How to fetch data once and every time load from local - firebase

Question

I'm using Firebase3 in Ionic2 App. The requirement is to load data of approx 2000 objects and every time when page switched(using navigation) the data needs to be loaded. But loading every time data does not looks well.
So, is there any solution to fetch data once - like contacts list.
Then the loaded data will be displayed from local.
Thanks!

Answer 1

Try this code :-
private List<Contact> contactList;
private SharedPreferences shared ;
public View onCreateView(LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_contacts, container, false);
shared = getSharedPreferences("AppPref", MODE_PRIVATE);
//**Get the data from local storage**
List<Contacts> contactList = new Gson().fromJson((shared.getString("contacts", "")),new TypeToke<List<Contact>>(){}.getType());
if(contactList ==null) { // if no data found then call firebase service
contactList=new ArrayList();
//Use addListenerForSingleValueEvent instead of ValueEventListener.So this will listen only once.
mDataBaseRef.child("Your_Node").addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot postSnapshot : dataSnapshot.getChildren()){
contactList.add(postSnapshot.getValue(Contact.class);
}
//Save the data in Shared Preferences
SharedPreferences.Editor editor = shared.edit();
editor.putString("contacts", new Gson().toJson(contactList));
editor.commit();
}
#Override
public void onCancelled(FirebaseError firebaseError) {
contactList = null ;
}
});
}
return view ;
}