问题所在
我正在开发一个使用Kotlin合成绑定、RxJava、Retrofit和MVP模式的安卓应用程序。在这个应用程序上有一个屏幕,它应该从API中获取一些数据,并用返回的数据填充RecyclerView
。
所有这些都是有效的,直到我试着旋转屏幕...一旦重新创建了活动和片段并尝试访问RecyclerView,应用程序就会崩溃,并出现以下异常:
10-25 18:20:00.368 4580-4580/com.sample.app E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.sample.app, PID: 4580
java.lang.IllegalStateException: recyclerView must not be null
at com.sample.app.features.atendimento.ClientesAtendimentosFragment.onAtendimentosLoaded(ClientesAtendimentosFragment.kt:56)
at com.sample.app.features.atendimento.ClienteAtendimentoActivity.showClientesAtendimento(ClienteAtendimentoActivity.kt:126)
at com.sample.app.features.atendimento.ClienteAtendimentoPresenter$getClientesAtendimento$3.accept(ClienteAtendimentoPresenter.kt:38)
at com.sample.app.features.atendimento.ClienteAtendimentoPresenter$getClientesAtendimento$3.accept(ClienteAtendimentoPresenter.kt:18)
at io.reactivex.internal.observers.ConsumerSingleObserver.onSuccess(ConsumerSingleObserver.java:63)
at io.reactivex.internal.operators.single.SingleDoAfterTerminate$DoAfterTerminateObserver.onSuccess(SingleDoAfterTerminate.java:71)
当我尝试调用此方法时,就会发生这种情况:
override fun onAtendimentosLoaded(atendimentos: List<UsuarioAtendimento>) {
recyclerView.visibility = View.VISIBLE
recyclerView.adapter = ClienteAtendimentoAdapter(atendimentos, this)
}
由于某些原因,recyclerView变量为空,即使Activity和Fragment都已成功创建并在手机上可见(我甚至可以在崩溃前看到加载屏幕),应用程序也会崩溃。
那么,为什么即使在活动和片段已经可见之后,我的视图仍然是空的?
编辑:我也添加了MVP文件,以帮助理解这里发生的事情。
Presenter
class ClienteAtendimentoPresenter(private val repository: ClienteAtendimentoRepository): ClienteAtendimentoContract.Presenter {
private var view: ClienteAtendimentoContract.View? = null
private var disposable: Disposable? = null
override fun getClientesAtendimento() {
try {
disposable = repository.getClientesEmAtendimento()
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.doOnSubscribe {
view?.hideErrors()
view?.showLoading()
}
.doAfterTerminate {
view?.hideLoading()
}
.subscribe(
{
view?.showClientesAtendimento(it)
},
{
handleError(it)
}
)
} catch (e: NoConnectionException) {
view?.hideLoading()
handleError(e)
}
}
override fun stop() {
view = null
disposable?.dispose()
}
override fun attachView(view: BaseView<BasePresenter>) {
if (view is ClienteAtendimentoContract.View)
this.view = view
}
}
视图
class ClienteAtendimentoActivity : BaseActivity(), ClienteAtendimentoContract.View {
override val presenter: ClienteAtendimentoContract.Presenter by inject()
private lateinit var mSectionsPagerAdapter: SectionsPagerAdapter
inner class SectionsPagerAdapter(fm: FragmentManager) : FragmentPagerAdapter(fm) {
private val fragAtendimento = ClientesAtendimentosFragment.newInstance()
private val fragEspera = ClientesAtendimentosFragment.newInstance()
override fun getItem(position: Int): Fragment {
return if (position == 0) fragAtendimento else fragEspera
}
override fun getCount(): Int = 2
}
private fun setupTabs() {
mSectionsPagerAdapter = SectionsPagerAdapter(supportFragmentManager)
// Set up the ViewPager with the sections adapter.
container.adapter = mSectionsPagerAdapter
container.addOnPageChangeListener(TabLayout.TabLayoutOnPageChangeListener(tabs))
tabs.addOnTabSelectedListener(TabLayout.ViewPagerOnTabSelectedListener(container))
}
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_cliente_atendimento)
// ...
setupTabs()
}
override fun onResume() {
super.onResume()
presenter.attachView(this)
presenter.getClientesAtendimento()
}
override fun onPause() {
super.onPause()
presenter.stop()
}
// ...
override fun showClientesAtendimento(atendimentos: AtendimentosLista) {
val atendimentosFrag = mSectionsPagerAdapter.getItem(0) as ClientesAtendimentosFragment
val filaEsperaFrag = mSectionsPagerAdapter.getItem(1) as ClientesAtendimentosFragment
atendimentosFrag.onAtendimentosLoaded(atendimentos.atendimentos) // This is where I'm getting the error.
filaEsperaFrag.onAtendimentosLoaded(atendimentos.espera)
}
// ...
}
片段
class ClientesAtendimentosFragment : Fragment(), AtendimentosFragmentCallback, OnClickAtendimentoCallback {
private lateinit var recyclerView: RecyclerView
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?): View? {
val rootView = inflater.inflate(R.layout.fragment_single_rv, container, false)
recyclerView = rootView.findViewById(R.id.recyclerView) // I did this to test if Kotlin synthetic binding was the problem.
return rootView
}
// ...
override fun onAtendimentosLoaded(atendimentos: List<UsuarioAtendimento>) {
recyclerView.visibility = View.VISIBLE // App is crashing here.
recyclerView.adapter = ClienteAtendimentoAdapter(atendimentos, this)
}
// ...
}
我到目前为止所尝试的
按照this answer上的建议,我尝试让片段保留实例,但这不起作用。
我还尝试抛弃了Kotlin合成绑定,并将recyclerView变量设置为在onCreateView()
方法中膨胀的lateinit var
,如下面的代码片段所示:
private lateinit var recyclerView: RecyclerView
//...
