Android LiveData在没有观察者的情况下更新数据

我正在编写一个培训预算应用程序，它使用LiveData、数据绑定、Room、MVVM和CLEAN

现在我面临着一个奇怪的问题。当前（应用程序全新启动）我的应用程序看起来像一个带有浮动操作按钮的空屏幕

单击浮动操作按钮将创建新的MonthBalanceDatabase数据类，但前提是数据库中已经并没有当前月份

@Entity(tableName = "month_balance_overview")

data class MonthBalanceDatabase(

@PrimaryKey(autoGenerate = true)

var id: Int = 0,

var year: String, //ex 2020

var month: String, //ex SEPTEMBER

var income: Long = 0,

var consumption: Long = 0,

var balance: Long = 0

)

刀

这就是问题所在。im使用getCurrentMonth方法进行进一步检查。应用程序是否应该创建新的月份

//this is part of my viewModel



private val _currentMonth: LiveData = budgetRepository.currentMonth

val currentMonth: LiveData

    get() = _currentMonth



/**

 * Method called via dataBinding on floating button click

 */

fun addNewMonthIfPossible() {

    if (currentMonth.value == null) {

        scope.launch(Dispatchers.IO) {

            //creating current month with year == 2020 and month == SEPTEMBER

            //and its working good

            budgetRepository.createCurrentMonth(getCurrentYear(), getCurrentMonth())

        }

    }

}

但是，如果我的片段中没有观察者，那么currentMonth将永远不会更新，这将导致我的视图中出现多个类似的月份

因此，当currentMonth上的观察者被注释包围时，我的LiveData将永远不会更新，并且同一个月的多个实例将在浮动按钮单击时添加到DB中。为什么它是这样工作的？有没有一种不用设置观察者的方法来处理它？或者我做错了什么

//this is part of my viewModel



private val _currentMonth: LiveData = budgetRepository.currentMonth

val currentMonth: LiveData

    get() = _currentMonth



/**

 * Method called via dataBinding on floating button click

 */

fun addNewMonthIfPossible() {

    if (currentMonth.value == null) {

        scope.launch(Dispatchers.IO) {

            //creating current month with year == 2020 and month == SEPTEMBER

            //and its working good

            budgetRepository.createCurrentMonth(getCurrentYear(), getCurrentMonth())

        }

    }

}

class MonthOverviewFragment : Fragment() {



lateinit var viewModel: MonthViewModel

lateinit var viewModelFactory: MonthViewModelFactory



override fun onCreateView(

    inflater: LayoutInflater,

    container: ViewGroup?,

    savedInstanceState: Bundle?

): View? {

    val binding: MonthOverviewFragmentBinding = DataBindingUtil.inflate(

        inflater,

        R.layout.month_overview_fragment, container, false

    )



    val application = requireNotNull(this.activity).application



    val dataSource = BudgetDatabase.getInstance(application)



    viewModelFactory = MonthViewModelFactory(dataSource, application)



    viewModel = ViewModelProvider(this, viewModelFactory).get(MonthViewModel::class.java)



    binding.monthViewModel = viewModel

    binding.lifecycleOwner = viewLifecycleOwner



    val adapter = MonthsAdapter()

    binding.monthList.adapter = adapter



    viewModel.existingMonths.observe(viewLifecycleOwner, Observer {

        it?.let {

            adapter.submitList(it)

        }

    })





    //ive noticed that if this line is commented my LiveData will never update

    // but i don't need to observe this variable



    //viewModel.currentMonth.observe(viewLifecycleOwner, Observer {})



    return binding.root

}

}