Android Can';t在片段中观察ViewModel中的LiveData
在我的Android Can';t在片段中观察ViewModel中的LiveData,android,android-livedata,android-viewmodel,mutablelivedata,Android,Android Livedata,Android Viewmodel,Mutablelivedata,在我的ViewPager的片段之一中有一个RecyclerView。此RecyclerView显示从服务器获取的数据。它正常工作,但我无法使用ViewModel和LiveData实现相同的功能,因为LiveData.observe方法在从ViewModel更改LiveData时没有被调用 下面是我的MonthlyOrderViewModel.java类的源代码 public class MonthlyOrderViewModel extends AndroidViewModel { priva
ViewPager
的片段之一中有一个RecyclerView
。此RecyclerView
显示从服务器获取的数据。它正常工作,但我无法使用ViewModel
和LiveData
实现相同的功能,因为LiveData.observe
方法在从ViewModel
更改LiveData
时没有被调用
下面是我的MonthlyOrderViewModel.java类的源代码
public class MonthlyOrderViewModel extends AndroidViewModel {
private Retrofit retrofit;
private RetrofitServices retrofitServices;
private MutableLiveData<MonthlyOrderHistory> monthlyOrderHistoryMutableLiveData = new MutableLiveData<>();
public MonthlyOrderViewModel(@NonNull Application application) {
super(application);
retrofit = RetrofitFactory.getRetrofit();
retrofitServices = retrofit.create(RetrofitServices.class);
}
public MutableLiveData<MonthlyOrderHistory> getMonthlyOrderHistoryMutableLiveData() {
return monthlyOrderHistoryMutableLiveData;
}
public void fetchMonthlyOrders() {
Call<MonthlyOrderHistory> call = retrofitServices.getAllMonthlyOrderHistory(IpharmaApplication.getInstance().getLoggedInUser().getId());
call.enqueue(new Callback<MonthlyOrderHistory>() {
@Override
public void onResponse(Call<MonthlyOrderHistory> call, Response<MonthlyOrderHistory> response) {
MonthlyOrderHistory monthlyOrderHistory = response.body();
if(monthlyOrderHistory.getStatus().equalsIgnoreCase("success")) {
List<UserOrder> userOrders = monthlyOrderHistory.getOrders().getUserOrder();
if(userOrders != null && userOrders.size() != 0) {
DefaultScheduler.INSTANCE.execute(() -> {
monthlyOrderHistoryMutableLiveData.postValue(monthlyOrderHistory);
return Unit.INSTANCE;
});
}
}
}
@Override
public void onFailure(Call<MonthlyOrderHistory> call, Throwable t) {
t.printStackTrace();
}
});
}
}
interface Scheduler {
fun execute(task: () -> Unit)
fun postToMainThread(task: () -> Unit)
fun postDelayedToMainThread(delay: Long, task: () -> Unit)
}
//A shim [Scheduler] that by default handles operations in the [AsyncScheduler].
object DefaultScheduler : Scheduler {
private var delegate: Scheduler = AsyncScheduler
//Sets the new delegate scheduler, null to revert to the default async one.
fun setDelegate(newDelegate: Scheduler?) {
delegate = newDelegate ?: AsyncScheduler
}
override fun execute(task: () -> Unit) {
delegate.execute(task)
}
override fun postToMainThread(task: () -> Unit) {
delegate.postToMainThread(task)
}
override fun postDelayedToMainThread(delay: Long, task: () -> Unit) {
delegate.postDelayedToMainThread(delay, task)
}
}
//Runs tasks in a [ExecutorService] with a fixed thread of pools
internal object AsyncScheduler : Scheduler {
private val executorService: ExecutorService = Executors.newFixedThreadPool(NUMBER_OF_THREADS)
override fun execute(task: () -> Unit) {
executorService.execute(task)
}
override fun postToMainThread(task: () -> Unit) {
if (isMainThread()) {
task()
} else {
val mainThreadHandler = Handler(Looper.getMainLooper())
mainThreadHandler.post(task)
}
}
private fun isMainThread(): Boolean {
return Looper.getMainLooper().thread === Thread.currentThread()
}
override fun postDelayedToMainThread(delay: Long, task: () -> Unit) {
val mainThreadHandler = Handler(Looper.getMainLooper())
mainThreadHandler.postDelayed(task, delay)
}
}
//Runs tasks synchronously.
