KotlinNullException when using query - firebase

Question

i'm trying to build an app that shows images from FirebaseDatabase into RecyclerView, something like this tutorial but with Kotlin, now I have kotlin.KotlinNullPointerException and it points to this code line
var options = FirebaseRecyclerOptions.Builder<Blog>()
.setQuery(query!!, Blog::class.java)
.build()
I couldn't solve it since tow days, this is the activity code :
class MainActivity : AppCompatActivity() {
private var mDatabase:DatabaseReference? = null
private var mBlogList:RecyclerView?=null
private var query:Query?=null
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
navBar.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener)
mDatabase=FirebaseDatabase.getInstance().getReference().child("mall")
mDatabase?.keepSynced(true)
mBlogList = findViewById(R.id.recyclee)
mBlogList?.setHasFixedSize(true)
mBlogList?.layoutManager = LinearLayoutManager(this)
query = mDatabase?.orderByKey()
}
var options = FirebaseRecyclerOptions.Builder<Blog>()
.setQuery(query!!, Blog::class.java)
.build()
override fun onStart() {
super.onStart()
val mAdapter = object : FirebaseRecyclerAdapter<Blog, BlogViewHolder>(
options) {
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): BlogViewHolder {
val view = LayoutInflater.from(parent.context)
.inflate(R.layout.cardview, parent, false)
return BlogViewHolder(view)}
override fun onBindViewHolder(holder: BlogViewHolder, position: Int, model: Blog) {
holder.setTitle(model.title)
holder.setDes(model.des)
holder.setImage(applicationContext, model.image)
}
}
mBlogList?.adapter = mAdapter
}
inner class BlogViewHolder : RecyclerView.ViewHolder{
var mView:View?=null
constructor(itemView: View?) : super(itemView) {
this.mView = itemView
}
fun setTitle(title:String){
var postTitle = mView?.findViewById<TextView>(R.id.post_title)
postTitle?.text = title
}
fun setDes(des:String){
var postDes = mView?.findViewById<TextView>(R.id.post_des)
postDes?.text = des
}
fun setImage(ctx:Context, image:String){
var postImage = mView?.findViewById<ImageView>(R.id.post_title)
Picasso.get().load(image).into(postImage)
}
}
}
Blog class:
class Blog(var title: String?, var des: String?, var image: String?)
My database looks like:

Answer 1

You're trying to make use of query before it's initially assigned in onCreate. You should wait to create options only after query has a non-null value. Notice that your options is sitting at the class member level, which gets evaluated before Android calls your onCreate.