java - 如何从 Firebase 实时数据库检索用户用户名以获取欢迎回复消息？

Question

我有一个 android studio 项目，用户使用电子邮件地址和密码登录。用户的用户名在注册时存储在 Firebase 的实时数据库中。我如何从数据库中检索用户名，以便在成功登录后显示欢迎回来(用户名)消息？

我已附加主屏幕 java，这是我希望显示消息的位置。我还附上了登录java，用户可以在其中输入电子邮件和密码。用户输入其详细信息和用户类别的寄存器类别。

提前致谢，我对代码很陌生，请原谅我的无知。

package com.example.securityapp;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;


import com.google.firebase.auth.FirebaseAuth;

public class home extends AppCompatActivity {

    Button training;
    Button signOut;
    Button loginPage;
    private FirebaseAuth mAuth;

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

        training = (Button) findViewById(R.id.training_button);
        signOut = (Button) findViewById(R.id.sign_out);
        mAuth = FirebaseAuth.getInstance();
        FirebaseAuth mAuth;


    }




    public void signOutUser() {
        mAuth.signOut();
        Toast.makeText(home.this, "Sign out successful!", Toast.LENGTH_LONG).show();
        Intent intent_signout = new Intent(home.this, login.class);
        startActivity(intent_signout);
        finish();

    }

    public void SignoutOnClick(View view) {
        signOut.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                signOutUser();
            }
        });
    }


    public void TrainingOnClick(View view) {
        training.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent_training = new Intent(home.this, training.class);
                startActivity(intent_training);
                finish();
            }
        });
    }

        public void loginOnClick (View view){
            loginPage.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    Intent intent_login = new Intent(home.this, register.class);
                    startActivity(intent_login);
                    finish();
                }
            });
        }
    }

package com.example.securityapp;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.firebase.auth.AuthResult;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;

public class register extends AppCompatActivity {

    private FirebaseAuth mAuth;
    EditText emailReg, passwordReg, password2, roleReg, officeReg;
    Button regButton;
    DatabaseReference databaseUsers;
    EditText usernameReg;
    FirebaseDatabase database = FirebaseDatabase.getInstance();


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

        emailReg = (EditText) findViewById(R.id.regEmail);
        usernameReg = (EditText) findViewById(R.id.regUsername);
        passwordReg = (EditText) findViewById(R.id.regPassword);
        regButton = (Button) findViewById(R.id.register_Button);
        password2 = (EditText) findViewById(R.id.confirm_password);
        roleReg = (EditText) findViewById(R.id.regRole);
        officeReg = (EditText) findViewById(R.id.regOffice);
        databaseUsers = database.getReference();
        mAuth = FirebaseAuth.getInstance();
    }


    public void registerUser() {

        final String email = emailReg.getText().toString();
        final String password = passwordReg.getText().toString();
        String pass2 = password2.getText().toString();
        if(!pass2.equals(password))
        {
            Toast.makeText(register.this, "Passwords Do Not Match",
                    Toast.LENGTH_SHORT).show();
            return;
        }
        //Code taken from https://firebase.google.com/docs/auth/android/start on 10/11/2019
        mAuth.createUserWithEmailAndPassword(email, password)
                .addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
                    @Override
                    public void onComplete(@NonNull Task<AuthResult> task) {
                        if (task.isSuccessful()) {
                            // Sign in success, update UI with the signed-in user's information
                            insertDataDB();

                            Intent intent_signup = new Intent(register.this, home.class);

                            startActivity(intent_signup);
                            finish();
                            FirebaseUser user = mAuth.getCurrentUser();
                            Toast.makeText(register.this, "Authentication Successful!",
                                    Toast.LENGTH_SHORT).show();
                        } else {
                            // If sign in fails, display a message to the user.
                            Toast.makeText(register.this, "Authentication failed.",
                                    Toast.LENGTH_SHORT).show();
                        }

                        // ...
                    }
                });

    }


    public void registerOnClick(View view)
    {
        regButton.setOnClickListener(new View.OnClickListener()
        {
            @Override
            public void onClick(View v)
            {

                registerUser();


            }
        });


    }

    public void insertDataDB()
    {
        String username = usernameReg.getText().toString();
        String job = roleReg.getText().toString();
        String email = emailReg.getText().toString();
        String office = officeReg.getText().toString();


