title: (Kotlin) I want to retrieve data from realtime database(firebase) without using addValueEventListener
body: <p>I want to get data from firebase and put into array to make a list for recyclerView.
  In database, there are news title, img source and link.</p>
  <pre><code>val firebaseDatabase: FirebaseDatabase = FirebaseDatabase.getInstance()
  val rootRef: DatabaseReference = firebaseDatabase.getReference(&quot;20210107&quot;)
  val justList = ArrayList&lt;justInfo&gt;()
  rootRef.addValueEventListener(object : ValueEventListener{
      override fun onDataChange(snapshot: DataSnapshot){
          var title : String = snapshot.child(&quot;title&quot;).getValue().toString()
          var link : String = snapshot.child(&quot;link&quot;).getValue().toString()
          var imgSrc: String = snapshot.child(&quot;img&quot;).getValue().toString()
          justList.add(justInfo(title, link, imgSrc))
      }
      override fun onCancelled(error: DatabaseError){
      }
  })
  </code></pre>
  <p>I don't want to detect the change on Database. I just want to pull existing data from DB.
  What should I do?</p>