使用Jetpack Compose编写一款简单的AndroidTV应用

前言

我很好奇Jetpack Compose作为一个新的界面工具包，在TV端使用体验会如何，毕竟现有的leanback库并不是很好用，而且自定义难度很大，导致大多个人开源的TV项目都长得差不多；

随着正式版的发布，我想在被大浪卷走之前努力一下，学习Jetpack Compose并开发一款简单的TV端应用；

同时听取巨佬的建议-养成写文章的习惯对技能会有所提升，尝试写下这篇文章做些经验总结。

预览

项目地址：compose-anime-tv

喜欢的话，欢迎点个Star。

1. 副作用(Effect)

放在第一个说主要是我觉得副作用对Jetpack Compose真的很重要，不需要很了解，但一定要知道这是啥；

Jetpack Compose两大标签声明式与函数式，尤其是函数式是我们主要需要适应的；@Composable函数会根据UI刷新而重复运行，但是里面的一些如初始化、绑定等行为，或者是一些定义的变量，他们是不可以跟随UI刷新而重新初始化、重复绑定或重新生成的；

为了能让它们在合适的时间运行，就需要使用副作用Effect；

这里推荐下fundroid大佬的这篇文章，写得非常好，连（副作用）的命名都有解释；

Jetpack Compose Side Effect：如何处理副作用 @fundroid

2. 按键传递(KeyEvent)

为了尽量使用现有的Modifier扩展，我首先在官方文档查阅了下KeyEvent，看到了下面这段代码：

Box(
    Modifier
        .onPreviewKeyEvent { keyEvent1 -> false }
        // .onKeyEvent { keyEvent5 -> false }
        .onKeyEvent { keyEvent4 -> false }
) {
    Box(
        Modifier
            .onPreviewKeyEvent { keyEvent2 -> false }
            .onKeyEvent { keyEvent3 -> false }
            .focusable()
    )
}
复制代码

我非常喜欢上面这段代码，只有onKeyEvent()、onPreviewKeyEvent()两个扩展、而且基本能满足开发需要。

3. 焦点处理(Focus)

官方sample：androidx.compose.ui.samples.FocusableSample

3.1 Modifier扩展

主要为下面这几个：

- Modifier.focusTarget()、Modifier.focusable()
- Modifier.onFocusEvent()、Modifier.onFocusChange()
- Modifier.focusRequester()、Modifier.focusOrder()
复制代码

3.1.1 focusable()与focusTarget()

focusable()是对focusTarget()的进一步封装，必须配置focusTarget()才能获取焦点，正常使用onFocusChange()、onKeyEvent()等；

官方建议使用focusable()而不是直接使用focusTarget()，但是我在使用中遇到过下面这个错误，加上封装的功能我还不是很需要，所以项目中我还是主要使用了focusTarget()；

kotlin.UninitializedPropertyAccessException: lateinit property relocationRequesterNode has not been initialized
        at androidx.compose.ui.layout.RelocationRequesterModifier.getRelocationRequesterNode(RelocationRequesterModifier.kt:32)
        at androidx.compose.ui.layout.RelocationRequester.bringIntoView(RelocationRequester.kt:61)
        at androidx.compose.ui.layout.RelocationRequester.bringIntoView$default(RelocationRequester.kt:59)
        at androidx.compose.foundation.FocusableKt$focusable$2$4$1.invokeSuspend(Focusable.kt:108)
        at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
        at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:106)
        ...
复制代码

PS：focusTarget()曾经叫focusModifier()，我感觉旧名字更能体现为啥一定要配置了才能使用相关方法，所以这里提一下。

3.1.2 onFocusChange()与onFocusEvent()

onFocusEvent()作用是回调焦点状态FocusState；

interface FocusState {
    val isFocused: Boolean
    val hasFocus: Boolean
    val isCaptured: Boolean
}
复制代码

onFocusChange()则是对onFocusEvent()的封装，只有变化回调FocusState，类似于Flow.distinctUntilChanged；

一般onFocusChange()用的比较多；

3.1.3 focusOrder()与focusRequester()

focusRequester()用于给控件配置FocusRequester类：

class FocusRequester {
    fun requestFocus()
    fun captureFocus(): Boolean
    fun freeFocus(): Boolean
}
复制代码

