Android-LiveData随机不触发更新值（深度问题）

Question

活动不是问题的一部分。它只是初始化导航图和它的生命周期方法在pause，ondestroy...你可以从视频中推断出（显然，onCreate和onResume被称为点击“smistamento A giro”的瞬间）

在本演示中使用了两个片段，SmistamentoGiroTabFragment（它将子片段作为选项卡，但对于本问题的目的并不重要）和SmistaMentogiroCercagiroFragment。要从一个切换到一个,需要使用两个操作：

• FindNavController（）。导航（SmistaMentogirotabFragmentDirections.ActionDashBoardToCercagiro...
• FindNavController（）。导航（SmistaMentoGiroCartellaCarrelloFragmentDirections.ActionGiroToDashboard...

所以每次我从一个切换到一个时,整个生命周期方法都被调用：

// Removed old fragment I am leaving
SmistamentoGiroCercaGiroFragment - onPause
SmistamentoGiroCercaGiroFragment - onDestroy
// New fragment just added
SmistamentoGiroTabFragment - onAttach
SmistamentoGiroTabFragment - onCreate
SmistamentoGiroTabFragment - onViewCreated
SmistamentoGiroTabFragment - onResume

而另一种方式。

Smistamentogirotabfragment

smistamentoGiroTabViewModel.searchLVCount.observe(viewLifecycleOwner, Observer {
    Logger.debug("TestGrafico", "searchLVCount $it")
})

<TextView
android:id="@+id/oggetti"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textStyle="bold"
app:bindInt="@{viewModel.searchLVCount}"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
tools:text="18" />

val searchLVCount = smistamentoGiroRepository.searchLVCount()

@Query("SELECT COUNT(codiceLdV) FROM SmistamentoGiroLV")
fun searchLVCount(): LiveData<Int>

smistamentoGiroTabViewModel.handleArgs(args, activity().currentView)

return smistamentoGiroLVDao.insert(smistamentoGiroLVEntity)

，在片段观察到的表中插入一条记录：

@Insert(onConflict = OnConflictStrategy.REPLACE)
Long insert(SmistamentoGiroLVEntity element);

您在视频中所观看的测试的对应日志如下：“tabwm init”是SmistamentogirotabviewModel中的以下日志：

init {
        Logger.debug("TestGrafico", "TabWM init")
    }

日志：

// First callback when opening the activity
TestGrafico - TabWM init
TestGrafico - 
TestGrafico - searchLVCount 1

// First automatic insertion
TestGrafico - TabWM init
TestGrafico - 
TestGrafico - searchLVCount 1
TestGrafico - searchLVCount 2

// Second automatic insertion
TestGrafico - TabWM init
TestGrafico - 
TestGrafico - searchLVCount 2
TestGrafico - searchLVCount 3

// Third automatic insertion
TestGrafico - TabWM init
TestGrafico - 
TestGrafico - searchLVCount 3
TestGrafico - searchLVCount 4

// Fourth automatic insertion
TestGrafico - TabWM init
TestGrafico - 
TestGrafico - searchLVCount 4

TestGrafico - searchLVCount 5

override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
): View {
    var currentFragment: Fragment? = null
    val binding = FragmentSmistamentoGiroMainBinding.inflate(
            inflater, container, false
    ).apply {
        lifecycleOwner = viewLifecycleOwner

@Inject
lateinit var viewModelFactory: ViewModelProvider.Factory

private val smistamentoGiroTabViewModel: SmistamentoGiroTabViewModel by viewModels {
    viewModelFactory
}

@Binds
abstract fun bindViewModelFactory(factory: MagazzinoViewModelFactory): ViewModelProvider.Factory

@Binds
@IntoMap
@ViewModelKey(SmistamentoGiroTabViewModel::class)
abstract fun bindSmistamentoGiroTabViewModel(smistamentoGiroTabViewModel: SmistamentoGiroTabViewModel): ViewModel

@MustBeDocumented
@Target(
        AnnotationTarget.FUNCTION,
        AnnotationTarget.PROPERTY_GETTER,
        AnnotationTarget.PROPERTY_SETTER
)
@Retention(AnnotationRetention.RUNTIME)
@MapKey
annotation class ViewModelKey(val value: KClass<out ViewModel>)

@Singleton
class MagazzinoViewModelFactory @Inject constructor(
        private val creators: Map<Class<out ViewModel>, @JvmSuppressWildcards Provider<ViewModel>>
) : ViewModelProvider.Factory {
    override fun <T : ViewModel> create(modelClass: Class<T>): T {
        val creator = creators[modelClass] ?: creators.entries.firstOrNull {
            modelClass.isAssignableFrom(it.key)
        }?.value ?: throw IllegalArgumentException("unknown model class $modelClass")
        @Suppress("UNCHECKED_CAST")
        return creator.get() as T
    }
}

TestGrafico - TabWM init SmistamentoGiroTabViewModel@467a7a4
TestGrafico - searchLVCount 18
TestGrafico - searchLVCount 19

TestGrafico - TabWM init SmistamentoGiroTabViewModel@3585336
TestGrafico - searchLVCount 19
TestGrafico - searchLVCount 20

TestGrafico - TabWM init SmistamentoGiroTabViewModel@3351174
TestGrafico - searchLVCount 20
TestGrafico - searchLVCount 21

TestGrafico - TabWM init SmistamentoGiroTabViewModel@c6c785f
// Bug occoured
TestGrafico - searchLVCount 21

由Observer触发的两个值是正确的，因为旧值是fragment/vm初始化，新值是在onCreateView末尾调用的handleArgs方法的结果（导致在db中插入记录），如上面深入解释的。

Answer 1

经过整整一个月的测试和分析项目的架构元素，我找到了解决方案。在初始化Room数据库时，我使用了RoomDatabase.JournalMode.Truncate。

下面是模式的ref链接：https://developer.android.com/reference/android/arch/persistence/room/roomdatabase.journalmode

必须使用的是WRITE_AHEAD_LOGGING（默认使用）。通过使用它，每一个随机图形错误都消失了。