TO_NEXT)
+      }
+    }
+}

libraries/ui_compose/src/main/java/androidx/media3/ui/compose/state/PreviousButtonState.kt

@@ -0,0 +1,65 @@
+/*
+ * Copyright 2024 The Android Open Source Project
+ *
+ * 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
+ *
+ *      https://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 androidx.media3.ui.compose.state
+
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.LaunchedEffect
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
+import androidx.media3.common.Player
+import androidx.media3.common.listen
+import androidx.media3.common.util.UnstableApi
+
+/**
+ * Remembers the value of [PreviousButtonState] created based on the passed [Player] and launch a
+ * coroutine to listen to [Player]'s changes. If the [Player] instance changes between compositions,
+ * produce and remember a new value.
+ */
+@UnstableApi
+@Composable
+fun rememberPreviousButtonState(player: Player): PreviousButtonState {
+  val previousButtonState = remember(player) { PreviousButtonState(player) }
+  LaunchedEffect(player) { previousButtonState.observe() }
+  return previousButtonState
+}
+
+/**
+ * State that holds all interactions to correctly deal with a UI component representing a
+ * seek-to-previous button.
+ *
+ * This button has no internal state to maintain, it can only be enabled or disabled.
+ *
+ * @property[isEnabled] determined by `isCommandAvailable(Player.COMMAND_SEEK_TO_PREVIOUS)`
+ */
+@UnstableApi
+class PreviousButtonState(private val player: Player) {
+  var isEnabled by mutableStateOf(player.isCommandAvailable(Player.COMMAND_SEEK_TO_PREVIOUS))
+    private set
+
+  fun onClick() {
+    player.seekToPrevious()
+  }
+
+  suspend fun observe(): Nothing =
+    player.listen { events ->
+      if (events.contains(Player.EVENT_AVAILABLE_COMMANDS_CHANGED)) {
+        isEnabled = isCommandAvailable(Player.COMMAND_SEEK_TO_PREVIOUS)
+      }
+    }
+}

libraries/ui_compose/src/test/java/androidx/media3/ui/compose/state/NextButtonStateTest.kt

@@ -0,0 +1,99 @@
+/*
+ * Copyright 2024 The Android Open Source Project
+ *
+ * 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
+ *
+ *      https://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 androidx.media3.ui.compose.state
+
+import androidx.compose.ui.test.junit4.createComposeRule
+import androidx.media3.common.Player
+import androidx.media3.ui.compose.utils.TestPlayer
+import androidx.test.ext.junit.runners.AndroidJUnit4
+import com.google.common.truth.Truth.assertThat
+import org.junit.Rule
+import org.junit.Test
+import org.junit.runner.RunWith
+
+/** Unit test for [NextButtonState]. */
+@RunWith(AndroidJUnit4::class)
+class NextButtonStateTest {
+
+  @get:Rule val composeTestRule = createComposeRule()
+
+  @Test
+  fun addSeekNextCommandToPlayer_buttonStateTogglesFromDisabledToEnabled() {
+    val player = TestPlayer()
+    player.playbackState = Player.STATE_READY
+    player.playWhenReady = true
+    player.removeCommands(Player.COMMAND_SEEK_TO_NEXT)
+
+    lateinit var state: NextButtonState
+    composeTestRule.setContent { state = rememberNextButtonState(player = player) }
+
+    assertThat(state.isEnabled).isFalse()
+
+    player.addCommands(Player.COMMAND_SEEK_TO_NEXT)
+    composeTestRule.waitForIdle()
+
+    assertThat(state.isEnabled).isTrue()
+  }
+
+  @Test
+  fun removeSeekNextCommandToPlayer_buttonStateTogglesFromEnabledToDisabled() {
+    val player = TestPlayer()
+    player.playbackState = Player.STATE_READY
+    player.playWhenReady = true
+
+    lateinit var state: NextButtonState
+    composeTestRule.setContent { state = rememberNextButtonState(player = player) }
+
+    assertThat(state.isEnabled).isTrue()
+
+    player.removeCommands(Player.COMMAND_SEEK_TO_NEXT)
+    composeTestRule.waitForIdle()
+
+    assertThat(state.isEnabled).isFalse()
+  }
+
+  @Test
+  fun clickNextOnPenultimateMediaItem_buttonStateTogglesFromEnabledToDisabled() {
+    val player = TestPlayer()
+    player.playbackState = Player.STATE_READY
+    player.playWhenReady = true
+
+    lateinit var state: NextButtonState
+    composeTestRule.setContent { state = rememberNextButtonState(player = player) }
+
+    assertThat(state.isEnabled).isTrue()
+
+    player.seekToNext()
+    composeTestRule.waitForIdle()
+
+    assertThat(state.isEnabled).isFalse()
+  }
+
+  @Test
+  fun playerInReadyState_buttonClicked_nextItemPlaying() {
+    val player = TestPlayer()
+    player.playbackState = Player.STATE_READY
+    player.playWhenReady = true
+    val state = NextButtonState(player)
+
+    assertThat(player.currentMediaItemIndex).isEqualTo(0)
+
+    state.onClick()
+
+    assertThat(player.currentMediaItemIndex).isEqualTo(1)
+  }
+}

libraries/ui_compose/src/test/java/androidx/media3/ui/compose/state/PlayPauseButtonStateTest.kt