FocusRequester.requestFocus()是给控件获取焦点的唯一手段;

captureFocus()和freeFocus()分别是锁定与释放焦点；

focusOrder()用于确定下一个获取焦点的控件：

@Composable
fun FocusOrderSample() {
  val (item1, item2, item3, item4) = remember { FocusRequester.createRefs() }
  Box(
    Modifier
      .focusOrder(item1) {
        next = item2
        right = item2
        down = item3
        previous = item4
      }
      .focusable()
  )
  ...
}
复制代码

官方为了便于focusOrder()使用，加了下面这个扩展，为此在项目里我偷懒了下，都使用了focusOrder()配置FocusRequester；

fun Modifier.focusOrder(focusRequester: FocusRequester): Modifier = focusRequester(focusRequester)
复制代码

简化一下，平时使用较多的Modifier扩展就减成了三大件：

focusTarget()、focusOrder()、onFocusChange()

3.2 FocusManager

interface FocusManager {
    fun clearFocus(force: Boolean)
    fun moveFocus(focusDirection: FocusDirection): Boolean
}
复制代码

通过LocalFocusManager.current获取，实现类FocusManagerImpl是私有的，同时内部很多变量也是私有的，不便于自定义FocusManager，能做的事情就比较有限了。

4. Jetpack Compose中的按键&焦点传递

进入AndroidComposeView，从dispatchKeyEvent()开始大致预览下实现：

androidx.compose.ui.platform.AndroidComposeView.android.kt

override fun dispatchKeyEvent(event: AndroidKeyEvent) =
    if (isFocused) {
        sendKeyEvent(KeyEvent(event))
    } else {
        super.dispatchKeyEvent(event)
    }

override fun sendKeyEvent(keyEvent: KeyEvent): Boolean {
    return keyInputModifier.processKeyInput(keyEvent)
}

private val keyInputModifier: KeyInputModifier = KeyInputModifier(
    onKeyEvent = {
        val focusDirection = getFocusDirection(it)
        if (focusDirection == null || it.type != KeyDown) return@KeyInputModifier false

        // Consume the key event if we moved focus.
        focusManager.moveFocus(focusDirection)
    },
    onPreviewKeyEvent = null
)

复制代码

androidx.compose.ui.input.key.KeyInputModifier.kt

internal class KeyInputModifier(
    val onKeyEvent: ((KeyEvent) -> Boolean)?,
    val onPreviewKeyEvent: ((KeyEvent) -> Boolean)?
) : Modifier.Element {
    lateinit var keyInputNode: ModifiedKeyInputNode

    fun processKeyInput(keyEvent: KeyEvent): Boolean {
        val activeKeyInputNode = keyInputNode.findPreviousFocusWrapper()
            ?.findActiveFocusNode()
            ?.findLastKeyInputWrapper()
            ?: error("KeyEvent can't be processed because this key input node is not active.")
        return with(activeKeyInputNode) {
            val consumed = propagatePreviewKeyEvent(keyEvent)
            if (consumed) true else propagateKeyEvent(keyEvent)
        }
    }
}

fun Modifier.onPreviewKeyEvent(onPreviewKeyEvent: (KeyEvent) -> Boolean): Modifier = composed {
    KeyInputModifier(onKeyEvent = null, onPreviewKeyEvent = onPreviewKeyEvent)
}

fun Modifier.onKeyEvent(onKeyEvent: (KeyEvent) -> Boolean): Modifier = composed {
    KeyInputModifier(onKeyEvent = onKeyEvent, onPreviewKeyEvent = null)
}
复制代码

上面的代码结合官方KeyEvent的使用示例，可以判断出：

Jetpack Compose会先把KeyEvent交给Focus链上配置了onKeyEvent()的控件们消费，没有控件消费就会走默认的onKeyEvent()，约等于focusManager.moveFocus(focusDirection)；

再看下focusManager是大致是怎么处理的：

androidx.compose.ui.focus.FocusManager

class FocusManagerImpl(
    private val focusModifier: FocusModifier = FocusModifier(Inactive)
) : FocusManager {
    ...
    override fun moveFocus(focusDirection: FocusDirection): Boolean {
        val source = focusModifier.focusNode.findActiveFocusNode() ?: return false
        
        val nextFocusRequester = source.customFocusSearch(focusDirection, layoutDirection)
        if (nextFocusRequester != FocusRequester.Default) {
            nextFocusRequester.requestFocus()
            return true
        }

        val destination = focusModifier.focusNode.focusSearch(focusDirection, layoutDirection)
        if (destination == null || destination == source) {
          return false
        }