object SyncScheduler : Scheduler {
private val postDelayedTasks = mutableListOf<() -> Unit>()
override fun execute(task: () -> Unit) {
task()
}
override fun postToMainThread(task: () -> Unit) {
task()
}
override fun postDelayedToMainThread(delay: Long, task: () -> Unit) {
postDelayedTasks.add(task)
}
fun runAllScheduledPostDelayedTasks() {
val tasks = postDelayedTasks.toList()
clearScheduledPostdelayedTasks()
for (task in tasks) {
task()
}
}
fun clearScheduledPostdelayedTasks() {
postDelayedTasks.clear()
}
}
最后,我尝试使用以下方法观察片段的onCreateView
方法的变化:
MonthlyOrderViewModel monthlyOrderViewModel = new MonthlyOrderViewModel(getActivity().getApplication());
monthlyOrderViewModel.getMonthlyOrderHistoryMutableLiveData().observe(this, monthlyOrderHistory -> {
monthlyOrderRecyclerView = view.findViewById(R.id.monthlyOrderRecyclerView);
monthlyOrderRecyclerViewAdapter = new OrderHistoryRecyclerViewAdapter(getContext(), monthlyOrderHistory.getOrders().getUserOrder());
monthlyOrderRecyclerViewAdapter.notifyDataSetChanged();
monthlyOrderRecyclerView.setAdapter(monthlyOrderRecyclerViewAdapter);
monthlyOrderRecyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
});
我试着对它进行调试,发现改装后获取数据没有问题。但是,当我试图在片段中使用observe
方法时,它永远不会被调用
请告诉我如何解决这个问题?任何帮助都将不胜感激。您不应该使用new
实例化您的ViewModel
。您必须这样做:
MonthlyOrderViewModel monthlyOrderViewModel = ViewModelProviders.of(this).get(MonthlyOrderViewModel.class);
如果您确定在ViewModel中执行了postValue
,那么我认为这一更改应该可以使它正常工作。还有一件事:您不应该在每次观察到的LiveData通知您某个更改时都这么做。我将在observe()之前移动下一行
更新
正如法希姆在评论中确认的那样,问题在于正在创建同一ViewModel
的多个实例。如果需要共享ViewModel
的同一实例,请确保传递该ViewModel的“所有者”片段/活动的引用。例如,如果MyActivity
有一个MainActivityViewModel
,并且它包含一个名为MyFragment
的子片段,那么如果该片段想要获取对其父视图模型的引用,它必须按照以下方式进行:
MainActivityViewModel mainActivityVM=ViewModelProviders
.of(getActivity())
.get(MainActivityViewModel.class);
是否在片段中为viewmodel设置了LiveCycleOwner?是的,我尝试过。我将monthlyOrderViewModel.getMonthlyOrderHistoryMutableLiveData().observe替换为monthlyOrderViewModel.getMonthlyOrderHistoryMutableLiveData().observe(getViewLifecycleOwner(),monthlyOrderHistory->{
,但结果相同,您在哪里调用fetchMonthlyOrders())
触发将数据加载到您的LiveData
?您提供的代码中没有调用它。是的,我在活动开始时使用此ViewModelProviders.of(this).get(MonthlyOrderViewModel.class).fetchMonthlyOrders();按照您的说明,我尝试了ViewModelProviders.of(this).get(MonthlyOrderViewModel.class).observe
,但没有更改。该程序没有进入inside observe。此外,inside observe中的其余程序只是为了显示我试图用最少的代码实现的目标。如果该程序进入inside observe,我会相应地更改它们的位置。@Fahimalahmudashik我明白了……您是从片段还是视频中观察ViewModel活动?如果保存片段的活动是调用获取的活动,并且您正在片段和活动之间共享ViewModel,那么请尝试使用MonthlyOrderViewModel MonthlyOrderViewModel=ViewModelProviders.of(getActivity()).get(MonthlyOrderViewModel.class)在片段中获取您的ViewModel;
取而代之。如果没有,您将得到两个不同的viewmodel实例抱歉迟到@dglozano。事实上,这就是问题所在,我每次都在重新创建viewmodel的新实例。请编辑您的答案并添加此信息,以便如果其他人遇到此问题,他们可以从您提供的答案中得到明确的答案泰德。我接受你的答案。非常感谢你抽出时间。@Fahimalahmudashik很高兴听到它起作用了!!!我刚刚编辑了答案:)感谢fam,这让我从整整两天的工作中解脱出来,我的数据显示在日志中,但没有显示在我的观察者中,但是在阅读了这篇文章并从拥有viewmodel的片段更改为使用activity的实例之后,我的数据都在这里了。非常感谢
monthlyOrderRecyclerView = view.findViewById(R.id.monthlyOrderRecyclerView);
monthlyOrderRecyclerViewAdapter = new OrderHistoryRecyclerViewAdapter(getContext(), monthlyOrderHistory.getOrders().getUserOrder());
monthlyOrderRecyclerView.setAdapter(monthlyOrderRecyclerViewAdapter);
monthlyOrderRecyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));