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社区首页 >问答首页 >无法创建类ViewModel的实例，无法找到原因

问无法创建类ViewModel的实例，无法找到原因
EN

Stack Overflow用户
提问于 2022-08-12 14:07:30
回答 2查看 408关注 0票数 1

每当我点击标题时，应用程序Crashes就会显示我对Android来说是个新手，使用匕首柄，系外玩家，

这就是我碰到错误的地方：

​

​

松片

代码语言：javascript
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@AndroidEntryPoint
class SongFragments : Fragment(R.layout.fragment_song) {

    @Inject
    lateinit var glide: RequestManager

    private lateinit var mainViewModel: MainViewModel

    private val songViewModel: SongViewModel by viewModels()


    private var curplayingSong: sound? = null

    private var playbackState: PlaybackStateCompat? = null

    private var shouldUpdateSeekbar = true

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        mainViewModel = ViewModelProvider(requireActivity()).get(MainViewModel::class.java)
        subscribeToObservers()


        ivPlayPauseDetail.setOnClickListener {
            curplayingSong?.let {
                mainViewModel.playOrToggleSound(it, true)
            }
        }

       seekBar.setOnSeekBarChangeListener(object : SeekBar.OnSeekBarChangeListener {
           override fun onProgressChanged(seekBar: SeekBar?, progress: Int, fromUser: Boolean) {
               if (fromUser) {
                   setCurPlayerTimeToTextView(progress.toLong())
               }
           }

           override fun onStartTrackingTouch(seekBar: SeekBar?) {
              shouldUpdateSeekbar = false

           }

           override fun onStopTrackingTouch(seekBar: SeekBar?) {
              seekBar?.let {
                  mainViewModel.seekTo(it.progress.toLong())
                  shouldUpdateSeekbar = true
              }
           }

       })

        ivSkipPrevious.setOnClickListener {
            mainViewModel.skipToPreviousSound()
        }
        ivSkip.setOnClickListener{
            mainViewModel.skipToNextSound()
        }
    }



    private fun updateTitleAndSongImage(sound: sound) {
        val title = "${sound.title} - ${sound.subtitle}"
        tvSongName.text = title
        glide.load(sound.imageUrl).into(ivSongImage)
    }

    private fun subscribeToObservers() {
        mainViewModel.mediaItems.observe(viewLifecycleOwner){
            it?.let { result ->
                when(result.status){
                    Status.SUCCESS -> {
                       result.data?.let { sounds ->
                           if (curplayingSong == null && sounds.isNotEmpty()) {
                               curplayingSong = sounds[0]
                               updateTitleAndSongImage(sounds[0])
                           }
                       }
                    }
                    else -> Unit
                }
            }
        }
     mainViewModel.curPlayingSound.observe(viewLifecycleOwner) {
         if(it == null) return@observe
         curplayingSong = it.toSong()
         updateTitleAndSongImage(curplayingSong!!)
     }

        mainViewModel.playbackState.observe(viewLifecycleOwner) {
          playbackState = it
            ivPlayPauseDetail.setImageResource(
                if (playbackState?.isPlaying == true) R.drawable.ic_pause else R.drawable.ic_play
            )
            seekBar.progress = it?.position?.toInt() ?: 0
        }

        songViewModel.curPlayerPosition.observe(viewLifecycleOwner) {
           if (shouldUpdateSeekbar) {
               seekBar.progress = it.toInt()
               setCurPlayerTimeToTextView(it)
           }
        }
        songViewModel.curSongDuration.observe(viewLifecycleOwner) {
            seekBar.max = it.toInt()
            val dateFormat = SimpleDateFormat("mm:ss", Locale.getDefault())
            tvSongDuration.text = dateFormat.format(it)
        }

    }

    private fun  setCurPlayerTimeToTextView(ms: Long) {
        val dateFormat = SimpleDateFormat("mm:ss", Locale.getDefault())
        tvCurTime.text = dateFormat.format(ms)
    }