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?): View? {
val rootView = inflater.inflate(R.layout.fragment_single_rv, container, false)
recyclerView = rootView.findViewById(R.id.recyclerView)
return rootView
}
但是现在我得到了以下错误:
10-25 18:32:42.261 10572-10572/com.sample.app E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.sample.app, PID: 10572
io.reactivex.exceptions.UndeliverableException: kotlin.UninitializedPropertyAccessException: lateinit property recyclerView has not been initialized
at io.reactivex.plugins.RxJavaPlugins.onError(RxJavaPlugins.java:367)
at io.reactivex.internal.observers.ConsumerSingleObserver.onSuccess(ConsumerSingleObserver.java:66)
at io.reactivex.internal.operators.single.SingleDoAfterTerminate$DoAfterTerminateObserver.onSuccess(SingleDoAfterTerminate.java:71)
at io.reactivex.internal.operators.single.SingleDoOnSubscribe$DoOnSubscribeSingleObserver.onSuccess(SingleDoOnSubscribe.java:77)
at io.reactivex.internal.operators.single.SingleObserveOn$ObserveOnSingleObserver.run(SingleObserveOn.java:81)
at io.reactivex.android.schedulers.HandlerScheduler$ScheduledRunnable.run(HandlerScheduler.java:119)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:145)
at android.app.ActivityThread.main(ActivityThread.java:6939)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1404)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1199)
Caused by: kotlin.UninitializedPropertyAccessException: lateinit property recyclerView has not been initialized
at com.sample.app.features.atendimento.ClientesAtendimentosFragment.onAtendimentosLoaded(ClientesAtendimentosFragment.kt:59)
编辑:我做了Xite suggested on his answer,我发现由于某些原因,当我旋转屏幕时,新的Rx调用仍然试图使用旧的片段引用,即使新的片段已经成功创建并显示。我不知道我应该在哪里清理它,或者为什么它会这样做,也许它与supportFragmentManager
有关
发布于 2018-10-26 22:13:46
经过一些挖掘,以及这里一些答案的帮助,我找到了this post on Medium,它引导我找到了解决方案。
所以,是的,问题出在FragmentPagerAdapter
上,它返回一个旧的片段实例,这会导致空指针。
为了解决这个问题,首先我将创建片段的方式更改为:
inner class SectionsPagerAdapter(fm: FragmentManager) : FragmentPagerAdapter(fm) {
private val fragList = ArrayList<Fragment>()
fun addFragment(frag: Fragment) {
fragList.add(frag)
}
override fun getItem(position: Int): Fragment {
return fragList[position]
}
override fun getCount(): Int = fragList.size
}
然后,我必须覆盖适配器内部的instantiateItem(container: ViewGroup, position: Int)
方法,并使其如下所示:
override fun instantiateItem(container: ViewGroup, position: Int): Any {
val ret = super.instantiateItem(container, position)
fragList[position] = ret as Fragment
return ret
}
至于为什么会发生这种情况,this answer on SO解释得很好。
发布于 2018-10-26 05:55:12
首先,尝试对其进行调试,并在旋转之前和之后在onAtendimentosLoaded()
中查找片段的哈希码(this
)。假设您没有使用setRetainInstance
,那么它们应该是不同的。如果它们是相同的,你没有正确地清除一些东西,很难确切地说出是什么导致了这个问题,因为我们没有相关的片段、活动和演示者代码。
发布于 2018-10-26 21:10:09
我认为问题出在你的SectionsPagerAdapter.getItem
中,你应该总是实例化一个新的片段:
override fun getItem(position: Int): Fragment {
return if (position == 0) ClientesAtendimentosFragment.newInstance() else ClientesAtendimentosFragment.newInstance()
}
我知道FragmentPagerAdapter
的文档并不清楚,但是如果你看看它的instantiateItem
方法:
@Override
public Object instantiateItem(ViewGroup container, int position) {
if (mCurTransaction == null) {
mCurTransaction = mFragmentManager.beginTransaction();
}
final long itemId = getItemId(position);
// Do we already have this fragment?
String name = makeFragmentName(container.getId(), itemId);
Fragment fragment = mFragmentManager.findFragmentByTag(name);
if (fragment != null) {
if (DEBUG) Log.v(TAG, "Attaching item #" + itemId + ": f=" + fragment);
mCurTransaction.attach(fragment);
} else {
fragment = getItem(position); // @Mauker it requires a new fragment instance!
if (DEBUG) Log.v(TAG, "Adding item #" + itemId + ": f=" + fragment);
mCurTransaction.add(container.getId(), fragment,
makeFragmentName(container.getId(), itemId));
}
if (fragment != mCurrentPrimaryItem) {
fragment.setMenuVisibility(false);
fragment.setUserVisibleHint(false);
}
return fragment;
}
很明显,无论何时调用SectionsPagerAdapter.getItem
,我们都需要提供一个新的片段实例。因此,在您的示例中,当屏幕旋转时,适配器(假设适配器是持久化的)将返回片段的旧引用,这些片段的视图可能已经被销毁。
而且你不应该在之后调用getItem
,它应该只被适配器使用,当你调用它时,它只会一直返回新的片段实例。
如果你真的需要获取参考资料,那么尝试如下所示:
val fragments = SparseArray<Fragment>()
fun getFragment(position: Int): Fragment? { // call this instead
return fragments.get(position)
}
override fun getItem(position: Int): Fragment {
val fragment = SomeFragment()
fragments.put(position, fragment) // store it for later use
return fragment
}
我希望它能工作,祝你好运!
https://stackoverflow.com/questions/52997700
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