android - 全局变量在内部类中不为空,但在外部为空
问题描述
我有一个名为“myEmail”的全局变量,我想在方法内更改它的值,这样做时变量的值确实会改变,但仅在方法内(我已经使用日志检查过)但是在尝试再次使用变量时更改值后它为空。
我不知道这个问题的原因是什么。我尝试在 onCreate 上调用该方法,因为我认为变量 get 在更改值之前可能已被调用,但问题仍然存在。
这是我的代码
public class messagesFragment extends Fragment {
private FirebaseFirestore db = FirebaseFirestore.getInstance();
private String uid = FirebaseAuth.getInstance().getUid();
private CollectionReference messageRef = db.collection("messages");
private View v;
private RecyclerView recyclerView;
private messageAdapter mAdapter;
private String myEmail;
private FloatingActionButton addmsg;
public messagesFragment() {
}
// Creating the fragment view.
@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
v = inflater.inflate(R.layout.messages_fragment, container, false);
addmsg = (FloatingActionButton) v.findViewById(R.id.sendmsgfab);
addmsg.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent(getActivity(), createmessageActivity.class);
startActivity(intent);
}
});
getemail(); // Here the variable myEmail is null.
setupRecycler();
return v;
}
private void getemail(){
DocumentReference documentReference = db.collection("users").document(uid);
documentReference.get().addOnSuccessListener(new OnSuccessListener<DocumentSnapshot>() {
@Override
public void onSuccess(final DocumentSnapshot documentSnapshot) {
myEmail = documentSnapshot.get("email").toString();
// Here the variable myEmail is not null.
}
});
}
private void setupRecycler() {
Query query = messageRef.whereEqualTo("receiver", myEmail);
FirestoreRecyclerOptions<message> options = new FirestoreRecyclerOptions.Builder<message>()
.setQuery(query, message.class)
.build();
mAdapter = new messageAdapter(options);
recyclerView = (RecyclerView) v.findViewById(R.id.messagesRecycler);
recyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
recyclerView.setAdapter(mAdapter);
}
@Override
public void onStart() {
super.onStart();
mAdapter.startListening();
}
@Override
public void onStop() {
super.onStop();
mAdapter.stopListening();
}
}
解决方案
您的 getemail 方法的返回值是无效的!请在您的方法中将 String 替换为 void。