/
OfflineActivity.java
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/
OfflineActivity.java
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package com.google.firebase.referencecode.database;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
import android.util.Log;
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.FirebaseDatabase;
import com.google.firebase.database.OnDisconnect;
import com.google.firebase.database.ServerValue;
import com.google.firebase.database.ValueEventListener;
public class OfflineActivity extends AppCompatActivity {
private static final String TAG = "OfflineActivity";
private void enablePersistence() {
// [START rtdb_enable_persistence]
FirebaseDatabase.getInstance().setPersistenceEnabled(true);
// [END rtdb_enable_persistence]
}
private void keepSynced() {
// [START rtdb_keep_synced]
DatabaseReference scoresRef = FirebaseDatabase.getInstance().getReference("scores");
scoresRef.keepSynced(true);
// [END rtdb_keep_synced]
// [START rtdb_undo_keep_synced]
scoresRef.keepSynced(false);
// [END rtdb_undo_keep_synced]
}
private void queryRecentScores() {
// [START rtdb_query_recent_scores]
DatabaseReference scoresRef = FirebaseDatabase.getInstance().getReference("scores");
scoresRef.orderByValue().limitToLast(4).addChildEventListener(new ChildEventListener() {
@Override
public void onChildAdded(@NonNull DataSnapshot snapshot, String previousChild) {
Log.d(TAG, "The " + snapshot.getKey() + " dinosaur's score is " + snapshot.getValue());
}
// [START_EXCLUDE]
@Override
public void onChildRemoved(@NonNull DataSnapshot dataSnapshot) {}
@Override
public void onChildMoved(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {}
@Override
public void onChildChanged(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {}
// [END_EXCLUDE]
});
// [END rtdb_query_recent_scores]
// [START rtdb_query_recent_scores_overlap]
scoresRef.orderByValue().limitToLast(2).addChildEventListener(new ChildEventListener() {
@Override
public void onChildAdded(@NonNull DataSnapshot snapshot, String previousChild) {
Log.d(TAG, "The " + snapshot.getKey() + " dinosaur's score is " + snapshot.getValue());
}
// [START_EXCLUDE]
@Override
public void onChildRemoved(@NonNull DataSnapshot dataSnapshot) {}
@Override
public void onChildMoved(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {}
@Override
public void onChildChanged(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {}
// [END_EXCLUDE]
});
// [END rtdb_query_recent_scores_overlap]
}
private void onDisconnect() {
// [START rtdb_on_disconnect_set]
DatabaseReference presenceRef = FirebaseDatabase.getInstance().getReference("disconnectmessage");
// Write a string when this client loses connection
presenceRef.onDisconnect().setValue("I disconnected!");
// [END rtdb_on_disconnect_set]
// [START rtdb_on_disconnect_remove]
presenceRef.onDisconnect().removeValue(new DatabaseReference.CompletionListener() {
@Override
public void onComplete(DatabaseError error, @NonNull DatabaseReference reference) {
if (error != null) {
Log.d(TAG, "could not establish onDisconnect event:" + error.getMessage());
}
}
});
// [END rtdb_on_disconnect_remove]
// [START rtdb_on_disconnect_cancel]
OnDisconnect onDisconnectRef = presenceRef.onDisconnect();
onDisconnectRef.setValue("I disconnected");
// ...
// some time later when we change our minds
// ...
onDisconnectRef.cancel();
// [END rtdb_on_disconnect_cancel]
}
private void getConnectionState() {
// [START rtdb_listen_connected]
DatabaseReference connectedRef = FirebaseDatabase.getInstance().getReference(".info/connected");
connectedRef.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot snapshot) {
boolean connected = snapshot.getValue(Boolean.class);
if (connected) {
Log.d(TAG, "connected");
} else {
Log.d(TAG, "not connected");
}
}
@Override
public void onCancelled(@NonNull DatabaseError error) {
Log.w(TAG, "Listener was cancelled");
}
});
// [END rtdb_listen_connected]
}
private void disconnectionTimestamp() {
// [START rtdb_on_disconnect_timestamp]
DatabaseReference userLastOnlineRef = FirebaseDatabase.getInstance().getReference("users/joe/lastOnline");
userLastOnlineRef.onDisconnect().setValue(ServerValue.TIMESTAMP);
// [END rtdb_on_disconnect_timestamp]
}
private void getServerTimeOffset() {
// [START rtdb_server_time_offset]
DatabaseReference offsetRef = FirebaseDatabase.getInstance().getReference(".info/serverTimeOffset");
offsetRef.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot snapshot) {
double offset = snapshot.getValue(Double.class);
double estimatedServerTimeMs = System.currentTimeMillis() + offset;
}
@Override
public void onCancelled(@NonNull DatabaseError error) {
Log.w(TAG, "Listener was cancelled");
}
});
// [END rtdb_server_time_offset]
}
private void fullConnectionExample() {
// [START rtdb_full_connection_example]
// Since I can connect from multiple devices, we store each connection instance separately
// any time that connectionsRef's value is null (i.e. has no children) I am offline
final FirebaseDatabase database = FirebaseDatabase.getInstance();
final DatabaseReference myConnectionsRef = database.getReference("users/joe/connections");
// Stores the timestamp of my last disconnect (the last time I was seen online)
final DatabaseReference lastOnlineRef = database.getReference("/users/joe/lastOnline");
final DatabaseReference connectedRef = database.getReference(".info/connected");
connectedRef.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot snapshot) {
boolean connected = snapshot.getValue(Boolean.class);
if (connected) {
DatabaseReference con = myConnectionsRef.push();
// When this device disconnects, remove it
con.onDisconnect().removeValue();
// When I disconnect, update the last time I was seen online
lastOnlineRef.onDisconnect().setValue(ServerValue.TIMESTAMP);
// Add this device to my connections list
// this value could contain info about the device or a timestamp too
con.setValue(Boolean.TRUE);
}
}
@Override
public void onCancelled(@NonNull DatabaseError error) {
Log.w(TAG, "Listener was cancelled at .info/connected");
}
});
// [END rtdb_full_connection_example]
}
}