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Kotlin snippets for queries (firebase#11)
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‎database/app/src/main/java/com/google/firebase/referencecode/database/KotlinQueryActivity.kt‎

Lines changed: 140 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,140 @@
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package com.google.firebase.referencecode.database
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import android.os.Bundle
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import android.support.v7.app.AppCompatActivity
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import android.util.Log
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import com.google.firebase.database.*
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import com.google.firebase.referencecode.database.interfaces.QueryActivityInterface
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import com.google.firebase.referencecode.database.models.Message
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/**
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* Kotlin verison of {@link QueryActivity].
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*/
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class KotlinQueryActivity : AppCompatActivity(), QueryActivityInterface {
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companion object {
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private val TAG = "KotlinQueryActivity"
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}
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private lateinit var messagesRef: DatabaseReference
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private lateinit var databaseReference: DatabaseReference
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private lateinit var messagesQuery: Query
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private lateinit var messagesListener: ValueEventListener
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private lateinit var messagesQueryListener: ChildEventListener
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override fun onCreate(savedInstanceState: Bundle?) {
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super.onCreate(savedInstanceState)
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setContentView(R.layout.activity_query)
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databaseReference = FirebaseDatabase.getInstance().reference
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}
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override fun getUid(): String {
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return "42"
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}
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override fun basicListen() {
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// [START basic_listen]
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// Get a reference to Messages and attach a listener
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messagesRef = databaseReference.child("messages")
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messagesListener = object : ValueEventListener {
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override fun onDataChange(dataSnapshot: DataSnapshot) {
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// New data at this path. This method will be called after every change in the
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// data at this path or a subpath.
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Log.d(TAG, "Number of messages: ${dataSnapshot.childrenCount}")
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dataSnapshot.children?.forEach { child ->
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// Extract Message object from the DataSnapshot
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val message: Message? = child.getValue(Message::class.java)
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// Use the message
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// [START_EXCLUDE]
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Log.d(TAG, "message text: ${message?.text}")
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Log.d(TAG, "message sender name: ${message?.name}")
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// [END_EXCLUDE]
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}
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}
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override fun onCancelled(error: DatabaseError) {
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// Could not successfully listen for data, log the error
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Log.e(TAG, "messages:onCancelled: ${error.message}")
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}
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}
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messagesRef.addValueEventListener(messagesListener)
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// [END basic_listen]
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}
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override fun basicQuery() {
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// [START basic_query]
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// My top posts by number of stars
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val myUserId = uid
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val myTopPostsQuery = databaseReference.child("user-posts").child(myUserId)
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.orderByChild("starCount")
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myTopPostsQuery.addChildEventListener(object : ChildEventListener {
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// TODO: implement the ChildEventListener methods as documented above
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// [START_EXCLUDE]
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override fun onChildAdded(dataSnapshot: DataSnapshot, s: String) {}
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override fun onChildChanged(dataSnapshot: DataSnapshot, s: String) {}
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override fun onChildRemoved(dataSnapshot: DataSnapshot) {}
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override fun onChildMoved(dataSnapshot: DataSnapshot, s: String) {}
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override fun onCancelled(databaseError: DatabaseError) {}
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// [END_EXCLUDE]
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})
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// [END basic_query]
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}
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override fun basicQueryValueListener() {
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val myUserId = uid
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val myTopPostsQuery = databaseReference.child("user-posts").child(myUserId)
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.orderByChild("starCount")
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// [START basic_query_value_listener]
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// My top posts by number of stars
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myTopPostsQuery.addValueEventListener(object : ValueEventListener {
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override fun onDataChange(dataSnapshot: DataSnapshot) {
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for (postSnapshot in dataSnapshot.children) {
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// TODO: handle the post
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}
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}
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override fun onCancelled(databaseError: DatabaseError) {
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// Getting Post failed, log a message
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Log.w(TAG, "loadPost:onCancelled", databaseError.toException())
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// ...
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}
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})
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// [END basic_query_value_listener]
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}
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override fun cleanBasicListener() {
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// Clean up value listener
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// [START clean_basic_listen]
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messagesRef.removeEventListener(messagesListener)
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// [END clean_basic_listen]
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}
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override fun cleanBasicQuery() {
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// Clean up query listener
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// [START clean_basic_query]
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messagesQuery.removeEventListener(messagesQueryListener)
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// [END clean_basic_query]
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}
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override fun onStart() {
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super.onStart()
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basicListen()
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basicQuery()
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basicQueryValueListener()
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}
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override fun onStop() {
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super.onStop()
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cleanBasicListener()
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cleanBasicQuery()
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}
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}

