想在使用Latlon的Livedata时添加textView的延迟

Question

使用MutableLiveData将服务之间的数据传递给片段。 根据日志。 但是，当我尝试使用TextView显示数据时，我会毫无用处。它认为延迟使其无效。有没有办法延迟或更新文本视图，以便我可以显示数据？

dashbordfragment.kt

class DashbordFragment : Fragment() {

private var locationList = mutableListOf<LatLng>()
var liveLatLng = MutableLiveData<LatLng>()

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setHasOptionsMenu(true)
    sendActionCommandToService(Constants.ACTION_SERVICE_START)
}

override fun onCreateView(
    inflater: LayoutInflater, container: ViewGroup?,
    savedInstanceState: Bundle?
): View? {
    observerTrackerService()
    // Inflate the layout for this fragment
    return inflater.inflate(R.layout.fragment_dashbord, container, false)
}
lateinit var binding : FragmentDashbordBinding
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    super.onViewCreated(view, savedInstanceState)

    binding = FragmentDashbordBinding.bind(view)

    binding.btGotostation.setOnClickListener {

        startActivity(Intent(requireContext(),StationsActivity::class.java))
    }
    binding.btGotostatistics.setOnClickListener {
        findNavController().navigate(DashbordFragmentDirections.actionDashbordFragmentToStatisticsFragment())
    }

    binding.btGotolinediagram.setOnClickListener {
        findNavController().navigate(DashbordFragmentDirections.actionDashbordFragmentToLineDiagramFragment())
    }

    binding.btMap.setOnClickListener {
        findNavController().navigate(DashbordFragmentDirections.actionDashbordFragmentToMapsFragment())
    }
    binding.latlon.text = liveLatLng.value.toString()


}

override fun onCreateOptionsMenu(menu: Menu, inflater: MenuInflater) {
    inflater.inflate(R.menu.dashboard_menu, menu)
    super.onCreateOptionsMenu(menu, inflater)
}

override fun onOptionsItemSelected(item: MenuItem): Boolean {

    return super.onOptionsItemSelected(item)
}

private fun observerTrackerService(){
    TrackerService.locationList.observe(viewLifecycleOwner) {

        if (it != null) {
            locationList = it
            Log.d("LocationList",locationList.toString())
        }
    }
    TrackerService.liveLatLng.observe(viewLifecycleOwner){

        Log.d("LiveLatLng", it.toString())
    }
    Log.d("LocationList", "Tester")

}
private fun sendActionCommandToService(action: String){
    Intent(
        requireContext(),
        TrackerService::class.java
    ).apply {
        this.action = action
        requireContext().startService(this)
    }
}

---

fragment_dashbord.xml

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    >


    <TextView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_gravity="top|center"
        android:text="@string/dashboard"
        android:textAlignment="center"
        android:textAppearance="@style/TextAppearance.AppCompat.Large" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/go_to_station"
        android:layout_marginStart="24dp"
        android:layout_marginTop="54dp"
        android:id="@+id/bt_gotostation"/>

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/GoogleMap"
        android:layout_marginStart="24dp"
        android:layout_marginTop="140dp"
        android:id="@+id/btMap"/>

    <TextView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:text="@string/statistics_desc"
        android:layout_marginTop="240dp"
        android:textAlignment="center"
        android:textAppearance="@style/TextAppearance.AppCompat.Medium" />


    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/development_bar_chart"
        android:layout_marginStart="24dp"
        android:layout_marginTop="290dp"
        android:id="@+id/bt_gotostatistics"/>

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/development_line_diagram"
        android:layout_marginStart="24dp"
        android:layout_marginTop="360dp"
        android:id="@+id/bt_gotolinediagram"/>

    <TextView
        android:id="@+id/latlon"
        android:layout_width="100dp"
        android:layout_height="100dp"
        android:text="@string/statistics_desc"
        android:layout_marginTop="500dp"
        android:textAlignment="center"
        android:textAppearance="@style/TextAppearance.AppCompat.Medium" />

</FrameLayout>

Answer 1

您正在用onviewCreated进行设置，该比收到数据之前称为。
相反，您可以在onviewCreated中设置一个观察者。
示例：

liveLatLng.observe(this , Observer {
    it?.let{
        binding.latlon.text = it.toString()
    }
})

并设置值如下

TrackerService.liveLatLng.observe(viewLifecycleOwner){
    liveLatLng.value = it // hoping this is of type LatLng
}

注意：根据Android Dev Docs考虑

确保存储更新UI的Livedata对象
与活动或碎片相对的对象，以下
原因：避免活动和碎片。现在这些UI
控制器负责显示数据，但不持有数据
状态。将寿命的实例与特定活动或
片段实例，允许生命的对象生存在配置中
更改。

来自开发人员文档

Answer 2

此binding.latlon.text = livelatlng.value.tostring（）与livedata没有任何共同点。正确使用时，您的代码应该看起来像binding.latlon = livelatlng，并且无需延迟，livedata将为您做。要达到这一点，您需要的只是检查 livedata> livedata ， databinding and bindingAdapter 。

小提示，用于所需的绑定变量

<import type="com.google.type.LatLng" />

<variable
    name="latlon"
    type="androidx.lifecycle.MutableLiveData<LatLng>" />