        // We don't want moveFocus to set focus to the root, as this would essentially clear focus.
        if (destination.findParentFocusNode() == null) {
          return when (focusDirection) {
            // Skip the root and proceed to the next/previous item from the root's perspective.
            Next, Previous -> {
              destination.requestFocus(propagateFocus = false)
              moveFocus(focusDirection)
            }
            // Instead of moving out to the root, we return false.
            // When we return false the key event will not be consumed, but it will bubble
            // up to the owner. (In the case of Android, the back key will be sent to the
            // activity, where it can be handled appropriately).
            @OptIn(ExperimentalComposeUiApi::class)
            Out -> false
            else -> error("Move focus landed at the root through an unknown path.")
          }
        }

        // If we found a potential next item, call requestFocus() to move focus to it.
        destination.requestFocus(propagateFocus = false)
        return true
    }
}
复制代码

nextFocusRequester就是通过focusOrder配置的下一个目标，如果返回的不是FocusRequester.Default，就直接requestFocus()；

否则就通过focusModifier.focusNode.focusSearch()寻找焦点：

internal fun ModifiedFocusNode.focusSearch(
    focusDirection: FocusDirection,
    layoutDirection: LayoutDirection
): ModifiedFocusNode? {
    return when (focusDirection) {
        Next, Previous -> oneDimensionalFocusSearch(focusDirection)
        Left, Right, Up, Down -> twoDimensionalFocusSearch(focusDirection)
        @OptIn(ExperimentalComposeUiApi::class)
        In -> {
            // we search among the children of the active item.
            val direction = when (layoutDirection) { Rtl -> Left; Ltr -> Right }
            findActiveFocusNode()?.twoDimensionalFocusSearch(direction)
        }
        @OptIn(ExperimentalComposeUiApi::class)
        Out -> findActiveFocusNode()?.findParentFocusNode()
        else -> error(invalidFocusDirection)
    }
}

internal fun ModifiedFocusNode.findActiveFocusNode(): ModifiedFocusNode? {
    return when (focusState) {
        Active, Captured -> this
        ActiveParent -> focusedChild?.findActiveFocusNode()
        Inactive, Disabled -> null
    }
}
复制代码

findActiveFocusNode()方法主要还是确定当前的焦点，基于当前焦点去寻找下一个目标；

oneDimensionalFocusSearch()与twoDimensionalFocusSearch()都是往child寻找下一个目标，我想的传递方案和这个是相反的，所以这两个方法我没过多研究；

findParentFocusNode()则是把焦点传给parent，这个会是我比较常用的，我查了下这个方法的引用，目前好像只能通过focusManager.moveFocus(FocusDirection.Out)去触发；

做个小总结：

1. 基于focusOrder()确定下一个目标是最直接、最稳定的，不会走后面那些较为复杂的判断，上层方便配置的话尽量配置；
1. 虽然我很喜欢onKeyEvent()，但是onKeyEvent()初步看来只适合在Focus链的两端使用，不然很可能判断不足，把原本想让focusManager.moveFocus()消费的行为给抢走；
1. 可以通过focusManager.moveFocus(FocusDirection.Out)把当前焦点传给parent。

5. 焦点传递实践

我预期的传递方案大致就是：

每个组件各自处理焦点，焦点从最外层逐步传入；移动焦点时，当前组件不消费就传给父组件处理。

以示例来说，先自定义两个组件Box1与Box2：

@Composable
fun AppScreen() {
  val (focus1, focus2) = remember { FocusRequester.createRefs() }

  Row(
    modifier = Modifier.fillMaxSize(),
    horizontalArrangement = Arrangement.SpaceAround,
    verticalAlignment = Alignment.CenterVertically
  ) {
    Box1(Modifier.focusOrder(focus1) { 
      right = focus2 
      // left = focus2
    })
    Box2(Modifier.focusOrder(focus2) {
      left = focus1
      // right = focus1
    })
  }

