Handling screen rotation without losing data with viewModel - Android

Question

I have one activity with unspecified orientation and there is one fragment attached to that activity that has different layouts for portrait and landscape mode and on that fragment, multiple API calls on a conditional basis, my problem is that when the screen rotates all data was lost and there is a lot of data on that fragment by which I don't want to save each data on saveInstance method. I tried android:configChanges="keyboardHidden|orientation|screenSize", but this didn't solve my problem. I want to handle this problem using viewModel. Please help, Thanks in advance. Here is my code

Repository

class GetDataRepository {
val TAG = GetDataRepository::class.java.canonicalName
var job: CompletableJob = Job()

fun getData(
    token: String?,
    sslContext: SSLContext,
    matchId: Int
): LiveData<ResponseModel> {
    job = Job()
    return object : LiveData<ResponseModel>() {
        override fun onActive() {
            super.onActive()
            job.let { thejob ->
                CoroutineScope(thejob).launch {
                    try {
                        val apiResponse = ApiService(sslContext).getData(
                            token
                         
                        )
                        LogUtil.debugLog(TAG, "apiResponse ${apiResponse}")
                        withContext(Dispatchers.Main) {
                            value = apiResponse
                        }
                    } catch (e: Throwable) {
                        LogUtil.errorLog(TAG, "error: ${e.message}")
                        withContext(Dispatchers.Main) {
                            when (e) {
                                is HttpException -> {
                                    value =
                                        Gson().fromJson<ResponseModel>(
                                            (e as HttpException).response()?.errorBody()
                                                ?.string(),
                                            ResponseModel::class.java
                                        )
                                }
                                else -> value = ResponseModel(error = e)
                            }
                        }

                    } finally {
                        thejob.complete()
                    }
                }

            }
        }
    }
}

fun cancelJob() {
    job.cancel()
}

}

ViewMode:

class DataViewModel : ViewModel() {
val TAG = DataViewModel::class.java.canonicalName
var mListener: DataListener? = null

private val mGetDataRepository: GetDataRepository = GetDataRepository()


fun getData() {
    LogUtil.debugLog(TAG, "getData")
    if (mListener?.isInternetAvailable()!!) {
        mListener?.onStartAPI()

        val context = mListener?.getContext()

        val token: String? = String.format(
            context?.resources!!.getString(R.string.user_token),
            PreferenceUtil.getUserData(context).token
        )

        val sslContext = mListener?.getSSlContext()

        if (sslContext != null) {
            val getData =
                mGetDataRepository.getData(
                    token
                )
            LogUtil.debugLog(TAG, "getData ${getData}")
            mListener?.onApiCall(getData)
        } else {
            LogUtil.debugLog(TAG, "getData Invalid certificate")
            mListener?.onError("Invalid certificate")
        }
    } else {
        LogUtil.debugLog(TAG, "getData No internet")
        mListener?.onError("Please check your internet connectivity!!!")
    }
    LogUtil.debugLog(TAG, "Exit getData()")
}

}

Activity:

class DataActivity : AppCompatActivity() {
val TAG = DataActivity::class.java.canonicalName
lateinit var fragment: DataFragment

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    LogUtil.debugLog(TAG, "onCreate: Enter")

    var binding: ActivityDataBinding =
        DataBindingUtil.setContentView(this, R.layout.activity_data)
    if (savedInstanceState == null) {
         fragment = DataFragment.newInstance()
        supportFragmentManager.beginTransaction().add(R.id.container, fragment, DataFragment.TAG)
    } else {
        fragment = supportFragmentManager.findFragmentByTag(DataFragment.TAG) as DataFragment
    }

    LogUtil.debugLog(TAG, "onCreate: Exit")
}

}

Fragment:

class DataFragment : Fragment(), DataListener {
private var mBinding: FragmentDataBinding? = null
private lateinit var mViewModel: DataViewModel

companion object {
    val TAG = DataFragment::class.java.canonicalName
    fun newInstance(): DataFragment {
        return DataFragment()
    }
}

override fun onCreateView(
    inflater: LayoutInflater,
    container: ViewGroup?,
    savedInstanceState: Bundle?
): View? {
    mBinding =
        DataBindingUtil.inflate(inflater, R.layout.fragment_data, container, false)
    mViewModel = ViewModelProvider(this).get(DataViewModel::class.java)
    mViewModel.mListener = this
    getData()
    return mBinding?.root
}

private fun getData() {
    LogUtil.debugLog(TAG, "Enter getMatchScore()")
    mViewModel.getData()
    LogUtil.debugLog(TAG, "Exit getMatchScore()")
}

override fun <T> onApiCall(response: LiveData<T>) {
    response.observe(this, Observer {
        it as DataResponseModel
        //
    })

}

}

Answer 1

The lifecycle of viewModel by default is longer than your activity (in your case, screen rotation).

ViewModel will not be destroyed as soon as activity destroyed for configuration change, you can see this link.

You seem to have made a mistake elsewhere in your activity/fragment, please put your activity/fragment code here.

In your fragment you call mViewModel.getData() in your onCreateView, and every time you rotate your activity, this method call and all store data reset and fetched again!, simply you can check data of ViewModel in your fragment and if it's empty call getData(), it also seems your ViewModel reference to your view(Fragment) (you pass a listener from your fragment to your ViewModel) and it is also an anti-pattern (This article is recommended)