问题描述
我正在SplashActivity的“存储库”层中加载联系人：
@Inject
lateinit var repository: ContactsRepository
private fun startMainActivity() {
repository.loadContacts()
handler.postDelayed({
val intent =Intent(this,MainActivity::class.java)
startActivity(intent)
finish()
},SPLASH_DELAY.toLong())
}
这是我的存储库：
@Singleton
class ContactsRepository @Inject constructor(
private val context: Context,private val schedulerProvider: BaseSchedulerProvider) {
private val compositedisposable = Compositedisposable()
private val _liveData = mutablelivedata<Resource<List<Contact>>>()
val liveData: LiveData<Resource<List<Contact>>>
get() = _liveData
fun loadContacts() {
_liveData.value = Resource.Loading()
val cursor = context.contentResolver.query(
ContactsContract.CommonDataKinds.Phone.CONTENT_URI,PROJECTION,null,ContactsContract.CommonDataKinds.Phone.disPLAY_NAME + " COLLATE UNICODE ASC")
Observable.create(ObservableOnSubscribe<List<Contact>>
{ emitter -> emitter.onNext(ContactUtil.getContacts(cursor,context)) })
.subscribeOn(schedulerProvider.io())
.doOnComplete { cursor?.close() }
.doFinally { compositedisposable.clear() }
.subscribe {
_liveData.postValue(Resource.Success(it))
}.also { compositedisposable.add(it) }
}
}
在我的ContactsFragment中，我初始化了viewmodel：
@Override
public View onCreateView(LayoutInflater inflater,ViewGroup container,Bundle savedInstanceState) {
Log.d(TAG,"onCreateView()");
View root = inflater.inflate(R.layout.fragment_contacts,container,false);
Contactsviewmodel viewmodel = new viewmodelProvider(this,mFactory).get(Contactsviewmodel.class);
FragmentContactsBinding binding = FragmentContactsBinding.bind(root);
binding.setvariable(BR.vm,viewmodel);
binding.setLifecycleOwner(getViewLifecycleOwner());
// Create the observer which updates the UI.
final Observer<Resource<List<Contact>>> contactsObserver = resource -> {
if (resource instanceof Resource.Success) {
mContacts = ((Resource.Success<List<Contact>>) resource).getData();
mAdapter.setItems(mContacts,true);
}
};
// Observe the LiveData,passing in this fragment as the LifecycleOwner and the observer.
viewmodel.getLiveData().observe(this,contactsObserver);
}
这是我的viewmodel：
class Contactsviewmodel(repository: ContactsRepository) : viewmodel() {
private val _liveData = repository.liveData
val liveData: LiveData<Resource<List<Contact>>>
get() = _liveData
init {
if(repository.liveData.value == null) {
repository.loadContacts()
}
}
/**
* Factory for constructing Contactsviewmodel with parameter
*/
class Factory @Inject constructor(
private val repository: ContactsRepository
) : viewmodelProvider.Factory {
override fun <T : viewmodel?> create(modelClass: Class<T>): T {
if (modelClass.isAssignableFrom(Contactsviewmodel::class.java)) {
@Suppress("UNCHECKED_CAST")
return Contactsviewmodel(repository) as T
}
throw IllegalArgumentException("Unable to construct viewmodel")
}
}
}
如您所见，有时我在很长一段时间后恢复应用程序时，“ repository.liveData.value”返回null，结果我在viewmodel中具有以下逻辑：
init {
if(repository.liveData.value == null) {
repository.loadContacts()
}
}
有更好的解决方案吗？
可以找到完整的源代码：https://github.com/Ali-Rezaei/Contacts
解决方法
我认为这可能会发生，因为系统对您的应用程序进行了GC。当设备内存不足时，可能会发生这种情况。 ViewModel将仅在配置更改后幸存，而不会在应用程序终止后幸存。要解决此问题，您需要在loadContacts时在ContactsFragment#onCreateView中调用savedInstanceState != null。
ViewModels无法幸免于系统启动的进程死亡。要解决此问题，您需要使用SavedStateHandle：
https://developer.android.com/reference/androidx/lifecycle/SavedStateHandle
例如，在下面链接的FilterViewModel中，我使用SavedStateHandle存储一组索引，并在SavedStateHandle不为null的情况下检索它们（仅在系统启动的情况下才为非null）死亡）：