Android 用户列表为空
我想使用Firebase实时数据库创建一个聊天应用程序，其中包含一个RecyclerView和一个CardView，每个用户都有自己的名字。问题是，只有当数据库中有3个人时，才会显示CardView。 我在此链接中附上了我的数据库图片： 用户片段：Android 用户列表为空,android,firebase,firebase-realtime-database,Android,Firebase,Firebase Realtime Database,我想使用Firebase实时数据库创建一个聊天应用程序，其中包含一个RecyclerView和一个CardView，每个用户都有自己的名字。问题是，只有当数据库中有3个人时，才会显示CardView。 我在此链接中附上了我的数据库图片： 用户片段： public class UsersFragment extends Fragment { private RecyclerView recyclerView; private UserAdapter userAdapter;
public class UsersFragment extends Fragment {
private RecyclerView recyclerView;
private UserAdapter userAdapter;
private List<User> mUsers;
@Override
public View onCreateView (LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View view= inflater.inflate ( R.layout.fragment_users3, container, false );
recyclerView=view.findViewById (R.id.recycler_view );
recyclerView.setLayoutManager ( new LinearLayoutManager ( getContext () ) );
mUsers=new ArrayList<> ( );
readUsers();
return view;
}
private void readUsers () {
final FirebaseUser firebaseUser= FirebaseAuth.getInstance ().getCurrentUser ();
DatabaseReference referenc= FirebaseDatabase.getInstance ().getReference ("users");
referenc.addValueEventListener ( new ValueEventListener () {
@Override
public void onDataChange (@NonNull DataSnapshot dataSnapshot) {
mUsers.clear ();
for(DataSnapshot snapshot:dataSnapshot.getChildren ()){
User user=snapshot.getValue (User.class);
assert user!=null;
assert firebaseUser!=null;
if(!firebaseUser.getUid ().equals ( user.getUid () )){
mUsers.add ( user );
}
}
userAdapter=new UserAdapter ( getContext (),mUsers );
recyclerView.setAdapter ( userAdapter );
}
@Override
public void onCancelled (@NonNull DatabaseError databaseError) {
}
} );
}
}
public class UsersActivity extends AppCompatActivity {
@Override
protected void onCreate (Bundle savedInstanceState) {
super.onCreate ( savedInstanceState );
setContentView ( R.layout.activity_users );
TabLayout tablayout=findViewById ( R.id.tab_layout );
ViewPager viewPager=findViewById ( R.id.view_pager );
ViewPagerAdapter viewPagerAdapter=new ViewPagerAdapter ( getSupportFragmentManager () );
viewPagerAdapter.addFragment ( new ChatFragment (),"Chats" ); // `new ChatFragment()` should be inside `FragmentPagerAdapter.getItem()`
viewPagerAdapter.addFragment ( new UsersFragment (),"Users" ); // `new UsersFragment()` should be inside `FragmentPagerAdapter.getItem()`
viewPager.setAdapter (viewPagerAdapter );
tablayout.setupWithViewPager (viewPager );
}
class ViewPagerAdapter extends FragmentPagerAdapter{
private ArrayList<Fragment> fragments; // this line can cause crashes
private ArrayList<String> titles;
ViewPagerAdapter(FragmentManager fn){
super(fn);
this.fragments=new ArrayList<> ( );
this.titles=new ArrayList<> ( );
}
@NonNull
@Override
public Fragment getItem (int position) {
return fragments.get ( position );
}
@Override
public int getCount () {
return fragments.size ();
}
public void addFragment(Fragment fragment,String title){
fragments.add ( fragment ); // this line can cause crashes
titles.add ( title );
}
@Nullable
@Override
public CharSequence getPageTitle (int position) {
return titles.get ( position );
}
}
}
我希望显示数据库中的所有用户。将firebase数据库中的键更改为firstName、secondName、email，而不是firstName、secondName和电子邮件。如果在模型类中找不到正确的键及其getter和setter，则无法映射firebase中的数据。将firebase数据库中的键更改为firstName、secondName、email，而不是firstName、secondName和E-mail。如果在模型类中找不到正确的键及其getter和setter，则无法映射firebase中的数据。数据库中的JSON中有属性
FirstNameUsergetFirstName（）firstName{
"users": {
"uid1": {
"email": "...",
"firstName": "...",
"secondName": "..."