  SideEffect {
    focus1.requestFocus()
  }
}

@Composable
fun Box1(modifier: Modifier = Modifier) {
  var isParentFocused by remember { mutableStateOf(false) }
  Box(
    modifier = modifier
      // .background(Color.Green)
      // .size(200.dp)
      .onFocusChanged { isParentFocused = it.isFocused }
      .focusTarget(),
    // contentAlignment = Alignment.Center
  ) {
    Text(
      if (isParentFocused) "Focused" else "",
      // color = Color.White,
      // style = MaterialTheme.typography.h3
    )
  }
}

@Composable
fun Box2(modifier: Modifier = Modifier) {
  ...
}
复制代码

其他不变的情况下，把Box1改成一个List：

@Composable
fun Box1(modifier: Modifier = Modifier) {
  var isParentFocused by remember { mutableStateOf(false) }
  var focusIndex by remember { mutableStateOf(0) }

  LazyColumn(
    modifier = modifier
      .onFocusChanged { isParentFocused = it.isFocused }
      .focusTarget(),
  ) {
    items(10) { index ->
      val focusRequester = remember { FocusRequester() }
      var isFocused by remember { mutableStateOf(false) }
      Text(
        if (isFocused) "Focused" else "",
        // color = Color.Black,
        // style = MaterialTheme.typography.h5,
        // textAlign = TextAlign.Center,
        modifier = Modifier
          // .padding(10.dp)
          // .background(Color.Green)
          // .width(120.dp)
          // .padding(vertical = 10.dp)
          .onFocusChanged {
            isFocused = it.isFocused
            if (isFocused) focusIndex = index
          }
          .focusOrder(focusRequester)
          .focusTarget(),
      )

      if (isParentFocused && focusIndex == index) {
        SideEffect {
          focusRequester.requestFocus()
        }
      }
    }
  }
}
复制代码

看似没什么问题，但其实向右的跳转并不是根据AppScreen中的配置而跳转的，给Box1配置focusOrder(focus1) { left = focus2 }，按左键并不能找到focus2；

这里就需要手动去把焦点传给parent，借助onKeyEvent()在按键传递过程中触发focusManager.moveFocus(FocusDirection.Out)把焦点返给parent，并返回false让这个按键继续传递下去;

...
val focusManager = LocalFocusManager.current
LazyColumn(
  modifier = modifier
    // .onFocusChanged { isParentFocused = it.isFocused }
    .onKeyEvent {
      when (it) {
        Key.DirectionRight,
        Key.DirectionLeft -> {
          focusManager.moveFocus(FocusDirection.Out)
        }
      }
      false
    }
    // .focusTarget(),
) {
  ...
}
复制代码

我在项目中使用的焦点传递方案大致就是这样，目前只能应付一些较为简单的场景，由于有返回焦点给parent的行为，单个组件不适合有两层Focus的传递，需要把多的一层再拆成组件，不过好在Jetpack Compose写一个组件成本很低。

7. 列表滚动

焦点传递方式虽然大致确定了，但是在焦点移动时，列表也是需要跟着滚动的；

通过官方文档，很快就找到了相关代码：

val listState = rememberLazyListState()
val coroutineScope = rememberCoroutineScope()

LazyColumn(state = listState) {
    // ...
}

ScrollToTopButton(
    onClick = {
        coroutineScope.launch {
            // Animate scroll to the first item
            listState.animateScrollToItem(index = 0)
        }
    }
)
复制代码

借助LazyListState就能实现列表的滚动，相关方法大概有：

listState.scrollBy(value)
listState.scrollToItem(index, offset)
listState.animateScrollBy(value, animationSpec)
listState.animateScrollToItem(index, offset)
复制代码

单从使用上看animateScrollToItem()比较符合需要，给上面的Box1添加相关配置，并在focusIndex变化时触发滚动：

val listState = rememberLazyListState()
...

