RecyclerView观察者，片段未更新数据

Question

My MainFragment包含一个教育路径的RecyclerView，当选择一个项目时，它会将用户带到CourseFragment，其中包含相关课程的不同RecyclerView。但是，如果用户返回到第一个RecyclerView并选择不同的路径，则会再次显示相同的数据项。

课程片段

class CourseFragment : Fragment(),
CourseRecyclerAdapter.CourseItemListener {
private lateinit var viewModel: CourseViewModel
private lateinit var recyclerView: RecyclerView
private lateinit var navController: NavController
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
Log.i(LOG_TAG, "Course Fragment onCreateView(): selectedItem = $globalSelectedPath")
val view = inflater.inflate(R.layout.fragment_course, container, false)
recyclerView = view.findViewById(R.id.courseRecyclerView)
navController = Navigation.findNavController(requireActivity(), R.id.nav_host )
viewModel = ViewModelProvider(requireActivity()).get(CourseViewModel::class.java)
viewModel.courseData.observe(viewLifecycleOwner, Observer {
val adapter =
CourseRecyclerAdapter(
requireContext(),
it,
this
)
recyclerView.adapter = adapter
} )
return view
}

CourseViewModel

class CourseViewModel(app: Application): AndroidViewModel(app) {
private val courseDataRepository = CourseRepository(app)
val courseData = courseDataRepository.courseData
val selectedCourse = MutableLiveData<Course>()
}

课程库

class CourseRepository(val app: Application) {
val courseData = MutableLiveData<List<Course>>()
init {
CoroutineScope(Dispatchers.IO).launch {
callWebService()
}
}
@WorkerThread
suspend fun callWebService() {
if (Utility.networkAvailable(app)) {
val retrofit = Retrofit.Builder().baseUrl(WEB_SERVICE_URL).addConverterFactory(MoshiConverterFactory.create()).build()
val service = retrofit.create(CourseService::class.java)
val serviceData = service.getCourseData(globalSelectedPath).body() ?: emptyList()
courseData.postValue(serviceData)
}
else
Toast.makeText(app, Resources.getSystem().getString(R.string.noConnectivity), Toast.LENGTH_LONG).show()
}
}

我添加了一些日志，注意到我的Repository只在应用程序第一次打开时被调用，但再也不会获取数据，因为callWebService((再也不会被调用。

12:24:02.520 I/mylog: Course Fragment onCreateView(): selected path = MOB001
12:24:02.529 I/mylog: Course Repository callWebService(): selected path = MOB001
-------------------------------
12:24:35.009 I/mylog: Course Fragment onCreateView(): selected path = WEB999

我添加了一些http日志来跟踪数据，并确认数据只被检索了一次：

12:24:02.551 D/OkHttp: --> GET https://.../mobile/feed/course_data.php?pathName=MOB001
12:24:02.551 D/OkHttp: --> END GET
12:24:03.007 D/OkHttp: <-- 200 https://.../mobile/feed/course_data.php?pathName=MOB001 (455ms)
12:24:03.007 D/OkHttp: date: Sat, 02 May 2020 09:24:03 GMT
12:24:03.007 D/OkHttp: server: Apache
12:24:03.007 D/OkHttp: x-powered-by: PHP/5.6.40
12:24:03.007 D/OkHttp: vary: Accept-Encoding
12:24:03.007 D/OkHttp: content-type: text/html; charset=UTF-8
12:24:03.009 D/OkHttp: [{"courseName":"Android App Development Essentials","instructor":"John Lennon","courseDescription":"Description ...","courseImage":"android_development_essentials.jpg","instructorImage":"john.jpg"}]
12:24:03.009 D/OkHttp: <-- END HTTP (206-byte body)

Answer 1

您使用的是ViewModelProvider(requireActivity()).get(CourseViewModel::class.java)，这意味着您正在创建作用域为整个活动的CourseViewModel。这意味着在活动的整个生命周期中只会创建一个CourseViewModel实例。

如果您希望每个片段都有一个单独的CourseViewModel(因此，也就是一个独立的CourseRepository实例(，则应该使用ViewModelProvider(this)将ViewModel的范围限定为片段本身：

viewModel = ViewModelProvider(this).get(CourseViewModel::class.java)