如何解决来自 Firebase 的 ExpandableListView，取决于更改的数据
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标签“ViewFragment.java”： 在这里，您可以看到一个 GoogleMap，其中 UUID 和经度/纬度存储在来自不同用户的 Realtime firebase 中。此处存储 currentLocation。这意味着一旦用户移动，firebase 就会自动更新并覆盖旧的位置值。
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标签“PositionFragment.java”： 这里应该可以看到一个 ExpandedListView。这里查询来自 Firebase 的用户。它们应该在 ExpandedListView 中可见。如果您展开它，相应用户的经度也应该出现。
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标签 不相关
firebase 中的值根据 currentLocation（我的另一个类）而变化，但 ListSize 是相同的。计数器继续计数。这里它超过了 listColleagues.get(counter) 中的列表大小。所以我加了一个if条件，但是出现异常
我的问题是我的 readFromFirebase() 方法有问题：
这个异常发生在 longitude =data.child("location").child("longitude").getValue().toString();
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference
at com.example.thesis.PositionFragment$1.onDataChange(PositionFragment.java:75)
at com.google.firebase.database.core.ValueEventRegistration.fireEvent(ValueEventRegistration.java:75)
at com.google.firebase.database.core.view.DataEvent.fire(DataEvent.java:63)
at com.google.firebase.database.core.view.EventRaiser$1.run(EventRaiser.java:55)
at android.os.Handler.handleCallback(Handler.java:938)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:223)
at android.app.ActivityThread.main(ActivityThread.java:7656)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
public class PositionFragment extends Fragment {
private static final String TAG = "PositionFragment";
private ExpandableListView expandableListView;
private Colleaguelistadapter colleaguelistadapter;
private DatabaseReference databaseReference;
private List<String> listColleagues = new ArrayList<>();
private HashMap<String,List<String>> listColleaguesDetails = new HashMap<>();
public PositionFragment() {
// required empty public constructor
}
@Override
public View onCreateView(LayoutInflater inflater,ViewGroup container,Bundle savedInstanceState) {
// View initialisieren
View rootView = inflater.inflate(R.layout.fragment_tab_position,container,false);
//Initialisieren und variable zuweisen
expandableListView = (ExpandableListView) rootView.findViewById(R.id.list_view_position_tab);
colleaguelistadapter = new Colleaguelistadapter(listColleagues,listColleaguesDetails);
expandableListView.setAdapter(colleaguelistadapter);
readFromFirebase();
return rootView;
}
public void readFromFirebase() {
databaseReference = FirebaseDatabase.getInstance().getReference();
databaseReference.child("user").addValueEventListener(new ValueEventListener() {
List<String> childItem;
int counter = 0;
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
childItem = new ArrayList<>();
String longitude;
for (DataSnapshot data : dataSnapshot.getChildren()) {
// As long and lat change,he starts the list over
//again. Here the counter counts further and sets
//the index higher,although the size is already reached.
//unique ID from every user and details
String colleagueID = data.getKey();
longitude = data.child("location").child("longitude").getValue().toString();
listColleagues.add(colleagueID);
childItem.add(longitude);
//if counter is greater than size (when location is changed,but the
// number of users is same,then replace this user with the new values
if (listColleagues.size()<= counter && listColleagues.size() != 0) {
int index = listColleagues.indexOf(colleagueID);
listColleaguesDetails.put(listColleagues.set(index,colleagueID),childItem);
Log.d(TAG,"counter greater than size" + "Counter: " + counter +" --- Size: " + listColleagues.size());
}else {
listColleaguesDetails.put(listColleagues.get(counter),Collections.singletonList(childItem.get(counter)));
counter++;
}
}
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});
// [END read_message]
}
public class Colleaguelistadapter extends Baseexpandablelistadapter {
final LayoutInflater inf;
List<String> listColleagues;
HashMap<String,List<String>> listColleaguesDetails;
public Colleaguelistadapter(List<String> listColl,HashMap<String,List<String>> listCollDtls) {
this.listColleagues = listColl;
this.listColleaguesDetails = listCollDtls;
inf = LayoutInflater.from(getActivity());
}
@Override
public int getGroupCount() {
//return listColleagues.size();
return 0;
}
@Override
public int getChildrenCount(int groupPosition) {
return this.listColleaguesDetails.get(this.listColleagues.get(groupPosition)).size();
}
@Override
public Object getGroup(int groupPosition) {
return this.listColleagues.get(groupPosition);
}
@Override
public Object getChild(int groupPosition,int childPosition) {
return this.listColleaguesDetails.get(this.listColleagues.get(groupPosition)).get(childPosition);
}
@Override
public long getGroupId(int groupPosition) {
return groupPosition;
}
@Override
public long getChildId(int groupPosition,int childPosition) {
return childPosition;
}
@Override
public boolean hasstableIds() {
return false;
}
@Override
public View getGroupView(int groupPosition,boolean isExpanded,View convertView,ViewGroup parent) {
String group = (String) getGroup(groupPosition);
if (convertView == null) {
//LayoutInflater layoutInflater = (LayoutInflater) this.fragment.getActivity().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
//convertView = layoutInflater.inflate(R.layout.list_group,null);
convertView = inf.inflate(R.layout.list_group,null);
}
TextView textView = convertView.findViewById(R.id.list_parent);
textView.setText(group);
return convertView;
}
@Override
public View getChildView(int groupPosition,int childPosition,boolean isLastChild,ViewGroup parent) {
String child = (String) getChild(groupPosition,childPosition);
if (convertView == null) {
//LayoutInflater layoutInflater = (LayoutInflater) this.fragment.getActivity().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
// convertView = layoutInflater.inflate(R.layout.list_item,null);
}
TextView textView = convertView.findViewById(R.id.list_child);
textView.setText(child);
return convertView;
}
@Override
public boolean isChildSelectable(int groupPosition,int childPosition) {
return true;
}
}
}
firebase structure 有人能帮我改一下吗？
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