如何获取有关其电子邮件在 Firebase 中已知的用户的信息？

Question

我在 Firebase 中有以下数据：

（我还不能在 Stackoverflow 中附加图片）：

有一个根节点 -> 根有一个名为“NewStaffRequests”的子节点。 “NewStaffRequests”有多个具有唯一 ID 的用户。在每个唯一 id 下，存在一个特定用户的电子邮件 ID 和角色密钥。 “角色”键可以具有诸如“培训师”之类的值。

电子邮件 ID 已在身份验证系统中注册。未来，会有更多这样的具有唯一 id、email-id 和角色的用户。我想登录，检索其 email-id 是从 Activity 中的 email-id TextView 获得的用户的角色，在“NewStaffRequests”中找到这个 email-id 并获取该用户的角色。我为此编写了以下代码。但是，对象 'StaffUser value' 只会为空。请指教！

@Override
 protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_staff_login);

        mAuth = FirebaseAuth.getInstance();

        heading = (TextView) findViewById(R.id.heading);
        note = (TextView) findViewById(R.id.note);
        email = (EditText) findViewById(R.id.enterEmail);
        pwd = (EditText) findViewById(R.id.enterPassword);

        spinner = (Spinner) findViewById(R.id.roles_spinner);

        login = (Button) findViewById(R.id.login);


        login.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v)
            {

                final String staffEmail = email.getText().toString().trim();
                final String password = pwd.getText().toString().trim();

                if(TextUtils.isEmpty(staffEmail))
                {
                    Toast.makeText(getApplicationContext(), "You must enter your E-Mail!", Toast.LENGTH_SHORT).show();
                    return;
                }
                if(TextUtils.isEmpty(password))
                {
                    Toast.makeText(getApplicationContext(), "You must enter your Password!", Toast.LENGTH_SHORT).show();
                    return;
                }

          }

                mAuth.signInWithEmailAndPassword(staffEmail,password).addOnCompleteListener(StaffLogin.this, new OnCompleteListener<AuthResult>()
                {
                    @Override
                    public void onComplete(@NonNull Task<AuthResult> task)
                    {
                        Log.d(TAG, "successfull login : " + task.isSuccessful());

                        if (!task.isSuccessful()){
                            Toast.makeText(StaffLogin.this, "Authentication failed." + task.getException(), Toast.LENGTH_LONG).show();
                        }
                        else {

                            DatabaseReference root = FirebaseDatabase.getInstance().getReference();
                            Query reference = root.child("NewStaffRequests").orderByChild("email").equalTo(staffEmail);
                            reference.addListenerForSingleValueEvent(new ValueEventListener() {
                                @Override
                                public void onDataChange(DataSnapshot dataSnapshot) {
                                    if (dataSnapshot.getChildrenCount() > 0) {

                                        StaffUser value = dataSnapshot.getValue(StaffUser.class);
                                        String staffRole = value.role;

                                        if(staffRole.equals("Fitness Trainer"))
                                        {
                                            startActivity(new Intent(StaffLogin.this, RMLanding.class));
                                            finish();
                                        }
                                        else
                                        {
                                            Toast.makeText(getApplicationContext(), "The user is someone else", Toast.LENGTH_SHORT).show();

                                        }


                                    }
                                    else{
                                        Toast.makeText(getApplicationContext(), "Something went wrong", Toast.LENGTH_SHORT).show();
                                    }
                                }

                                @Override
                                public void onCancelled(DatabaseError databaseError) {

                                }
                            });
                        }
                    }
                });    
            }
        });
    }
}

而且，以下是 StaffUser 类：

public class StaffUser {

    public String email, name, role;
    public Boolean approvalStatus;

    public StaffUser() {
        // Default constructor required for calls to DataSnapshot.getValue(User.class)
    }

    public StaffUser(String _email, String _name,String _role,Boolean _approvalStatus) {

        this.email = _email;
        this.name = _name;
        this.role = _role;
        this.approvalStatus = _approvalStatus;
    }
}

以下是错误信息：

java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.equals(java.lang.Object)' on a null object reference.

这个错误指向的行是：

String staffRole = value.role;

在亚历克斯的建议下做出的改变：

mAuth.signInWithEmailAndPassword(staffEmail,password).addOnCompleteListener(StaffLogin.this, new OnCompleteListener<AuthResult>()
                {
                    @Override
                    public void onComplete(@NonNull Task<AuthResult> task)
                    {
                        Log.d(TAG, "successfull login : " + task.isSuccessful());

                        if (!task.isSuccessful()){
                            Toast.makeText(StaffLogin.this, "Authentication failed." + task.getException(), Toast.LENGTH_LONG).show();
                        }
                        else {

                            DatabaseReference root = FirebaseDatabase.getInstance().getReference();
                            Query reference = root.child("NewStaffRequests").orderByChild("email").equalTo(staffEmail);
                            reference.addListenerForSingleValueEvent(new ValueEventListener() {
                                @Override
                                public void onDataChange(DataSnapshot dataSnapshot) {
                                    if (dataSnapshot.getChildrenCount() > 0) {


                                        //Toast.makeText(StaffLogin.this, "datasnapshot value" + dataSnapshot.getValue(StaffUser.class), Toast.LENGTH_LONG).show();
                                        StaffUser value = dataSnapshot.getValue(StaffUser.class);//When I attach the debugger on this line, I can see that 'value' is null, but dataSnapshot.getValue(StaffUser.class) is showing the stored database values from firebase.
                                        Log.d(TAG, "datasnapshot value" + value.getRole());

                                        String staffRole = value.getRole();

                                        if(staffRole.equals("Rescue Manager"))
                                        {
                                            startActivity(new Intent(StaffLogin.this, RMLanding.class));
                                            finish();
                                        }
                                        else
                                        {
                                            Toast.makeText(getApplicationContext(), "The user is someone else", Toast.LENGTH_SHORT).show();

                                        }


                                    }
                                    else{
                                        Toast.makeText(getApplicationContext(), "Something went wrong", Toast.LENGTH_SHORT).show();
                                    }
                                }

                                @Override
                                public void onCancelled(DatabaseError databaseError) {

                                }
                            });


                        }



                    }
                });

Answer 1

如果你得到这个错误，java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.equals(java.lang.Object)' on a null object reference，这意味着staffRole字符串是null。

要解决这个问题，你需要使用下面这行代码：

String staffRole = value.getRole();

这也意味着你需要像这样在你的模型类中添加这个方法：

public String getRole() {
    return role;
}

请注意，您需要向所有字段添加公共 getter，并且字段本身必须是私有的，而不是像我在您的课程中看到的那样公开。你的类应该是这样的：

public class StaffUser {
    private String email, name, role;
    private boolean approvalStatus;

    public StaffUser() {}

    public StaffUser(String email, String name, String role, Boolean approvalStatus) {
        this.email = email;
        this.name = name;
        this.role = role;
        this.approvalStatus = approvalStatus;
    }

    public String getEmail() {return email;}

    public String getName() {return name;}

    public String getRole() {return role;}

    public boolean getApprovalStatus() {return approvalStatus;}
}

要获取实际对象，请使用以下代码：

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
Query query = rootRef.child("NewStaffRequests").orderByChild("email").equalTo(staffEmail);
ValueEventListener eventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            StaffUser value = dataSnapshot.getValue(StaffUser.class);
            Log.d("TAG", value.getRole());
        }
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {}
};
query.addListenerForSingleValueEvent(eventListener);