尝试在空对象引用上调用接口方法 com.google.firebase.auth.FirebaseAuth$AuthStateListener.onAuthStateChanged'

Question

应用程序在查看详细信息时被强制停止

我已经尝试了不同的方法来连接到我的 firebase 用户 ID，但它给出了空指针异常并显示尝试调用接口方法Firebase 身份验证状态侦听器引发错误

查看详情.class

public class ViewDetails extends AppCompatActivity {
    private DatabaseReference myref;
    private FirebaseAuth mAuth;
    private FirebaseAuth.AuthStateListener mAuthListener;
    private FirebaseDatabase mFirebaseDatabase;
    private String userId;
    ListView listView;
    private TextView name,email,phone,shopname,shopaddress;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_view_details);
        setContentView(R.layout.activity_login);getWindow().setBackgroundDrawableResource(R.drawable.inventorybackground);
        listView=(ListView)findViewById(R.id.listview);
        name=(TextView)findViewById(R.id.name);
        email=(TextView)findViewById(R.id.email);
        phone=(TextView)findViewById(R.id.phonenumber);
        shopname=(TextView)findViewById(R.id.shopname);
        shopaddress=(TextView)findViewById(R.id.shopaddress);
        mAuth=FirebaseAuth.getInstance();
        mFirebaseDatabase=FirebaseDatabase.getInstance();
        myref=mFirebaseDatabase.getReference();
        FirebaseUser user=mAuth.getCurrentUser();
        userId=user.getUid();
        myref.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                showData(dataSnapshot);
            }
            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {
            }
        });
    }
    private void showData(DataSnapshot dataSnapshot) {
        for(DataSnapshot ds:dataSnapshot.getChildren())
        {
            getdetails get=new getdetails();
            get.setName(ds.child(userId).getValue(getdetails.class).getName());
            get.setEmail(ds.child(userId).getValue(getdetails.class).getEmail());
            get.setPhone(ds.child(userId).getValue(getdetails.class).getPhone());
            get.setShopname(ds.child(userId).getValue(getdetails.class).getShopname());
            get.setShopadd(ds.child(userId).getValue(getdetails.class).getShopadd());
            ArrayList<String> array = new ArrayList<>();
            array.add(get.getName());
            array.add(get.getEmail());
            array.add(get.getPhone());
            array.add(get.getShopname());
            array.add(get.getShopadd());
            ArrayAdapter adapter=new ArrayAdapter(this,android.R.layout.simple_list_item_1,array);
            listView.setAdapter(adapter);
        }
    }
    @Override
    protected void onStart() {
        super.onStart();
        mAuth.addAuthStateListener(mAuthListener);
    }
    @Override
    protected void onStop() {
        super.onStop();
        if(mAuthListener!=null)
        {
            mAuth.removeAuthStateListener(mAuthListener);
        }
    }
    private void toastMessage(String message)
    {
        Toast.makeText(this,message,Toast.LENGTH_LONG).show();
    }
}

怎么了？

Answer 1

你得到 null mAuthListener因为永远不会实例化。

在你的onCreate()中执行此操作

mAuthListener = new FirebaseAuth.AuthStateListener() {
            @Override
            public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) {
                FirebaseUser user = firebaseAuth.getCurrentUser();
                if (user != null) {
                    // Your logic
                }
            }
        };