CODEWITHSUNDEEP
androidkotlin
Sai
Sai

Reputation: 15718

How can i avoid null properties in Kotlin

I am using Kotlin from quite some time now, but I could not able to achieve not-null types for all the properties in Kotlin.

Please take a look at below code, there are some scenarios where I have to use null types. I know I can use lateinit but in some scenarios, it does not fit. How can I avoid null in my code?

If anyone can re-write the code with without null types or correct my mistakes, it is more than enough for me to understand everything.

class MusicService : Service(), PlaybackManager.PlaybackServiceCallback {

    private val mDelayedStopHandler = DelayedStopHandler(this)
    private val eventBus = EventBus.getDefault()

    //How to avoid nullable types
    private var mMediaNotificationManager: MediaNotificationManager? = null
    private var mSession: MediaSessionCompat? = null
    var mSessionToken: MediaSessionCompat.Token? = null
    var mPlaybackManager: PlaybackManager? = null
    var mTransportControls: MediaControllerCompat.TransportControls? = null

    override fun onCreate() {
        Timber.d("onCreate")
        super.onCreate()

        //Init MediaSessionCompat and TransportControls
        mSession = MediaSessionCompat(this, "MusicService")
        mSessionToken = mSession?.sessionToken
        mSession?.setFlags(MediaSessionCompat.FLAG_HANDLES_MEDIA_BUTTONS or MediaSessionCompat.FLAG_HANDLES_TRANSPORT_CONTROLS)
        mTransportControls = MediaControllerCompat(this, mSession).transportControls

        //EventBus Reg
        eventBus.reg(this)
        eventBus.post(GetAllMediaEventRequest())
    }

    @Subscribe
    fun onGetAllMediaEventResponse(event: GetAllMediaEventResponse) {
        Timber.d("GetAllMediaEventResponse event.status = ", event.status)

        //init PlaybackManager
        mPlaybackManager = PlaybackManager(mPlayback = LocalPlayer(this),
                mMediaData = event.mediaItems,
                mServiceCallback = this)
        mSession?.setCallback(mPlaybackManager!!.mMediaSessionCallback)


        //Init Notification
        try {
            mMediaNotificationManager = MediaNotificationManager(this)
        } catch (e: RemoteException) {
            throw IllegalStateException("Could not create a MediaNotificationManager", e)
        }
    }
}

Update:

Thanks for all the response which I've got. After a bit of research, I made all properties not nullable. Please check my code and correct me if any mistakes.

class MusicService : Service(), PlaybackManager.PlaybackServiceCallback {

    //NotNull
    private val mDelayedStopHandler = DelayedStopHandler(this)
    private val eventBus = EventBus.getDefault()

    //Lateinit
    lateinit var mSessionToken: MediaSessionCompat.Token
    lateinit var mTransportControls: MediaControllerCompat.TransportControls

    //Lazy
    private val mSession: MediaSessionCompat by lazy { MediaSessionCompat(this, "MusicService") }
    private val mMediaNotificationManager: MediaNotificationManager by lazy {
        try {
            MediaNotificationManager(this)
        } catch (e: RemoteException) {
            throw IllegalStateException("Could not create a MediaNotificationManager", e)
        }
    }
    val mPlaybackManager: PlaybackManager by lazy {
        PlaybackManager(mPlayback = LocalPlayer(this), mServiceCallback = this)
    }

    override fun onCreate() {
        LogHelper.d(TAG, "onCreate")
        super.onCreate()

        //Init MediaSessionCompat and TransportControls
        mSessionToken = mSession.sessionToken
        mSession.setFlags(MediaSessionCompat.FLAG_HANDLES_MEDIA_BUTTONS or MediaSessionCompat.FLAG_HANDLES_TRANSPORT_CONTROLS)
        mTransportControls = MediaControllerCompat(this, mSession).transportControls
        mSession.setCallback(mPlaybackManager.mMediaSessionCallback)

        //EventBus Reg
        eventBus.reg(this)
        eventBus.post(GetAllMediaEventRequest())

    }

    @Subscribe
    fun onGetAllMediaEventResponse(event: GetAllMediaEventResponse) {
        Timber.d("GetAllMediaEventResponse event.status = ", event.status)
        mPlaybackManager.mMediaData = event.mediaItems
    }
}

Upvotes: 0

Views: 356

Answers (1)

ice1000
ice1000

Reputation: 6569

I guess you might need some

a?.let {
  println(it)
  // if `a` isn't null, the code will reach here
  // and `it` will hold the value of `a`
  // you can do a lot of things here without checking if it is null
}

Upvotes: 1

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