LazyColumn(
  state = listState
  ...
) {
  ...
}

LaunchedEffect(focusIndex) {
  listState.animateScrollToItem(focusIndex)
}
复制代码

可以看到animateScrollToItem()滚动效果不尽人意，所以我们需要自己去算滚动距离并使用animateScrollBy()来滚动；

这方面的实现我基本就抄了SampleComposeApp：

interface ScrollBehaviour {
  suspend fun onScroll(state: LazyListState, focusIndex: Int)
}

object VerticalScrollBehaviour : ScrollBehaviour {
  override suspend fun onScroll(state: LazyListState, focusIndex: Int) {
    val focusItem = state.layoutInfo.visibleItemsInfo.find { focusIndex == it.index } ?: return
      
    val viewStart = state.layoutInfo.viewportStartOffset
    val viewEnd = state.layoutInfo.viewportEndOffset
    val viewSize = viewEnd - viewStart

    val itemStart = focusItem.offset
    val itemEnd = focusItem.offset + focusItem.size
    
    // 这里加点距离主要是为了让下一个目标控件绘制出来，不然在visibleItemsInfo会找不到
    val offSect = 80

    val value = when {
      itemStart < viewStart -> itemStart.toFloat() - offSect
      itemEnd > viewStart + viewSize -> (itemEnd - viewSize - viewStart).toFloat() + offSect
      else -> return
    }
    state.animateScrollBy(value, tween(150, 0, LinearEasing))
  }
}

suspend fun LazyListState.animateScrollToItem(focusIndex: Int, scrollBehaviour: ScrollBehaviour) {
  scrollBehaviour.onScroll(this, focusIndex)
}
复制代码

再把Box1里的滚动代码修改下就完成了：

listState.animateScrollToItem(focusIndex, VerticalScrollBehaviour)
复制代码

8. 播放器

这块我基本都是参照了ComposeVideoPlayer，它的结构设计的非常好，我只把它里面触摸部分换成了按键的；

大致如下，界面方面最外层一个Box，里面个三个控件分别是：

第一层画面MediaPlayerLayout()
第二层按钮、进度条等小组件MediaControlLayout()
第三层监听KeyEventMediaControlKeyEvent()

@Composable
fun TvVideoPlayer(
  player: Player,
  controller: VideoPlayerController,
  modifier: Modifier = Modifier,
) {
  CompositionLocalProvider(
    LocalVideoPlayerController provides controller
  ) {
    Box(modifier = modifier.background(Color.Black)) {
      MediaPlayerLayout(player, modifier = Modifier.matchParentSize())
      MediaControlLayout(modifier = Modifier.matchParentSize())
      MediaControlKeyEvent(modifier = Modifier.matchParentSize())
    }
  }
}

internal val LocalVideoPlayerController =
  compositionLocalOf<VideoPlayerController> { error("VideoPlayerController is not initialized") }
复制代码

使用VideoPlayerController去控制播放和获取当前播放状态：

interface VideoPlayerController {
  val state: StateFlow<VideoPlayerState>
  val isPlaying: Boolean
  fun play()
  fun pause()
  fun playToggle()
  fun reset()
  fun seekTo(positionMs: Long)
  fun seekForward()
  fun seekRewind()
  fun seekFinish()
  fun showControl()
  fun hideControl()
}
复制代码

8.1 MediaPlayerLayout

播放器使用常规的Exoplayer，通过AndroidView去加载它；

@Composable
fun PlayerSurface(
  modifier: Modifier = Modifier,
  onPlayerViewAvailable: (PlayerView) -> Unit = {}
) {
  AndroidView(
    modifier = modifier,
    factory = { context ->
      PlayerView(context).apply {
        useController = false // 关闭默认的控制界面
        onPlayerViewAvailable(this)
      }
    }
  )
}
复制代码

基于VideoPlayerController类，再对PlayerSurface做个封装，在onStart、onStop、onDestory做些常规处理：

@Composable
fun MediaPlayerLayout(player: Player, modifier: Modifier = Modifier) {
  val controller = LocalVideoPlayerController.current
  val state by controller.state.collectAsState()

  val lifecycle = LocalLifecycleOwner.current.lifecycle

  PlayerSurface(modifier) { playerView ->
    playerView.player = player

    lifecycle.addObserver(object : LifecycleObserver {
      @OnLifecycleEvent(Lifecycle.Event.ON_START)
      fun onStart() {
        playerView.keepScreenOn = true
        playerView.onResume()
        if (state.isPlaying) {
          controller.play()
        }
      }

      @OnLifecycleEvent(Lifecycle.Event.ON_STOP)
      fun onStop() {
        playerView.keepScreenOn = false
        playerView.onPause()
        controller.pause()
      }
    })
  }
  