‎database/app/src/main/java/com/google/firebase/referencecode/database/QueryActivity.java‎

Lines changed: 34 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -26,6 +26,7 @@
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import com.google.firebase.database.FirebaseDatabase;
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import com.google.firebase.database.Query;
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import com.google.firebase.database.ValueEventListener;
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import com.google.firebase.referencecode.database.interfaces.QueryActivityInterface;
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import com.google.firebase.referencecode.database.models.Message;
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/**
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*
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* Use {@link MainActivity} to populate the Message data.
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*/
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public class QueryActivity extends AppCompatActivity {
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public class QueryActivity extends AppCompatActivity implements QueryActivityInterface {
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3940
private static final String TAG = "QueryActivity";
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@@ -54,14 +55,13 @@ protected void onCreate(Bundle savedInstanceState) {
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databaseReference = FirebaseDatabase.getInstance().getReference();
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}
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private String getUid() {
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@Override
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public String getUid() {
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return "42";
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}
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@Override
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public void onStart() {
63-
super.onStart();
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public void basicListen() {
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// [START basic_listen]
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// Get a reference to Messages and attach a listener
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mMessagesRef = databaseReference.child("messages");
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};
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mMessagesRef.addValueEventListener(mMessagesListener);
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// [END basic_listen]
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}
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@Override
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public void basicQuery() {
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// [START basic_query]
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// My top posts by number of stars
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String myUserId = getUid();
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// [END_EXCLUDE]
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});
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// [END basic_query]
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}
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@Override
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public void basicQueryValueListener() {
120+
String myUserId = getUid();
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Query myTopPostsQuery = databaseReference.child("user-posts").child(myUserId)
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.orderByChild("starCount");
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115124
// [START basic_query_value_listener]
116125
// My top posts by number of stars
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}
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});
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// [END basic_query_value_listener]
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}
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136144
@Override
137-
public void onStop() {
138-
super.onStop();
139-
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public void cleanBasicListener() {
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// Clean up value listener
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// [START clean_basic_listen]
142148
mMessagesRef.removeEventListener(mMessagesListener);
143149
// [END clean_basic_listen]
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}
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152+
@Override
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public void cleanBasicQuery() {
145154
// Clean up query listener
146155
// [START clean_basic_query]
147156
mMessagesQuery.removeEventListener(mMessagesQueryListener);
148157
// [END clean_basic_query]
149158
}
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@Override
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public void onStart() {
162+
super.onStart();
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basicListen();
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basicQuery();
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basicQueryValueListener();
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}
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@Override
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public void onStop() {
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super.onStop();
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cleanBasicListener();
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cleanBasicQuery();
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}
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}
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‎database/app/src/main/java/com/google/firebase/referencecode/database/interfaces/QueryActivityInterface.java‎

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package com.google.firebase.referencecode.database.interfaces;
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/**
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* Interface for {@link com.google.firebase.referencecode.database.QueryActivity}.
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*/
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public interface QueryActivityInterface {
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String getUid();
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void basicListen();
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void basicQuery();
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void basicQueryValueListener();
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void cleanBasicListener();
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void cleanBasicQuery();
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}

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