@@ -16,15 +16,11 @@
 
 package androidx.media3.ui.compose.state
 
-import android.os.Looper
 import androidx.compose.ui.test.junit4.createComposeRule
 import androidx.media3.common.Player
-import androidx.media3.common.SimpleBasePlayer
+import androidx.media3.ui.compose.utils.TestPlayer
 import androidx.test.ext.junit.runners.AndroidJUnit4
-import com.google.common.collect.ImmutableList
 import com.google.common.truth.Truth.assertThat
-import com.google.common.util.concurrent.Futures
-import com.google.common.util.concurrent.ListenableFuture
 import org.junit.Rule
 import org.junit.Test
 import org.junit.runner.RunWith
@@ -133,74 +129,3 @@ class PlayPauseButtonStateTest {
     assertThat(player.playbackState).isEqualTo(Player.STATE_BUFFERING)
   }
 }
-
-private class TestPlayer : SimpleBasePlayer(Looper.myLooper()!!) {
-  private var state =
-    State.Builder()
-      .setAvailableCommands(Player.Commands.Builder().addAllCommands().build())
-      .setPlaylist(ImmutableList.of(MediaItemData.Builder(/* uid= */ Any()).build()))
-      .build()
-
-  override fun getState(): State {
-    return state
-  }
-
-  override fun handleSetPlayWhenReady(playWhenReady: Boolean): ListenableFuture<*> {
-    state =
-      state
-        .buildUpon()
-        .setPlayWhenReady(playWhenReady, PLAY_WHEN_READY_CHANGE_REASON_USER_REQUEST)
-        .build()
-    return Futures.immediateVoidFuture()
-  }
-
-  override fun handlePrepare(): ListenableFuture<*> {
-    state =
-      state
-        .buildUpon()
-        .setPlayerError(null)
-        .setPlaybackState(if (state.timeline.isEmpty) STATE_ENDED else STATE_BUFFERING)
-        .build()
-    return Futures.immediateVoidFuture()
-  }
-
-  override fun handleSeek(
-    mediaItemIndex: Int,
-    positionMs: Long,
-    seekCommand: @Player.Command Int,
-  ): ListenableFuture<*> {
-    state =
-      state.buildUpon().setPlaybackState(STATE_BUFFERING).setContentPositionMs(positionMs).build()
-    return Futures.immediateVoidFuture()
-  }
-
-  fun setPlaybackState(playbackState: @Player.State Int) {
-    state = state.buildUpon().setPlaybackState(playbackState).build()
-    invalidateState()
-  }
-
-  fun setPosition(positionMs: Long) {
-    state = state.buildUpon().setContentPositionMs(positionMs).build()
-    invalidateState()
-  }
-
-  fun removeCommands(vararg commands: @Player.Command Int) {
-    state =
-      state
-        .buildUpon()
-        .setAvailableCommands(
-          Player.Commands.Builder().addAllCommands().removeAll(*commands).build()
-        )
-        .build()
-    invalidateState()
-  }
-
-  fun addCommands(vararg commands: @Player.Command Int) {
-    state =
-      state
-        .buildUpon()
-        .setAvailableCommands(Player.Commands.Builder().addAll(*commands).build())
-        .build()
-    invalidateState()
-  }
-}

libraries/ui_compose/src/test/java/androidx/media3/ui/compose/state/PreviousButtonStateTest.kt

