错误：java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法"boolean java.lang.String.equals(java.lang.Object)"

Question

请帮忙，我真的不知道这是怎么发生的，我的应用程序运行良好，然后安卓工作室更新了一个dependencie，然后发生了这种情况，我试着把一切都放原样，但仍然没有，请帮忙。下面的活动不是应用程序打开时显示的主活动，而是用户验证后显示的活动。

Process: com.Interactive.textmefriends, PID: 7638
java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.equals(java.lang.Object)' on a null object reference
at com.Interactive.textmefriends.Fragments.UsersFragment$3.onDataChange(UsersFragment.java:126)
at com.google.firebase.database.core.ValueEventRegistration.fireEvent(com.google.firebase:firebase-database@@19.2.1:75)
at com.google.firebase.database.core.view.DataEvent.fire(com.google.firebase:firebase-database@@19.2.1:63)
at com.google.firebase.database.core.view.EventRaiser$1.run(com.google.firebase:firebase-database@@19.2.1:55)
at android.os.Handler.handleCallback(Handler.java:883)
at android.os.Handler.dispatchMessage(Handler.java:100)
at android.os.Looper.loop(Looper.java:214)
at android.app.ActivityThread.main(ActivityThread.java:7356)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)

活动

package com.Interactive.textmefriends;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentPagerAdapter;
import androidx.viewpager.widget.ViewPager;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.TextView;
import com.Interactive.textmefriends.Fragments.ChatsFragment;
import com.Interactive.textmefriends.Fragments.ProfileFragment;
import com.Interactive.textmefriends.Fragments.UsersFragment;
import com.Interactive.textmefriends.Model.Chat;
import com.Interactive.textmefriends.Model.User;
import com.bumptech.glide.Glide;
import com.google.android.gms.ads.AdRequest;
import com.google.android.gms.ads.AdView;
import com.google.android.gms.ads.MobileAds;
import com.google.android.material.tabs.TabLayout;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;
import java.util.ArrayList;
import java.util.HashMap;
import de.hdodenhof.circleimageview.CircleImageView;
public class Main2Activity extends AppCompatActivity {
CircleImageView profile_image;
TextView username;
FirebaseUser firebaseUser;
DatabaseReference reference;
private AdView mAdView;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main2);
MobileAds.initialize(this, "ca-app-pub-8087632256608585~2089051412");
mAdView = findViewById(R.id.adView);
AdRequest adRequest = new AdRequest.Builder().build();
mAdView.loadAd(adRequest);

Toolbar toolbar = findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
getSupportActionBar().setTitle("");
profile_image = findViewById(R.id.profile_image);
username = findViewById(R.id.username);
firebaseUser = FirebaseAuth.getInstance().getCurrentUser();
reference = FirebaseDatabase.getInstance().getReference("Users").child(firebaseUser.getUid());

reference.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
User user = dataSnapshot.getValue(User.class);
username.setText(user.getUsername());
if (user.getImageURL().equals("default"))  {
profile_image.setImageResource(R.mipmap.ic_launcher);
}
else {
Glide.with(getApplicationContext()).load(user.getImageURL()).into(profile_image);
}
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});

final TabLayout tabLayout = findViewById(R.id.tab_layout);
final ViewPager viewPager = findViewById(R.id.view_pager);
reference = FirebaseDatabase.getInstance().getReference("Chats");
reference.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
ViewPagerAdapter viewPagerAdapter = new ViewPagerAdapter(getSupportFragmentManager());
int unread = 0;
for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
Chat chat =  snapshot.getValue(Chat.class);
if (chat.getReceiver().equals(firebaseUser.getUid()) && !chat.isIsseen()) {
unread++;
}
}
if (unread == 0) {
viewPagerAdapter.addFragment(new ChatsFragment(), "Chats");
}
else {
viewPagerAdapter.addFragment(new ChatsFragment(), "("+unread+") Chats");
}
viewPagerAdapter.addFragment(new UsersFragment(), "Users");  //setTitle(R.string.fragment_users_title)
viewPagerAdapter.addFragment(new ProfileFragment(), "Profile");  //setTitle(R.string.fragment_profile_title)
viewPager.setAdapter(viewPagerAdapter);
tabLayout.setupWithViewPager(viewPager);
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.menu, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(@NonNull MenuItem item) {
switch (item.getItemId())  {
case R.id.logout:
FirebaseAuth.getInstance().signOut();
startActivity(new Intent(Main2Activity.this, StartActivity.class).setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP));
return true;
}
return false;
}

class ViewPagerAdapter extends FragmentPagerAdapter {

private ArrayList<Fragment> fragments;
private ArrayList<String> titles;
ViewPagerAdapter(FragmentManager fm) {
super(fm);
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);
titles.add(title);
}
@Nullable
@Override
public CharSequence getPageTitle(int position) {
return titles.get(position);
}
}
private void status(String status) {
reference = FirebaseDatabase.getInstance().getReference("Users").child(firebaseUser.getUid());
HashMap<String, Object> hashMap = new HashMap<>();
hashMap.put("status", status);
reference.updateChildren(hashMap);
}
@Override
protected void onResume() {
super.onResume();
status("online");
}
@Override
protected void onPause() {
super.onPause();
status("offline");
}
}