}

SongviewModel

代码语言：javascript
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class SongViewModel @ViewModelInject constructor(
    musicServiceConnection: MusicServiceConnection
) : ViewModel() {

    private val playbackState = musicServiceConnection.playBackState

    private  val _curSongDuration = MutableLiveData<Long>()
    val curSongDuration: LiveData<Long> = _curSongDuration

    private val _curPlayerPosition = MutableLiveData<Long>()
    val curPlayerPosition: LiveData<Long> = _curPlayerPosition

    init {
        updateCurrentplayerPostion()
    }

    @SuppressLint("NullSafeMutableLiveData")
    private fun updateCurrentplayerPostion() {
        viewModelScope.launch {
            while(true) {
             val pos = playbackState.value?.currentPlaybackPosition
                if(curPlayerPosition.value != pos){
                    _curPlayerPosition.postValue(pos)
                    _curSongDuration.postValue(MusicService.curSoundDuration)
                }
                delay(UPDATE_PLAYER_POSITION_INTERVAL)
            }
        }
    }
}

逻辑猫：

代码语言：javascript
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2022-08-12 19:11:39.122 10888-10983/com.fridayhouse.snoozz E/ion: ioctl c0044901 failed with code -1: Invalid argument
2022-08-12 19:11:39.318 10888-10888/com.fridayhouse.snoozz E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.fridayhouse.snoozz, PID: 10888
    java.lang.RuntimeException: Cannot create an instance of class com.fridayhouse.snoozz.ui.viewmodels.SongViewModel
        at androidx.lifecycle.ViewModelProvider$NewInstanceFactory.create(ViewModelProvider.kt:204)
        at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.kt:322)
        at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.kt:304)
        at androidx.lifecycle.SavedStateViewModelFactory.create(SavedStateViewModelFactory.kt:175)
        at androidx.lifecycle.SavedStateViewModelFactory.create(SavedStateViewModelFactory.kt:203)
        at dagger.hilt.android.internal.lifecycle.HiltViewModelFactory.create(HiltViewModelFactory.java:111)
        at androidx.lifecycle.ViewModelProvider$Factory.create(ViewModelProvider.kt:83)
        at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.kt:187)
        at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.kt:153)
        at androidx.lifecycle.ViewModelLazy.getValue(ViewModelLazy.kt:53)
        at androidx.lifecycle.ViewModelLazy.getValue(ViewModelLazy.kt:35)
        at com.fridayhouse.snoozz.ui.fragments.SongFragments.getSongViewModel(SongFragments.kt:33)
        at com.fridayhouse.snoozz.ui.fragments.SongFragments.subscribeToObservers(SongFragments.kt:121)
        at com.fridayhouse.snoozz.ui.fragments.SongFragments.onViewCreated(SongFragments.kt:45)
        at androidx.fragment.app.Fragment.performViewCreated(Fragment.java:3128)
        at androidx.fragment.app.FragmentStateManager.createView(FragmentStateManager.java:552)
        at androidx.fragment.app.FragmentStateManager.moveToExpectedState(FragmentStateManager.java:261)
        at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:1890)
        at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:1814)
        at androidx.fragment.app.FragmentManager.execPendingActions(FragmentManager.java:1751)
        at androidx.fragment.app.FragmentManager$5.run(FragmentManager.java:538)
        at android.os.Handler.handleCallback(Handler.java:938)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loopOnce(Looper.java:233)
        at android.os.Looper.loop(Looper.java:334)
        at android.app.ActivityThread.main(ActivityThread.java:8396)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:582)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1068)
     Caused by: java.lang.InstantiationException: java.lang.Class<com.fridayhouse.snoozz.ui.viewmodels.SongViewModel> has no zero argument constructor
        at java.lang.Class.newInstance(Native Method)
        at androidx.lifecycle.ViewModelProvider$NewInstanceFactory.create(ViewModelProvider.kt:202)
        at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.kt:322) 
        at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.kt:304) 
        at androidx.lifecycle.SavedStateViewModelFactory.create(SavedStateViewModelFactory.kt:175) 
        at androidx.lifecycle.SavedStateViewModelFactory.create(SavedStateViewModelFactory.kt:203) 
        at dagger.hilt.android.internal.lifecycle.HiltViewModelFactory.create(HiltViewModelFactory.java:111) 
        at androidx.lifecycle.ViewModelProvider$Factory.create(ViewModelProvider.kt:83) 
        at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.kt:187) 
        at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.kt:153) 
        at androidx.lifecycle.ViewModelLazy.getValue(ViewModelLazy.kt:53) 
        at androidx.lifecycle.ViewModelLazy.getValue(ViewModelLazy.kt:35) 
        at com.fridayhouse.snoozz.ui.fragments.SongFragments.getSongViewModel(SongFragments.kt:33) 
        at com.fridayhouse.snoozz.ui.fragments.SongFragments.subscribeToObservers(SongFragments.kt:121) 
        at com.fridayhouse.snoozz.ui.fragments.SongFragments.onViewCreated(SongFragments.kt:45) 
        at androidx.fragment.app.Fragment.performViewCreated(Fragment.java:3128) 
        at androidx.fragment.app.FragmentStateManager.createView(FragmentStateManager.java:552) 
        at androidx.fragment.app.FragmentStateManager.moveToExpectedState(FragmentStateManager.java:261) 
        at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:1890) 
        at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:1814) 
        at androidx.fragment.app.FragmentManager.execPendingActions(FragmentManager.java:1751) 
        at androidx.fragment.app.FragmentManager$5.run(FragmentManager.java:538) 
        at android.os.Handler.handleCallback(Handler.java:938) 
        at android.os.Handler.dispatchMessage(Handler.java:99) 
        at android.os.Looper.loopOnce(Looper.java:233) 
        at android.os.Looper.loop(Looper.java:334) 
        at android.app.ActivityThread.main(ActivityThread.java:8396) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:582) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1068) 
dagger-hilt
android
kotlin
mvvm
android-viewmodel
EN