  DisposableEffect(Unit) {
    onDispose {
      player.release()
    }
  }
}
复制代码

8.2 MediaControlLayout

根据当前播放状态，显示播放/暂停按钮、快进/快退按钮、进度条等；

@Composable
fun MediaControlLayout(modifier: Modifier = Modifier) {
  val controller = LocalVideoPlayerController.current
  val state by controller.state.collectAsState()

  val isSeeking by remember(state.seekDirection) {
    mutableStateOf(state.seekDirection.isSeeking)
  }

  if (!state.controlsVisible && !isSeeking) {
    return
  }

  val position = remember(state.currentPosition) { getDurationString(state.currentPosition) }
  val duration = remember(state.duration) { getDurationString(state.duration) }

  Box(modifier = modifier) {

    Column(
      modifier = Modifier
        .fillMaxWidth()
        .align(Alignment.BottomCenter)
        .padding(4.dp)
    ) {
      TimeTextBar(
        modifier = Modifier
          .fillMaxWidth()
          .padding(bottom = 4.dp),
        position = position,
        duration = duration
      )
      SmallSeekBar(
        modifier = Modifier
          .fillMaxWidth(),
        secondaryProgress = state.bufferedPosition,
        progress = state.currentPosition,
        max = state.duration,
      )
    }

    if (!isSeeking) {
      PlayToggleButton(
        modifier = Modifier.align(Alignment.Center),
        isPlaying = state.isPlaying,
        playbackState = state.playbackState
      )
    }
  }
}
复制代码

8.3 MediaControlKeyEvent

定义个空白的Box并监听onKeyEvent，这里就不用考虑传给FocusManager了，直接消费掉按键；

@Composable
fun MediaControlKeyEvent(modifier: Modifier = Modifier) {
  val controller = LocalVideoPlayerController.current
  val state by controller.state.collectAsState()

  val focusRequester = remember { FocusRequester() }

  Box(
    modifier = modifier
      .onFocusDirection {
        when (it) {
          FocusDirection.In -> {
            if (state.isPlaying) {
              controller.pause()
              controller.showControl()
            } else {
              controller.play()
              controller.hideControl()
            }
            true
          }
          FocusDirection.Down -> {
            if (state.controlsVisible) {
              controller.hideControl()
            } else {
              controller.showControl()
            }
            true
          }
          FocusDirection.Left -> {
            controller.seekRewind()
            true
          }
          FocusDirection.Right -> {
            controller.seekForward()
            true
          }
          FocusDirection.Out -> {
            if (state.controlsVisible) {
              controller.hideControl()
              true
            } else false
          }
          else -> false
        }
      }
      .focusRequester(focusRequester)
      .focusTarget(),
  ) {
    VideoSeekAnimation(
      modifier = Modifier.matchParentSize(),
      seekDirection = state.seekDirection,
    )
  }

  SideEffect {
    focusRequester.requestFocus()
  }
}
复制代码

9. Jetpack Compose中使用ViewModel

9.1 一般 ViewModel

// implementation("androidx.lifecycle:lifecycle-viewmodel-compose:2.4.0-beta01")
val viewModel: FeedViewModel = viewModel()
复制代码

9.2 Hilt Inject ViewModel

目前官方好像只提供了基于navigation的实现版本：

# Dagger/Hilt ViewModel Injection (with compose and navigation-compose)

// implementation("androidx.hilt:hilt-navigation-compose:1.0.0-alpha03")
val viewModel: FeedViewModel = hiltViewModel()
复制代码

9.3 Hilt AssistedInject ViewModel

逛Github的时候看到有大佬在Jetpack Compose中使用了这种方式，我觉得还是很不错的，对于函数式的Jetpack Compose来说，在创建ViewModel的时候传入参数是比较合适的；

class DetailViewModel @AssistedInject constructor(
  @Assisted id: Long,
  ...
) : ViewModel() {
  ...