这就是所谓的错误所在

package com.Interactive.textmefriends.Fragments;
import android.os.Bundle;
import androidx.annotation.NonNull;
import androidx.fragment.app.Fragment;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import android.text.Editable;
import android.text.TextWatcher;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.EditText;
import com.Interactive.textmefriends.Adapter.UserAdapter;
import com.Interactive.textmefriends.Model.User;
import com.Interactive.textmefriends.R;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.Query;
import com.google.firebase.database.ValueEventListener;
import java.util.ArrayList;
import java.util.List;
public class UsersFragment extends Fragment {
private RecyclerView recyclerView;
private UserAdapter userAdapter;
private List<User> mUsers;
EditText search_users;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_users, container, false);
recyclerView = view.findViewById(R.id.recycler_view);
recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(new LinearLayoutManager(getContext()));
mUsers = new ArrayList<>();
readUsers();
search_users = view.findViewById(R.id.search_users);
search_users.addTextChangedListener(new TextWatcher() {
@Override
public void beforeTextChanged(CharSequence charSequence, int i, int i1, int i2) {
}
@Override
public void onTextChanged(CharSequence charSequence, int i, int i1, int i2) {
searchUsers(charSequence.toString().toLowerCase());
}
@Override
public void afterTextChanged(Editable editable) {
}
});
return view;
}
private void searchUsers(String s) {
final FirebaseUser fuser =FirebaseAuth.getInstance().getCurrentUser();
Query query = FirebaseDatabase.getInstance().getReference("Users").orderByChild("search")
.startAt(s)
.endAt(s+"uf8ff");
query.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 fuser != null;
if (!user.getId().equals(fuser.getUid())) {
mUsers.add(user);
}
}
userAdapter = new UserAdapter(getContext(), mUsers, false);
recyclerView.setAdapter(userAdapter);
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});
}
private void readUsers() {
final FirebaseUser firebaseUser = FirebaseAuth.getInstance().getCurrentUser();
DatabaseReference reference = FirebaseDatabase.getInstance().getReference("Users");
reference.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
if (search_users.getText().toString().equals("")) {
mUsers.clear();
for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
User user = snapshot.getValue(User.class);

assert user != null;
assert firebaseUser != null;  
if (!user.getId().equals(firebaseUser.getUid())) { //here
mUsers.add(user);
}
}
userAdapter = new UserAdapter(getContext(), mUsers, false);
recyclerView.setAdapter(userAdapter);
}
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});
}
}

依赖

dependencies {
implementation fileTree(dir: 'libs', include: ['*.jar'])
implementation 'androidx.appcompat:appcompat:1.1.0'
implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
//from here
implementation 'com.google.firebase:firebase-analytics:17.2.2'
implementation 'androidx.legacy:legacy-support-v4:1.0.0'
implementation 'com.google.android.material:material:1.1.0'
implementation 'com.google.firebase:firebase-auth:19.2.0'
implementation 'com.google.firebase:firebase-database:19.2.1'
implementation 'androidx.cardview:cardview:1.0.0'
implementation 'com.rengwuxian.materialedittext:library:2.1.4'
implementation 'de.hdodenhof:circleimageview:3.1.0'
implementation 'com.github.bumptech.glide:glide:4.11.0'
implementation 'com.squareup.retrofit2:retrofit:2.7.1'
implementation 'com.squareup.retrofit2:converter-gson:2.7.1'
implementation 'com.google.firebase:firebase-messaging:20.1.0'
implementation 'com.google.firebase:firebase-storage:19.1.1'
implementation "androidx.fragment:fragment:1.2.1" // this shit
implementation 'com.google.firebase:firebase-ads:18.3.0'
//to here
testImplementation 'junit:junit:4.13'  //this was in .12
androidTestImplementation 'androidx.test.ext:junit:1.1.1'
androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'
}

Answer 1

这与Android Studio更新无关

你在这里看到这条线

user.getId().equals(firebaseUser.getUid())

这是抛出一个NullPointerException，因为它在日志中被清除了，为了避免这种情况，你应该将其更改为

if(user.getId() != null && user.getId().equals(firebaseUser.getUid())

这应该可以避免崩溃，但可能意味着你没有为数据库中的用户正确分配id(因为从技术上讲，所有用户都应该有id(