回答 2

Stack Overflow用户

回答已采纳

发布于 2022-08-16 08:08:35

@ViewModelInject已被废弃。您可以通过检查这里获取更多信息。

在较新的版本中，需要用@AndroidViewModel注释viewmodel类，用@Inject对构造函数进行注释。

代码语言：javascript
运行
复制
@AndroidViewModel
class SongViewModel @Inject constructor(
    musicServiceConnection: MusicServiceConnection
) : ViewModel()

希望它能解决这个问题。

票数 0
EN

Stack Overflow用户

发布于 2022-08-12 14:48:27

既然您使用的是Hilt，就不应该使用by viewModels()。您应该在提供程序中设置您的MusicServiceConnection，而不是使用private val songViewModel: SongViewModel by viewModels()，而是使用@Inject private lateinit var songViewModel: SongViewModel。

我对希尔特不太熟悉，所以我不能提供更多的指导。下面是对by viewModels()出了什么问题的解释，以及如果不是使用依赖注入框架的，您将如何解决这个问题。

在活动或片段中创建ViewModel时，可以提供负责创建ViewModel实例的工厂。如果不提供工厂，则使用默认工厂。

只有当您的ViewModel构造函数的参数为下列之一时，默认工厂才能创建ViewModel实例：

  • constructor()空构造函数(没有参数)
  • constructor(savedStateHandle: SavedStateHandle)
  • constructor(application: Application)
  • constructor(application: Application, savedStateHandle: SavedStateHandle)

我不认为这是很好的记录。我必须看一下Jetpack源代码才能了解它。

由于ViewModel需要一个MusicServiceConnection参数，所以不能使用默认工厂。您需要将显式ViewModelProvider.Factory作为参数提供给by viewModels()。

这场训练有一个为ViewModel创建一个需要构造函数特殊参数的ViewModelProvider.Factory类的示例。在您的例子中，解决方案可能如下所示：

代码语言：javascript
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复制
class SongViewModelFactory(private val musicServiceConnection: MusicServiceConnection) : ViewModelProvider.Factory {
    override fun <T : ViewModel> create(modelClass: Class<T>): T {
        require(modelClass.isAssignableFrom(SongViewModel::class.java)) { "Unknown ViewModel class" }
        @Suppress("UNCHECKED_CAST")
        return SongViewModel(musicServiceConnection) as T
    }
}

我不知道您的MusicServiceConnection类是从哪里来的，但是让我们假设您可以简单地为您的活动实例化它一次，使用一个空的构造函数。然后你就会替换

代码语言：javascript
运行
复制
private val songViewModel: SongViewModel by viewModels()

使用

代码语言：javascript
运行
复制
private val songViewModel: SongViewModel by viewModels {
    SongViewModelFactory(MusicServiceConnection())
}

注意，您将一个lambda函数传递给viewModels，而不是直接传递工厂的一个实例。这是因为工厂只创建了一次，即使您的活动被多次重新创建(比如用户来回旋转屏幕)。这个lambda中的代码仅在应用程序导航到此屏幕时调用一次，即使该活动是为屏幕旋转或其他配置更改重新创建的。

票数 0
EN
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：

https://stackoverflow.com/questions/73335428

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