Android Firebase Wait For Data

in my android application I create an activity which contains a ListView which is populated with data from Firebase Database. The JSON Tree of the structure of the database is the

Solution 1:

You can use a simple counter to keep track of the number of pending loads:

companyRequests.addValueEventListener(newValueEventListener() {
    publicvoidonDataChange(DataSnapshot dataSnapshot) {
        // at the start we need to still load all childrenfinallong[] pendingLoadCount = { dataSnapshot.getChildrenCount() };
        for (DataSnapshot childSnapshot: dataSnapshot.getChildren()) {
            //For each key I retrieve its details from the requests nodeDatabaseReferencecurrRequest= rootNode.child("requests/" + childSnapshot.getKey());
            currRequest.addListenerForSingleValueEvent(newValueEventListener() {
                publicvoidonDataChange(DataSnapshot dataSnapshot) {
                    String time;
                    time = (String) dataSnapshot.child("time").getValue();
                    Requestrequest=newRequest(time);
                    allRequests.add(request);

                    // we loaded a child, check if we're done
                    pendingLoadCount[0] = pendingLoadCount[0] - 1;
                    if (pendingLoadCount[0] == 0) {
                        RequestAdapteradapter=newRequestAdapter(RequestsListActivity.this, allRequests);
                        rListView.setAdapter(adapter);
                    }
                }
                ...onCancelled...
            });
        }
    }
});

Solution 2:

I solved this using a java.util.concurrent.CountDownLatch:

In this example, replace EquityTotalListener with your implementation of ValueEventListener.

privatevoidrecalculate() {
        finalAtomicLongsumUpAll=newAtomicLong();
        finalCountDownLatchcnt=newCountDownLatch(mapUid2GeoLocation.keySet().size());
        for (final String uid : mapUid2GeoLocation.keySet()) {
            EquityTotalListenerel= mapUid2EquityListener.get(uid);
            if (el != null) {
                if (logger.isDebugEnabled()) {
                    logger.debug("Listener for " + uid + " already set up");
                    cnt.countDown();
                }
            } else {
                el = newEquityTotalListener(database.getDatabase(), uid) {

                    @OverridepublicvoidonCancelled(final DatabaseError databaseError) {
                        super.onCancelled(databaseError);
                        cnt.countDown();
                    }

                    @OverrideprotectedvoidvalueChanged(final String key, final Object value) {
                        if (value != null) {
                            sumUpAll.getAndAdd(Long.parseLong(value.toString()));
                            cnt.countDown();
                        }
                    };
                }.attach();
                mapUid2EquityListener.put(uid, el);
            }
        }
        if (logger.isDebugEnabled()) {
            logger.debug("Waitung for countdown..");
        }
        try {
            finalbooleanallGood= cnt.await(10, TimeUnit.SECONDS);
            if (allGood) {
                if (logger.isDebugEnabled()) {
                    logger.debug("Done waiting, " + uid + " owns " + sumUpAll.get() + " equity");
                }
            } else {
                if (logger.isWarnEnabled()) {
                    logger.warn("Waiting for read operations ran into timeout");
                }
            }
        } catch (final InterruptedException e) {
            if (logger.isErrorEnabled()) {
                logger.error(e.getLocalizedMessage(), e);
            }
        }

    }