[英]How to update firebase realtime database automatically at a certain time daily in android?
[英]How to constantly update query for Firebase Realtime Database with LiveData and ViewModel in Android
我在 Android 中使用 Firebase 实时数据库和 LiveData 和 ViewModel,我想不断更新查询。
这是 ViewModel 类:
public class ViewModel_MainActivity extends ViewModel {
/*
LiveData with Database query for the Firebase node "Ratings"
*/
private static long currentTimeMillisRating = System.currentTimeMillis();
private static double pastMinuteForDisplayingRatings = 1;
private static long pastTimeMillisRatings = System.currentTimeMillis() - (long) (pastMinuteForDisplayingRatings * 60 * 60 * 1000);
private static final Query QUERY_RATINGS =
FirebaseDatabase.getInstance(DB_SQLite_Firebase_Entries.FIREBASE_URL).getReference().child(DB_SQLite_Firebase_Entries.FIREBASE_NODE_RATINGS).orderByChild(DB_SQLite_Firebase_Entries.FIREBASE_RATINGDATEINMILLISECONDS).endAt(pastTimeMillisRatings);
private final LiveData_FirebaseRating liveData_firebaseRating = new LiveData_FirebaseRating(QUERY_RATINGS);
@NonNull
public LiveData_FirebaseRating getDataSnapshotLiveData_FirebaseRating() {
Log.e("LogTag_ViMo", "pastTimeMillisRatings: " + pastTimeMillisRatings);
return liveData_firebaseRating;
}
}
这是 LiveData 类:
public class LiveData_FirebaseRating extends LiveData<DataSnapshot> {
private static final String LOG_TAG = "LiveData_FirebaseRating";
private Query query;
private final LiveData_FirebaseRating.MyValueEventListener listener = new LiveData_FirebaseRating.MyValueEventListener();
DataSnapshot currentDataSnapShotFromFirebase;
public LiveData_FirebaseRating(Query query) {
this.query = query;
}
public LiveData_FirebaseRating(DatabaseReference ref) {
this.query = ref;
}
public void changeQuery(Query newQuery) {
this.query = newQuery;
}
public DataSnapshot getCurrentDataSnapShotFromFirebase() {
return currentDataSnapShotFromFirebase;
}
public void setCurrentDataSnapShotFromFirebase(DataSnapshot currentDataSnapShotFromFirebase) {
this.currentDataSnapShotFromFirebase = currentDataSnapShotFromFirebase;
}
@Override
protected void onActive() {
Log.d(LOG_TAG, "onActive");
query.addValueEventListener(listener);
}
@Override
protected void onInactive() {
Log.d(LOG_TAG, "onInactive");
query.removeEventListener(listener);
}
private class MyValueEventListener implements ValueEventListener {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
setValue(dataSnapshot);
}
@Override
public void onCancelled(DatabaseError databaseError) {
Log.e(LOG_TAG, "Can't listen to query " + query, databaseError.toException());
}
}
}
这是主要活动的一部分,其中创建和观察实时数据和视图模型:
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
binding = ActivityMainBinding.inflate(getLayoutInflater());
View view = binding.getRoot();
setContentView(view);
/*
Initiate View Model with LiveData for Firebase
*/
rootRef_Firebase = FirebaseDatabase.getInstance(DB_SQLite_Firebase_Entries.FIREBASE_URL).getReference();
viewModel = new ViewModelProvider(this).get(ViewModel_MainActivity.class);
liveData_firebaseRating = viewModel.getDataSnapshotLiveData_FirebaseRating();
liveData_firebaseRating.observe(this, new Observer<DataSnapshot>() {
@Override
public void onChanged(@Nullable DataSnapshot dataSnapshot) {
liveData_firebaseRating.setCurrentDataSnapShotFromFirebase(dataSnapshot);
if(liveData_firebaseRating.getCurrentDataSnapShotFromFirebase()!=null) {
//Do something with the dataSnapshot of the query
}
}// end onChange
}); //end observe
}
所以我的问题在于ViewModel_MainActivity
类中的QUERY_RATINGS
没有更新。 我想要的是从FIREBASE_NODE_RATINGS
返回所有节点,其 at 属性FIREBASE_RATINGDATEINMILLISECONDS
早于 1 分钟(这意味着该条目是在当前时隙之前至少 1 分钟创建的)。 我怎样才能做到这一点,以便我总是得到这些节点?
Firebase Query
对象是不可变的,它们的参数是固定值。 所以没有办法更新现有的查询,也没有自动更新的“一分钟前”值。
我能很快想到的选项:
startAt
和endAt
)并将它们与您已有的结果合并。根据我所知道的,我可能会从第三种选择开始,因为它似乎是最简单的。
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