I am developing my first Android app using Firebase and I love it. My question is, how should I go about fetching data from the Firebase database properly? I am a bit confused about fetching data once and then with that data fetch some more.
I am basically nesting 'OnCompleteListeners' one inside of another and this pattern disturbs me. Is there a better and more proper way?
Here is my current approach:
//This is a weather app, users can monitor different weather stations
//We first get the weather stations that the current user owns:
// I used two collections in this approach, "ownership" permission is read only to the user
DocumentReference docRef = mDatabase.collection("ownership").document( mUser.getUid() );
docRef.get().addOnCompleteListener( new OnCompleteListener<DocumentSnapshot>() {
@Override
public void onComplete(@NonNull Task<DocumentSnapshot> task) {
if ( task.isSuccessful() ) {
DocumentSnapshot document = task.getResult();
if ( document.exists() ) {
Map<String, Object> data = document.getData();
if ( data != null && data.containsKey("stations") ) {
// data is an string array, here is my ugly solution:
stationIds = data.get("stations").toString().replaceAll("[\\[\\]]", "").split(",");
if ( stationIds.length != 0 ) {
for ( int i = 0; i < stationIds.length; i++ ) {
// Now that I have the stations IDs I can get its data:
// !! the collection "stations" have read and write permission
// THIS PATTERN SEEMS VERY REDUNDANT!
DocumentReference docRef = mDatabase.collection("stations").document(stationIds[i]);
docRef.get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
@Override
public void onComplete(@NonNull Task<DocumentSnapshot> task) {
if (task.isSuccessful()) {
DocumentSnapshot document = task.getResult();
if (document.exists()) {
Map<String, Object> data = document.getData();
Log.d(TAG, "Document Snapshot: " + document.getData());
if ( data != null && data.containsKey("name") ) {
LinearLayout ll_root = MainActivity.this.findViewById(R.id.ll_station_list);
LinearLayout ll_new = new LinearLayout(MainActivity.this);
ll_new.setLayoutParams(new LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, LinearLayout.LayoutParams.WRAP_CONTENT));
ll_new.setPadding(20,50,20,20);
TextView tv_station_title = new TextView(MainActivity.this);
tv_station_title.setText(data.get("name").toString());
ll_new.addView( tv_station_title);
ll_root.addView( ll_new );
ll_new.setOnClickListener( new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this, LiveStation.class);
startActivity(intent);
}
});
}
} else {
Log.w(TAG, "Station not found");
}
} else {
Log.w(TAG, "Unable to get station");
}
}
});
}
}
}
Log.d( TAG, "Document Snapshot: " + document.getData() );
} else {
Log.w(TAG, "No document found");
}
} else {
Log.w(TAG, "Get user stations failed: " + task.getException() );
}
}
});
I am not very familiar with async calls in Android. Usually I create a model that talks to the database and it can be called from anywhere in the app structure, but using Firebase it seems that I can't do that. It seems that every view requires its own unique calls to the database. Or maybe I got the whole idea wrong.
