执行我的应用程序时，出现以下错误：
java.lang.NullPointerException：无法为child（）中的参数'pathString'传递null
但是我之前没有收到此错误。有人可以帮助我吗？
请查看错误控制台，并在Java代码上方
控制台错误：
E/AndroidRuntime: FATAL EXCEPTION: main
Process: br.com.devbrains.nerdspace, PID: 12393
java.lang.RuntimeException: Unable to start activity ComponentInfo{br.com.devbrains.nerdspace/br.com.devbrains.nerdspace.activity.MainActivity}: java.lang.NullPointerException: Can't pass null for argument 'pathString' in child()
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2812)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2890)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1611)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:171)
at android.app.ActivityThread.main(ActivityThread.java:6633)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:547)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:823)
Caused by: java.lang.NullPointerException: Can't pass null for argument 'pathString' in child()
at com.google.firebase.database.DatabaseReference.child(com.google.firebase:firebase-database@@16.0.3:101)
at br.com.devbrains.nerdspace.fragment.MessagesFragment.onCreateView(MessagesFragment.java:85)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:2439)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1460)
at android.support.v4.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManager.java:1784)
at android.support.v4.app.BackStackRecord.executeOps(BackStackRecord.java:797)
at android.support.v4.app.FragmentManagerImpl.executeOps(FragmentManager.java:2625)
at android.support.v4.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2411)
at android.support.v4.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManager.java:2366)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:2273)
at android.support.v4.app.FragmentManagerImpl.dispatchStateChange(FragmentManager.java:3273)
at android.support.v4.app.FragmentManagerImpl.dispatchActivityCreated(FragmentManager.java:3229)
at android.support.v4.app.FragmentController.dispatchActivityCreated(FragmentController.java:201)
at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:620)
at android.support.v7.app.AppCompatActivity.onStart(AppCompatActivity.java:178)
at br.com.devbrains.nerdspace.activity.MainActivity.onStart(MainActivity.java:411)
at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1335)
at android.app.Activity.performStart(Activity.java:7104)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2775)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2890)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1611)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:171)
at android.app.ActivityThread.main(ActivityThread.java:6633)
MessagesFragment.java
MessagesFragment中的第一个错误，该错误发生在MessagesDbRef中，但是firebase不为空。
public class MessagesFragment extends Fragment {
private static final String TAG = MessagesFragment.class.getSimpleName();
private FirebaseAuth mAuth;
private FirebaseUser user;
private DatabaseReference userDbRef;
private DatabaseReference messagesDbRef;
private DatabaseReference conversationsDbRef;
private FirebaseRecyclerAdapter firebaseRecyclerAdapter;
private RecyclerView recyclerViewConversations;
private Context context;
ImageView imgViewNoMessages;
TextView txtNoMessages;
private String currentUserId;
public MessagesFragment() {
}
@Override
public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View messagesView = inflater.inflate(R.layout.fragment_messages, container, false);
imgViewNoMessages = (ImageView) messagesView.findViewById(R.id.image_no_messages);
txtNoMessages = (TextView) messagesView.findViewById(R.id.text_no_messages);
this.context = getContext();
mAuth = FirebaseAuth.getInstance();
user = mAuth.getCurrentUser();
if (user != null) {
currentUserId = user.getUid();
}
recyclerViewConversations = (RecyclerView) messagesView.findViewById(R.id.rv_conversations);
userDbRef = FirebaseDatabase.getInstance().getReference().child("Users");
userDbRef.keepSynced(true);
conversationsDbRef = FirebaseDatabase.getInstance().getReference().child("Chat").child(currentUserId);
conversationsDbRef.keepSynced( true );
messagesDbRef = FirebaseDatabase.getInstance().getReference().child("Messages").child(currentUserId);
messagesDbRef.keepSynced(true);
LinearLayoutManager linearLayoutManager = new LinearLayoutManager(getContext());
linearLayoutManager.setReverseLayout(true);
linearLayoutManager.setStackFromEnd(true);
recyclerViewConversations.setHasFixedSize(true);
recyclerViewConversations.setLayoutManager(linearLayoutManager);
return messagesView;
}
MainActivity.java
这里的错误显示在onStart（）方法中。
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
final AppBarLayout.LayoutParams params = (AppBarLayout.LayoutParams) toolbar.getLayoutParams();
mAuth = FirebaseAuth.getInstance();
user = mAuth.getCurrentUser();
nerdspaceProgressBar = NerdspaceProgressBar.getInstance();
//TODO: Ação do botão FAB
fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
startActivity(new Intent(getApplicationContext(), CreateNewsActivity.class));
}
});
if (user != null) {
String userUid = user.getUid();
currentUserDbRef = FirebaseDatabase.getInstance().getReference().child("Users").child(userUid);
currentUserDbRef.addValueEventListener(new ValueEventListener() {
@SuppressLint("NewApi")
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
if (dataSnapshot.exists()) {
image = (String) dataSnapshot.child("image").getValue();
if (image == null || image.equals("default")) {
if (getApplicationContext() != null) {
GlideApp.with(getApplicationContext())
.load(image)
.placeholder(R.drawable.stormtropper)
.error(R.drawable.stormtropper)
.fitCenter()
.diskCacheStrategy(DiskCacheStrategy.ALL)
.listener(new RequestListener<Drawable>() {
@Override
public boolean onLoadFailed(@Nullable GlideException e, Object model, Target<Drawable> target, boolean isFirstResource) {
Log.e(TAG, "Error loading image", e);
return false;
}
@Override
public boolean onResourceReady(Drawable resource, Object model, Target<Drawable> target, DataSource dataSource, boolean isFirstResource) {
return false;
}
})
.into(civNavHeader);
}
}
String name = (String) dataSnapshot.child("name").getValue();
String email = user.getEmail();
if (getApplicationContext() != null) {
GlideApp.with(getApplicationContext())
.load(image)
.placeholder(R.drawable.stormtropper)
.error(R.drawable.stormtropper)
.fitCenter()
.diskCacheStrategy(DiskCacheStrategy.ALL)
.listener(new RequestListener<Drawable>() {
@Override
public boolean onLoadFailed(@Nullable GlideException e, Object model, Target<Drawable> target, boolean isFirstResource) {
Log.e(TAG, "Error loading image", e);
return false;
}
@Override
public boolean onResourceReady(Drawable resource, Object model, Target<Drawable> target, DataSource dataSource, boolean isFirstResource) {
return false;
}
})
.into(civNavHeader);
}
tvNavHeaderUserName.setText(capitalizeFully(name));
tvNavHeaderUserEmail.setText(email);
}
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});
}
navigationView.setNavigationItemSelectedListener(this);
}
@Override
protected void onStart() {
super.onStart();
if (user == null) {
Intent intent = new Intent(this, LoginActivity.class);
startActivity(intent);
finish();
} else {
currentUserDbRef.child("online").setValue("true");
civNavHeader.setBorderColor(getResources().getColor(R.color.colorOnline));
}
}
答案 0 :(得分：0)
似乎您没有共享类的所有代码。
所以我只有猜测；
if (user != null) {
currentUserId = user.getUid();
}
这些行说如果用户为空，则currentUserId将为空。
conversationsDbRef = FirebaseDatabase.getInstance().getReference().child("Chat")
.child(currentUserId);
在这行代码中，似乎传递的参数 currentUserId 为null，并且该null是NullPointerException的原因