@@ -0,0 +1,82 @@
+/*
+ * Copyright 2024 The Android Open Source Project
+ *
+ * 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
+ *
+ *      https://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 androidx.media3.ui.compose.state
+
+import androidx.compose.ui.test.junit4.createComposeRule
+import androidx.media3.common.Player
+import androidx.media3.ui.compose.utils.TestPlayer
+import androidx.test.ext.junit.runners.AndroidJUnit4
+import com.google.common.truth.Truth.assertThat
+import org.junit.Rule
+import org.junit.Test
+import org.junit.runner.RunWith
+
+/** Unit test for [PreviousButtonState]. */
+@RunWith(AndroidJUnit4::class)
+class PreviousButtonStateTest {
+
+  @get:Rule val composeTestRule = createComposeRule()
+
+  @Test
+  fun addSeekPrevCommandToPlayer_buttonStateTogglesFromDisabledToEnabled() {
+    val player = TestPlayer()
+    player.playbackState = Player.STATE_READY
+    player.playWhenReady = true
+    player.removeCommands(Player.COMMAND_SEEK_TO_PREVIOUS)
+
+    lateinit var state: PreviousButtonState
+    composeTestRule.setContent { state = rememberPreviousButtonState(player = player) }
+
+    assertThat(state.isEnabled).isFalse()
+
+    composeTestRule.runOnUiThread { player.addCommands(Player.COMMAND_SEEK_TO_PREVIOUS) }
+    composeTestRule.waitForIdle()
+
+    assertThat(state.isEnabled).isTrue()
+  }
+
+  @Test
+  fun removeSeekPrevCommandToPlayer_buttonStateTogglesFromEnabledToDisabled() {
+    val player = TestPlayer()
+    player.playbackState = Player.STATE_READY
+    player.playWhenReady = true
+
+    lateinit var state: PreviousButtonState
+    composeTestRule.setContent { state = rememberPreviousButtonState(player = player) }
+
+    assertThat(state.isEnabled).isTrue()
+
+    composeTestRule.runOnUiThread { player.removeCommands(Player.COMMAND_SEEK_TO_PREVIOUS) }
+    composeTestRule.waitForIdle()
+
+    assertThat(state.isEnabled).isFalse()
+  }
+
+  @Test
+  fun playerInReadyState_prevButtonClicked_sameItemPlayingFromBeginning() {
+    val player = TestPlayer()
+    player.playbackState = Player.STATE_READY
+    player.playWhenReady = true
+    val state = PreviousButtonState(player)
+
+    assertThat(player.currentMediaItemIndex).isEqualTo(0)
+
+    state.onClick()
+
+    assertThat(player.currentMediaItemIndex).isEqualTo(0)
+  }
+}

libraries/ui_compose/src/test/java/androidx/media3/ui/compose/utils/TestPlayer.kt

@@ -0,0 +1,113 @@
+/*
+ * Copyright 2024 The Android Open Source Project
+ *
+ * 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
+ *
+ *      https://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 androidx.media3.ui.compose.utils
+
+import android.os.Looper
+import androidx.media3.common.Player
+import androidx.media3.common.SimpleBasePlayer
+import com.google.common.collect.ImmutableList
+import com.google.common.util.concurrent.Futures
+import com.google.common.util.concurrent.ListenableFuture
+
+/**
+ * A fake [Player] that uses [SimpleBasePlayer]'s minimal number of default methods implementations
+ * to build upon to simulate realistic playback scenarios for testing.
+ */
+internal class TestPlayer : SimpleBasePlayer(Looper.myLooper()!!) {
+  private var state =
+    State.Builder()
+      .setAvailableCommands(Player.Commands.Builder().addAllCommands().build())
+      .setPlaylist(
+        ImmutableList.of(
+          MediaItemData.Builder(/* uid= */ "First").build(),
+          MediaItemData.Builder(/* uid= */ "Second").build(),
+        )
+      )
+      .setPlayWhenReady(true, PLAY_WHEN_READY_CHANGE_REASON_USER_REQUEST)
+      .build()
+
+  override fun getState(): State {
+    return state
+  }
+
+  override fun handleSetPlayWhenReady(playWhenReady: Boolean): ListenableFuture<*> {
+    state =
+      state
+        .buildUpon()
+        .setPlayWhenReady(playWhenReady, PLAY_WHEN_READY_CHANGE_REASON_USER_REQUEST)
+        .build()
+    return Futures.immediateVoidFuture()
+  }
+
+  override fun handlePrepare(): ListenableFuture<*> {
+    state =
+      state
+        .buildUpon()
+        .setPlayerError(null)
+        .setPlaybackState(if (state.timeline.isEmpty) STATE_ENDED else STATE_BUFFERING)
+        .build()
+    return Futures.immediateVoidFuture()
+  }
+
+  override fun handleSeek(
+    mediaItemIndex: Int,
+    positionMs: Long,
+    seekCommand: @Player.Command Int,
+  ): ListenableFuture<*> {
+    state =
+      state
+        .buildUpon()
+        .setPlaybackState(STATE_BUFFERING)
+        .setCurrentMediaItemIndex(mediaItemIndex)
+        .setContentPositionMs(positionMs)
+        .build()
+    if (mediaItemIndex == state.playlist.size - 1) {
+      removeCommands(Player.COMMAND_SEEK_TO_NEXT)
+    }
+    return Futures.immediateVoidFuture()
+  }
+
+  fun setPlaybackState(playbackState: @Player.State Int) {
+    state = state.buildUpon().setPlaybackState(playbackState).build()
+    invalidateState()
+  }
+
+  fun setPosition(positionMs: Long) {
+    state = state.buildUpon().setContentPositionMs(positionMs).build()
+    invalidateState()
+  }
+
+  fun removeCommands(vararg commands: @Player.Command Int) {
+    state =
+      state
+        .buildUpon()
+        .setAvailableCommands(
+          Player.Commands.Builder().addAllCommands().removeAll(*commands).build()
+        )
+        .build()
+    invalidateState()
+  }
+
+  fun addCommands(vararg commands: @Player.Command Int) {
+    state =
+      state
+        .buildUpon()
+        .setAvailableCommands(Player.Commands.Builder().addAll(*commands).build())
+        .build()
+    invalidateState()
+  }
+}