        String id = databaseUsers.push().getKey();

        Users user1 = new Users(username, job, email, office);
        databaseUsers.child(id).setValue(user1);


    }
}

package com.example.securityapp;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;

import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.firebase.auth.AuthResult;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;

public class login extends AppCompatActivity
        //implements View.OnClickListener
    {
        Button signUp;
        Button login;
        EditText etEmail;
        EditText etPassword;
        ProgressBar bar;
        FirebaseAuth mAuth;


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

            signUp = (Button) findViewById(R.id.signUp_button);
            login = (Button) findViewById(R.id.login_button);
            etEmail = (EditText)findViewById(R.id.email_input);
            etPassword = (EditText)findViewById(R.id.password_input);
            bar = (ProgressBar) findViewById(R.id.progressBar);
            bar.setVisibility(View.GONE);
            mAuth = FirebaseAuth.getInstance();
        }

        @Override
        public void onStart()
        {
            super.onStart();
            // Check if user is signed in (non-null) and update UI accordingly.
            FirebaseUser currentUser = mAuth.getCurrentUser();
        }

        //Code taken from https://firebase.google.com/docs/auth/android/password-auth on 06/11/2019
        public void loginUser()
        {
            final String email = etEmail.getText().toString();
            String password = etPassword.getText().toString();

            if(email.isEmpty()&&password.isEmpty())
            {
                Toast.makeText(login.this, "Email and password cannot be empty.",
                        Toast.LENGTH_SHORT).show();
                bar.setVisibility(View.GONE);
            }else if(email.isEmpty())
            {
                Toast.makeText(login.this, "Email cannot be empty.",
                        Toast.LENGTH_SHORT).show();
                bar.setVisibility(View.GONE);
            }else if(password.isEmpty())
            {
                Toast.makeText(login.this, "Password cannot be empty.",
                        Toast.LENGTH_SHORT).show();
                bar.setVisibility(View.GONE);
            }else

                mAuth.signInWithEmailAndPassword(email, password)
                        .addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
                            @Override
                            public void onComplete(@NonNull Task<AuthResult> task) {
                                if (task.isSuccessful())
                                {
                                    //Log.d(TAG, "signInWithEmail:success");
                                    // FirebaseUser user = mAuth.getCurrentUser();
                                    bar.setVisibility(View.VISIBLE);
                                    Intent intent_home = new Intent(login.this, home.class);
                                    startActivity(intent_home);
                                    finish();
                                    Toast.makeText(login.this, "Login successful",
                                            Toast.LENGTH_SHORT).show();
                                    //updateUI(user);
                                } else {
                                    // If sign in fails, display a message to the user.
                                    //Log.w(TAG, "signInWithEmail:failure", task.getException());
                                    Toast.makeText(login.this, "Incorrect Email or Password.",
                                            Toast.LENGTH_SHORT).show();
                                    bar.setVisibility(View.GONE);

                                    //updateUI(null);
                                }

                                // ...
                            }
                        });
            }





        public void loginOnClick (View view)
{
    login.setOnClickListener(new View.OnClickListener()
    {
        @Override
        public void onClick(View v)
        {
            bar.setVisibility(View.VISIBLE);
            loginUser();

        }
    });
}

        public void RegisterOnClick (View view)
        {
            signUp.setOnClickListener(new View.OnClickListener()
            {
                @Override
                public void onClick(View v)
                {
                    Intent intent_reg = new Intent(login.this, register.class);
                    startActivity(intent_reg);
                    finish();
                }
            });
        }


}

package com.example.securityapp;

public class Users {

    String username;
    String job;
    String email;
    String office;

    public Users() {

    }

    public Users(String username, String job, String email, String office) {
        this.username = username;
        this.job = job;
        this.email = email;
        this.office = office;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getJob() {
        return job;
    }

    public void setJob(String job) {
        this.job = job;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getOffice() {
        return office;
    }

    public void setOffice(String office) {
        this.office = office;
    }
}

Answer 1

尝试用这个...

FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();
if (user != null) {
        String name = user.getDisplayName();
        String email = user.getEmail();
        Uri photoUrl = user.getPhotoUrl();
    // User is signed in
} else {
    // No user is signed in
}

关注 Firebase documnets