我是Android MVVM的新手，可以说我有2个屏幕要显示，片段A和片段B。
当用户单击“片段A”中的按钮时，然后我检查服务器是否该用户已创建事件，他是否尚未创建事件，然后移至片段B。这是我的“片段A”
class FragmentA : Fragment() {
lateinit var model: AViewModel
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
model = ViewModelProvider(this).get(AViewModel::class.java)
button.setOnClickListener {
model.checkIfUserHasCreatedEvent()
}
model.hasCreatedEvent.observe(this, Observer { hasCreatedEvent ->
if (!hasCreatedEvent) {
val chooseEventNameDestination = CreateEventFragmentDirections.actionToCreateEventName()
findNavController().navigate(chooseEventNameDestination)
}
})
}
}
和这里的fragmentA的视图模型
class AViewModel(application: Application) : AndroidViewModel(application) {
val hasCreatedEvent = UserRepository.hasCreatedEvent
fun checkIfUserHasCreatedEvent() {
UserRepository.checkIfUserHasReachedMaxEventCreationForToday()
}
}
如果用户尚未创建事件(hasCreatedEvent == false)，那么他将从片段A转到片段B。但是问题是，当我想再次从片段B返回片段A
hasCreatedEvent的观察者似乎自动给了false值
model.hasCreatedEvent.observe(this, Observer { hasCreatedEvent ->
// hasCreatedEvent will always be false when I back from fragment B to fragment A
if (!hasCreatedEvent) {
// thats why the block here will be triggered immediately
// and I will move back to fragmentB again
// I want to stay at FragmentA, after back from FragmentB
val chooseEventNameDestination = CreateEventFragmentDirections.actionToCreateEventName()
findNavController().navigate(chooseEventNameDestination)
}
})
我希望当我从fragmentB回到fragmentA时，hasCreatedEvent将为空。我该怎么办 ？这是正确的行为吗？
kotlin或java都可以