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我是通用的firebase數據庫和firebase的新手，在嘗試使用它時遇到了一些小問題。DataSnapshot.getValue（）不能正確檢索對象
我使用下面的JSON代碼我從火力控制檯進口的，原來我剛剛創建的火力控制檯數據庫結構，那麼下載的JSON代碼，並如下：
{
"rides" : {
"arrive" : "kech",
"depart" : "agadir",
"detail" : "0,1",
"msg" : false,
"phone" : true,
"price" : 15,
"profile_id" : 0,
"spots" : 3,
"timedate" : "11/12/2017 11:15",
"vocal_id" : 0
}
}
對象我想取回被命名爲Ride.java：
public class Ride {
private String arrive;
private String depart;
private String detail;
private boolean msg;
private boolean phone;
private int price;
private int profile_id;
private int spots;
private String timedate;
private int vocal_id;
public Ride() {}
// public getters (I created them I just didn't post it all to make the post shorter)
}
聽我的數據庫引用我使用下面的代碼：
FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference ref = database.getReference("rides").child("0"); // 0 is the ride id
ref.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot singleSnapshot : dataSnapshot.getChildren()){
Ride ride = singleSnapshot.getValue(Ride.class);
rides.add(ride); // list of rides used later in a listadapter
}
}
@Override
public void onCancelled(DatabaseError databaseError) {
Log.e(TAG, "onCancelled", databaseError.toException());
}
});
我試圖從firebase數據庫獲取一個單騎，並在我的應用程序中顯示它。在firebase控制檯它有網址：https://myapp.firebaseio.com/rides/0（第二騎有ID 1等）。抓住所有遊樂設施的最佳做法是什麼？從每個遊樂設施獲取其屬性是什麼？
編輯：當我刪除.child("0")我沒有得到任何錯誤，但沒有出現在我的ListView 。顯然rides.add(ride)不會出於某種原因。
我加入的一個簡單的實例騎的addListenerForSingleValueEvent()方法外測試它，它工作正常。
我也試過改變聽者addValueEventListener()，相同的結果..
EDIT2：我得到一個錯誤信息，當我嘗試從我的數據庫中檢索的整數。
我在我的數據庫監聽嘗試這樣做：
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot singleSnapshot: dataSnapshot.getChildren()) {
int price = (int) singleSnapshot.child("price").getValue(); // error takes place here
Log.d("FirebaseDb", String.valueOf(price));
}
}
結果是這樣的錯誤：（所有整數）
java.lang.ClassCastException: java.lang.Long cannot be cast to java.lang.Integer
at com.ride.ive.anas.iveride.Fragments.RidesFragment$1.onDataChange(RidesFragment.java:96)
但是，當我取回一個字符串或布爾它工作正常，如：
String arrive = (String) singleSnapshot.child("arrive").getValue();
或者Boolean usePhone = (Boolean) singleSnapshot.child("phone").getValue();
EDIT3：這裏是經@Prodigy請求RidesFragment.java文件。 其中我有一個ListView，我嘗試顯示存儲在我的firebase數據庫中的所有乘車實例。
public class RidesFragment extends Fragment {
ListView list;
RidesAdapter2 ridesAdapter;
List<Ride> rides;
Ride ride;
List<RidePojo> filteredRides;
LinearLayout layoutFilter;
boolean filtersVisible = false;
boolean searchDone = false;
String userNumber;
public RidesFragment() {
// Required empty public constructor
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_rides, container, false);
getActivity().setTitle("Search for a ride:");
// filter action button stuff
setHasOptionsMenu(true);
layoutFilter = rootView.findViewById(R.id.ll_filter_screen);
/*FragmentManager fm = getActivity().getSupportFragmentManager();
fm.popBackStack(null, FragmentManager.POP_BACK_STACK_INCLUSIVE);*/
ridesAdapter = new RidesAdapter2(getContext(), rides);
Bundle arguments = getArguments();
list = rootView.findViewById(R.id.rides_list);
rides = new ArrayList<>();
FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference ref = database.getReference("rides");
ref.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot singleSnapshot: dataSnapshot.getChildren()) {
Ride ride = singleSnapshot.getValue(Ride.class);
rides.add(ride);
ridesAdapter.notifyDataSetChanged();
Log.d("FbDatabase", singleSnapshot.toString());
}
}
@Override
public void onCancelled(DatabaseError databaseError) {
Log.e(TAG, "onCancelled", databaseError.toException());
}
});
rides.add(ride);
// In case the rides ArrayList is not empty another fragment appears for no rides criteria
if(rides.isEmpty()) {
rootView = inflater.inflate(R.layout.fragment_empty, container, false);
Button rideButton = rootView.findViewById(R.id.btn_post_ride);
Button requestButton = rootView.findViewById(R.id.btn_post_request);
rideButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
launchFragment(new OfferRideFragment(), getActivity());
}
});
requestButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
launchFragment(new RequestFragment(), getActivity());
}
});
}
else {
list.setAdapter(ridesAdapter);
}
return rootView;
}
protected void launchFragment(Fragment f, FragmentActivity a) {
android.support.v4.app.FragmentTransaction fragmentTransaction =
a.getSupportFragmentManager().beginTransaction();
fragmentTransaction.replace(R.id.fragment_container, f);
fragmentTransaction.commit();
}
// ....
}
創建getter和爲你的旅程類的東西其餘制定者編輯的代碼可以從這個stackoverflower答案[這裏]（https://stackoverflow.com/questions/30933328/how遵循-to-convert-firebase-data-to-java-object） –
我創建了它們，我只是不想將它們寫在這裏以使文章更短 – Anas
將代碼添加到數據庫引用的監聽器的代碼 –