  @dagger.assisted.AssistedFactory
  interface AssistedFactory {
    fun create(id: Long): DetailViewModel
  }
}
复制代码

缺点是用AssistedInject注入要写的代码会多一些，有时候使用像produceState这种方式会更简单，具体就看情况使用；

@Composable
fun DetailScreen(id: Long) {
    val viewState by produceState(initialValue = DetailViewState.Empty) {
      viewModel.loadState(id).collect {
        value = it
      }
    }
    ...
}
复制代码

如何注入可参考：AssistedInject viewModel with Jetpack Compose

参考里面可以做一些下面的调整：

把@IntoMap改成@IntoSet就可以不用配置@AssistedFactoryKey;

AssistedFactoryModule.kt可以使用ksp去生成，我是这么写的AssistedFactoryProcessor，生成的hilt代码大致如下：

@InstallIn(SingletonComponent::class)
@Module
public interface DetailViewModelFactoryModule {
  @Binds
  @IntoMap
  @AssistedFactoryQualifier
  @AssistedFactoryKey(DetailViewModel.AssistedFactory::class)
  public fun bindDetailViewModelFactory(factory: DetailViewModel.AssistedFactory): Any
}
复制代码

还有我跑了下--dry-run好像kapt task有依赖ksp task，这样用ksp生成hilt module在task执行顺序上应该没问题，目前试下来也没遇到什么问题。

./gradlew app:kaptDebugKotlin --dry-run

// ....
// :app:kspDebugKotlin SKIPPED
// :app:kaptGenerateStubsDebugKotlin SKIPPED
// :app:kaptDebugKotlin SKIPPED
复制代码

也可以使用Tlaster大佬在TwidereProject中的方案收集AssistedFactory。

其他

1. 使用Jetpack Compose制作图标

前段时间抄fundroid大佬的俄罗斯方块代码时，发现了一个很有趣的小技巧：

编写一个@Composable fun AppIcon() {...}，通过预览功能右击"copy image"保存图片，就可以简单制作一个App图标；对于像我这样不会ps的来说还是挺有用的。

2. 查看Icons

在使用Icons图标的时候，因为看不到预览挺麻烦的，在官方上找到了这个网站Google Fonts，目前我是在这里搜索和预览的，不知道有没有更好的方式。

3. 屏幕适配

在Jetpack Compose中提供了.dp、.sp扩展，换算则是借助了Density这个类，在Android中这个类是这样创建的：

fun Density(context: Context): Density =
  Density(
    context.resources.displayMetrics.density,
    context.resources.configuration.fontScale
  )
复制代码

可以看出直接使用AndroidAutoSize这类库就能达到效果，但是为了项目能更Compose些，我这里还是自定义了下Density：

fun autoSizeDensity(context: Context, designWidthInDp: Int): Density =
  with(context.resources) {
    val isVertical = configuration.orientation == Configuration.ORIENTATION_PORTRAIT

    val scale = displayMetrics.run {
      val sizeInDp = if (isVertical) widthPixels else heightPixels
      sizeInDp.toFloat() / density / designWidthInDp
    }

    Density(
      density = displayMetrics.density * scale,
      fontScale = configuration.fontScale * scale
    )
  }
  
// 使用
setContent {
  ...
  CompositionLocalProvider(
    LocalDensity provides autoSizeDensity(this@AnimeTvActivity, 480)
  ) {
    ...
  }
}
复制代码

PS: 上面的方法只能适配Compose，不支持AndroidView。

4. 取消点击波纹

Jetpack Compose在点击时默认有波纹的，对TV来说并不需要；

一开始我是参照stackoverflow.com/a/66839858/… 处理的：

@SuppressLint("UnnecessaryComposedModifier")
fun Modifier.clickableNoRipple(onClick: () -> Unit): Modifier = composed {
  clickable(
    indication = null,
    interactionSource = remember { MutableInteractionSource() },
    onClick = onClick
  )
}
复制代码

但是每个点击都这么配置太麻烦了，所以我还是自定义了LocalIndication：

object NoRippleIndication : Indication {
  private object NoIndicationInstance : IndicationInstance {
    override fun ContentDrawScope.drawIndication() {
      drawContent()
    }
  }

  @Composable
  override fun rememberUpdatedInstance(interactionSource: InteractionSource): IndicationInstance {
    return NoIndicationInstance
  }
}

// 使用
setContent {
  ...
  MaterialTheme {
    CompositionLocalProvider(
      LocalIndication provides NoRippleIndication
    ) {
      ...
    }
  }
}
复制代码

注意MaterialTheme会配置LocalIndication，所以要放在MaterialTheme里面去CompositionLocalProvider() {}；

