重新创建活动时空白屏幕

问题描述

我正在SplashActivity中加载联系人：

private fun startMainActivity() {
        repository.loadContacts()
        handler.postDelayed({
            val intent =Intent(this,MainActivity::class.java)
            startActivity(intent)
            finish()
        },SPLASH_DELAY.toLong())

这是我的存储库类：

@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MainFragment的onCreateView中，我在viewmodel中观察到了LiveData：

                // 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类：

class Contactsviewmodel(repository: ContactsRepository) : viewmodel() {

    private val _liveData = repository.liveData
    val liveData: LiveData<Resource<List<Contact>>>
        get() = _liveData

    /**
     * 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")
        }
    }
}

有时候，当我在很长一段时间后恢复MainFragment时，我会面临一个空屏，RecyclerView中没有数据（例如，容器活动可能被OS杀死）。我的猜测是repository.liveData.value返回null。可能是其他任何问题。感谢您的建议。

附录：

@Inject
Contactsviewmodel.Factory mFactory;

@Override
    public View onCreateView(LayoutInflater inflater,ViewGroup container,Bundle savedInstanceState) {
    Contactsviewmodel viewmodel = new viewmodelProvider(this,mFactory).get(Contactsviewmodel.class);
            ViewDataBinding binding = FragmentContactsBinding.bind(root);
            binding.setvariable(BR.vm,viewmodel);
            binding.setLifecycleOwner(getViewLifecycleOwner());
}

完整的源代码位于：https://github.com/Ali-Rezaei/Contacts/blob/master/app/src/main/java/com/sample/android/contact/ui/ContactsFragment.java

解决方法

我意识到这是由于系统启动的进程死亡。结果，我在ViewModel的init方法中添加了以下代码来解决此问题：

class ContactsViewModel(repository: ContactsRepository) : ViewModel() {

    private val _liveData = repository.liveData
    val liveData: LiveData<Resource<List<Contact>>>
        get() = _liveData

    init {
        // Reload contacts in case of system initiated process death
        if(liveData.value == null) {
            repository.loadContacts()
        }
    }
}