}
}
}
PropertyNamepublic class User {
private String firstName;
private String secondName;
private String uid;
private String email;
public User(){
}
public User (String firstName, String secondName, String uid, String email) {
this.firstName = firstName;
this.secondName = secondName;
this.uid=uid;
this.email=email;
}
public User (String firstname, String secondname) {
}
@PropertyName("FirstName")
public String getFirstName () {
return firstName;
}
@PropertyName("SecondName")
public String getSecondName () {
return secondName;
}
@PropertyName("Uid")
public String getUid () {
return uid;
}
@PropertyName("E-mail")
public String getEmail () {
return email;
}
@PropertyName("FirstName")
public void setFirstName (String firstName) {
this.firstName = firstName;
}
@PropertyName("SecondName")
public void setSecondName (String secondName) {
this.secondName = secondName;
}
@PropertyName("Uid")
public void setUid (String uid) {
this.uid = uid;
}
@PropertyName("E-mail")
public void setEmail (String email) {
this.email = email;
}
}
也可以在这里看到我的答案：在数据库的JSON中有一个属性
FirstNameUsergetFirstName（）firstName{
"users": {
"uid1": {
"email": "...",
"firstName": "...",
"secondName": "..."
}
}
}
PropertyNamepublic class User {
private String firstName;
private String secondName;
private String uid;
private String email;
public User(){
}
public User (String firstName, String secondName, String uid, String email) {
this.firstName = firstName;
this.secondName = secondName;
this.uid=uid;
this.email=email;
}
public User (String firstname, String secondname) {
}
@PropertyName("FirstName")
public String getFirstName () {
return firstName;
}
@PropertyName("SecondName")
public String getSecondName () {
return secondName;
}
@PropertyName("Uid")
public String getUid () {
return uid;
}
@PropertyName("E-mail")
public String getEmail () {
return email;
}
@PropertyName("FirstName")
public void setFirstName (String firstName) {
this.firstName = firstName;
}
@PropertyName("SecondName")
public void setSecondName (String secondName) {
this.secondName = secondName;
}
@PropertyName("Uid")
public void setUid (String uid) {
this.uid = uid;
}
@PropertyName("E-mail")
public void setEmail (String email) {
this.email = email;
}
}
也可以在这里看到我的答案：我按照你告诉我的做了，在调试器中它显示了“com.example.sportsbuddy.Fragments.UsersFragment$1.onDataChange（UsersFragment.java:60）”和我的应用程序崩溃。我能做什么？如果你的应用程序崩溃，找到完整的错误消息和堆栈跟踪，并将它们添加到这里或你的问题中（因为你可以将它们格式化以使其更具可读性）。顺便说一句：我给了你两个解决问题的选项。知道你使用这两个选项中的哪一个可能会有所帮助。我还在你的另一篇文章中更新了我对这个问题的答案。我按照你告诉我的做了，并在调试器中显示了我“在com.example.sportsbuddy.Fragments.UsersFragment$1.onDataChange（UsersFragment.java:60）”和我的应用程序崩溃。我能做什么？如果你的应用程序崩溃，找到完整的错误消息和堆栈跟踪，并将它们添加到这里，或者添加到你的问题中（因为你可以在那里对它们进行格式化以使其更具可读性）顺便说一句：我给了你两个解决问题的方法。知道你用哪一个可能会有帮助。我还在你的另一篇文章中更新了我对这个问题的回答。
public class User {
private String firstName;
private String secondName;
private String uid;
private String email;
public User(){
}
public User (String firstName, String secondName, String uid, String email) {
this.firstName = firstName;
this.secondName = secondName;
this.uid=uid;
this.email=email;
}
public User (String firstname, String secondname) {
}
@PropertyName("FirstName")
public String getFirstName () {
return firstName;
}
@PropertyName("SecondName")
public String getSecondName () {
return secondName;
}
@PropertyName("Uid")
public String getUid () {
return uid;
}
@PropertyName("E-mail")
public String getEmail () {
return email;
}
@PropertyName("FirstName")
public void setFirstName (String firstName) {
this.firstName = firstName;
}
@PropertyName("SecondName")
public void setSecondName (String secondName) {
this.secondName = secondName;
}
@PropertyName("Uid")
public void setUid (String uid) {
this.uid = uid;
}
@PropertyName("E-mail")
public void setEmail (String email) {
this.email = email;
}
}