@Composable
fun MaterialTheme(
    ...
) {
    ...
    CompositionLocalProvider(
        LocalColors provides rememberedColors,
        LocalContentAlpha provides ContentAlpha.high,
        LocalIndication provides rippleIndication,
        LocalRippleTheme provides MaterialRippleTheme,
        LocalShapes provides shapes,
        LocalTextSelectionColors provides selectionColors,
        LocalTypography provides typography
    ) {
        ...
    }
}
复制代码

5. 注入小组件

我尝试在界面上加载一些小组件，如fps等；一开始我是放在app里的，后面就想着把它放入其他module里面通过注入的方式去加载它，主要想研究下这方面的可行性；

一开始我想着使用ASM去收集这些小组件的@Composable函数，好在巨佬给了建议，ASM入局太晚，彼时的Compose代码是比较复杂的，要实现并不容易, 对于还没写过ASM的我来说这条路≈不可能，及时止损没有误入歧途（怂了）;

之后我还是用了老方法：使用ksp生成hilt代码来注入Composable组件；

@Retention(AnnotationRetention.SOURCE)
@Target(AnnotationTarget.FUNCTION)
annotation class CollectCompose(
  val qualifier: KClass<out Any>
)

interface CollectComposeOwner<in T> {
  @Composable
  fun Show(scope: T)
}

@Composable
fun <T> T.Show(owners: Collection<CollectComposeOwner<T>>) {
  owners.forEach { owner -> owner.Show(this) }
}
复制代码

我本来是不想写CollectComposeOwner接口的，但是@Composable是kcp处理的，而kapt晚于kcp，所以对hilt来说，@Composable (BoxScope) -> Unit已经通过编译变成Function3<BoxScope, Composer, Int, Unit>，不便于收集了；

ksp收集@CollectCompose 我是这么写的：CollectComposeProcessor，生成的hilt代码大致如下：

@InstallIn(ActivityComponent::class)
@Module
object FpsScreenComponentModule {
  @Provides
  @IntoSet
  @CollectScreenComponentQualifier
  fun provideFpsScreenComponent() = object : CollectComposeOwner<BoxScope> {
    @Composable
    override fun Show(scope: BoxScope) {
      scope.FpsScreenComponent()
    }
  }
}
复制代码

大致使用：

@CollectCompose(CollectScreenComponentQualifier::class)
@Composable
fun BoxScope.FpsScreenComponent() {
  ...
}
复制代码

@AndroidEntryPoint
class AnimeTvActivity : ComponentActivity() {

  @Inject
  @CollectScreenComponentQualifier
  lateinit var collectScreenComponents: Set<@JvmSuppressWildcards CollectComposeOwner<BoxScope>>
    
  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContent {
      Box() {
        AppScreen()
        Show(collectScreenComponents)
      }
    }
  }
}
复制代码

除了在界面显示fps，我也尝试以此实现Compose Toast（只是尝试，不建议这么用）：

object ToastUtils {
  fun showToast(msg: String?) {
    if (msg == null) return
    channel.trySend(msg)
  }
}

private val channel = Channel<String>(1)

@CollectCompose(CollectScreenComponentQualifier::class)
@Composable
fun BoxScope.ToastScreenComponent() {

  var isShown by remember { mutableStateOf(false) }
  var showMsg by remember { mutableStateOf("") }

  LaunchedEffect(Unit) {
    channel.receiveAsFlow().collect {
      showMsg = it
      isShown = true
    }
  }

  AnimatedVisibility(
    visible = isShown,
    modifier = Modifier
      .padding(10.dp)
      .padding(bottom = 50.dp)
      .align(Alignment.BottomCenter),
    enter = fadeIn(),
    exit = fadeOut()
  ) {
    Text(
      text = showMsg,
      modifier = Modifier
        .shadow(1.dp, CircleShape)
        .background(MaterialTheme.colors.surface, CircleShape)
        .padding(horizontal = 20.dp, vertical = 10.dp)
    )
  }

  if (isShown) {
    LaunchedEffect(isShown) {
      delay(1500)
      isShown = false
    }
  }
}
复制代码

右上角加了一个按钮是想试这个radiography，很不错的一个库，输出当前界面的Tree，支持Compose，效果如下：