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QueryActivity.kt
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QueryActivity.kt
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package com.google.firebase.referencecode.database.kotlin
import android.os.Bundle
import android.util.Log
import android.widget.Toast
import androidx.appcompat.app.AppCompatActivity
import com.google.firebase.database.ChildEventListener
import com.google.firebase.database.DataSnapshot
import com.google.firebase.database.DatabaseError
import com.google.firebase.database.DatabaseReference
import com.google.firebase.database.Query
import com.google.firebase.database.ValueEventListener
import com.google.firebase.database.database
import com.google.firebase.database.getValue
import com.google.firebase.Firebase
import com.google.firebase.referencecode.database.R
import com.google.firebase.referencecode.database.kotlin.models.Comment
import com.google.firebase.referencecode.database.models.Message
/**
* Kotlin verison of {@link QueryActivity].
*/
abstract class QueryActivity : AppCompatActivity() {
companion object {
private const val TAG = "KotlinQueryActivity"
}
private lateinit var messagesRef: DatabaseReference
private lateinit var databaseReference: DatabaseReference
private lateinit var messagesQuery: Query
private lateinit var messagesListener: ValueEventListener
private lateinit var messagesQueryListener: ChildEventListener
var uid: String = "42"
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_query)
databaseReference = Firebase.database.reference
}
private fun basicListen() {
// [START basic_listen]
// Get a reference to Messages and attach a listener
messagesRef = databaseReference.child("messages")
messagesListener = object : ValueEventListener {
override fun onDataChange(dataSnapshot: DataSnapshot) {
// New data at this path. This method will be called after every change in the
// data at this path or a subpath.
Log.d(TAG, "Number of messages: ${dataSnapshot.childrenCount}")
for (child in dataSnapshot.children) {
// Extract Message object from the DataSnapshot
val message: Message? = child.getValue<Message>()
// Use the message
// [START_EXCLUDE]
Log.d(TAG, "message text: ${message?.text}")
Log.d(TAG, "message sender name: ${message?.name}")
// [END_EXCLUDE]
}
}
override fun onCancelled(error: DatabaseError) {
// Could not successfully listen for data, log the error
Log.e(TAG, "messages:onCancelled: ${error.message}")
}
}
messagesRef.addValueEventListener(messagesListener)
// [END basic_listen]
}
private fun basicQuery() {
// [START basic_query]
// My top posts by number of stars
val myUserId = uid
val myTopPostsQuery = databaseReference.child("user-posts").child(myUserId)
.orderByChild("starCount")
myTopPostsQuery.addChildEventListener(object : ChildEventListener {
// TODO: implement the ChildEventListener methods as documented above
// [START_EXCLUDE]
override fun onChildAdded(dataSnapshot: DataSnapshot, s: String?) {}
override fun onChildChanged(dataSnapshot: DataSnapshot, s: String?) {}
override fun onChildRemoved(dataSnapshot: DataSnapshot) {}
override fun onChildMoved(dataSnapshot: DataSnapshot, s: String?) {}
override fun onCancelled(databaseError: DatabaseError) {}
// [END_EXCLUDE]
})
// [END basic_query]
}
private fun basicQueryValueListener() {
val myUserId = uid
val myTopPostsQuery = databaseReference.child("user-posts").child(myUserId)
.orderByChild("starCount")
// [START basic_query_value_listener]
// My top posts by number of stars
myTopPostsQuery.addValueEventListener(object : ValueEventListener {
override fun onDataChange(dataSnapshot: DataSnapshot) {
for (postSnapshot in dataSnapshot.children) {
// TODO: handle the post
}
}
override fun onCancelled(databaseError: DatabaseError) {
// Getting Post failed, log a message
Log.w(TAG, "loadPost:onCancelled", databaseError.toException())
// ...
}
})
// [END basic_query_value_listener]
}
private fun cleanBasicListener() {
// Clean up value listener
// [START clean_basic_listen]
messagesRef.removeEventListener(messagesListener)
// [END clean_basic_listen]
}
private fun cleanBasicQuery() {
// Clean up query listener
// [START clean_basic_query]
messagesQuery.removeEventListener(messagesQueryListener)
// [END clean_basic_query]
}
fun orderByNested() {
// [START rtdb_order_by_nested]
// Most viewed posts
val myMostViewedPostsQuery = databaseReference.child("posts")
.orderByChild("metrics/views")
myMostViewedPostsQuery.addChildEventListener(object : ChildEventListener {
// TODO: implement the ChildEventListener methods as documented above
// [START_EXCLUDE]
override fun onChildAdded(dataSnapshot: DataSnapshot, s: String?) {}
override fun onChildChanged(dataSnapshot: DataSnapshot, s: String?) {}
override fun onChildRemoved(dataSnapshot: DataSnapshot) {}
override fun onChildMoved(dataSnapshot: DataSnapshot, s: String?) {}
override fun onCancelled(databaseError: DatabaseError) {}
// [END_EXCLUDE]
})
// [END rtdb_order_by_nested]
}
private fun childEventListenerRecycler() {
val context = this
// [START child_event_listener_recycler]
val childEventListener = object : ChildEventListener {
override fun onChildAdded(dataSnapshot: DataSnapshot, previousChildName: String?) {
Log.d(TAG, "onChildAdded:" + dataSnapshot.key!!)
// A new comment has been added, add it to the displayed list
val comment = dataSnapshot.getValue<Comment>()
// ...
}
override fun onChildChanged(dataSnapshot: DataSnapshot, previousChildName: String?) {
Log.d(TAG, "onChildChanged: ${dataSnapshot.key}")
// A comment has changed, use the key to determine if we are displaying this
// comment and if so displayed the changed comment.
val newComment = dataSnapshot.getValue<Comment>()
val commentKey = dataSnapshot.key
// ...
}
override fun onChildRemoved(dataSnapshot: DataSnapshot) {
Log.d(TAG, "onChildRemoved:" + dataSnapshot.key!!)
// A comment has changed, use the key to determine if we are displaying this
// comment and if so remove it.
val commentKey = dataSnapshot.key
// ...
}
override fun onChildMoved(dataSnapshot: DataSnapshot, previousChildName: String?) {
Log.d(TAG, "onChildMoved:" + dataSnapshot.key!!)
// A comment has changed position, use the key to determine if we are
// displaying this comment and if so move it.
val movedComment = dataSnapshot.getValue<Comment>()
val commentKey = dataSnapshot.key
// ...
}
override fun onCancelled(databaseError: DatabaseError) {
Log.w(TAG, "postComments:onCancelled", databaseError.toException())
Toast.makeText(
context,
"Failed to load comments.",
Toast.LENGTH_SHORT,
).show()
}
}
databaseReference.addChildEventListener(childEventListener)
// [END child_event_listener_recycler]
}
private fun recentPostsQuery() {
// [START recent_posts_query]
// Last 100 posts, these are automatically the 100 most recent
// due to sorting by push() keys.
databaseReference.child("posts").limitToFirst(100)
// [END recent_posts_query]
}
override fun onStart() {
super.onStart()
basicListen()
basicQuery()
basicQueryValueListener()
}
override fun onStop() {
super.onStop()
cleanBasicListener()
cleanBasicQuery()
}
}