【Android进阶】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()
    )
}

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。

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()

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)
    ...

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
}

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
}

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()
  )
  ...
}

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)

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
}

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)

}
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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
}

}
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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：

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；

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；

可以通过focusManager.moveFocus(FocusDirection.Out)把当前焦点传给parent。

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。

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)
    }
}

)
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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)
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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)
}
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再把Box1里的滚动代码修改下就完成了：
listState.animateScrollToItem(focusIndex, VerticalScrollBehaviour)
复制代码

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 { 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
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()
}
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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)
  }
}

)
}
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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()
}

}
}
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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
  )
}

}
}
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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()

}
}
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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()
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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()
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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
}
}
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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
```
}
}
...
}
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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
}
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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
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也可以使用Tlaster大佬在TwidereProject中的方案收集AssistedFactory。
其他

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。

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。
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
)
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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)

) {

...

}
}
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PS: 上面的方法只能适配Compose，不支持AndroidView。

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
)
}
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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
) {
  ...
}

}
}
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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
) {
    ...
}

}
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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
)

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

@Composable
fun T.Show(owners: Collection>) {
owners.forEach { owner -> owner.Show(this) }
}
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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，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 {

@Composable
override fun Show(scope: BoxScope) {
  scope.FpsScreenComponent()
}

}
}
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大致使用：
@CollectCompose(CollectScreenComponentQualifier::class)
@Composable
fun BoxScope.FpsScreenComponent() {
...
}
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@AndroidEntryPoint
class AnimeTvActivity : ComponentActivity() {

@Inject
@CollectScreenComponentQualifier
lateinit var collectScreenComponents: Set<@JvmSuppressWildcards CollectComposeOwner>

override fun onCreate(savedInstanceState: Bundle?) {

super.onCreate(savedInstanceState)
setContent {
  Box() {
    AppScreen()
    Show(collectScreenComponents)
  }
}

}
}
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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(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
}

}
}
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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：

参考
文章

Jetpack Compose 博物馆
Jetpack Compose 在Twidere X中的实践总结 @Tlaster
Jetpack Compose 中显示富文本 @Tlaster
Jetpack Compose Side Effect：如何处理副作用 @fundroid
Focus in Jetpack Compose @Jamie Sanson
android-rethinking-package-structure @Joe Birch
Hilt 实战 | 创建应用级别 CoroutineScope

项目

TwidereX-Android @Tlaster
Dota-Info @Mitch Tabian
SampleComposeApp @Akila
ComposeVideoPlayer @Halil Ozercan
dpad-compose @Walter Berggren

原文：Seiko