Android java.lang.String com.google.firebase.auth.FirebaseUser.getEmail（）”在空对象引用上

我想用文本视图在主页上显示用户电子邮件我试图使用getCurrentUser.getEmail获取电子邮件，但它显示了一个错误

java.lang.NullPointerException：尝试对空对象引用调用虚拟方法“java.lang.String com.google.firebase.auth.FirebaseUser.getEmail”

这是密码

public class Homepage extends AppCompatActivity {
protected FirebaseAuth auth = FirebaseAuth.getInstance();
@Override
    public void onStart(){
        super.onStart();
       TextView tt1 = findViewById(R.id.tt1);
        String email = auth.getCurrentUser().getEmail();
        tt1.setText(email);
    }
}

Login.java

public class Login extends AppCompatActivity {
    private EditText inputEmail, inputPassword;
    private FirebaseAuth auth;
    private Button btnSignup, btnLogin, btnReset;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        //Get Firebase auth instance
        auth = FirebaseAuth.getInstance();

        if (auth.getCurrentUser() != null) {
            startActivity(new Intent(Login.this, Homepage.class));
            finish();
        }

        // set the view now
        setContentView(R.layout.activity_login);

        // Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        // setSupportActionBar(toolbar);

        inputEmail = (EditText) findViewById(R.id.email);
        inputPassword = (EditText) findViewById(R.id.password);
        btnSignup = (Button) findViewById(R.id.btn_signup);
        btnLogin = (Button) findViewById(R.id.btn_login);
        btnReset = (Button) findViewById(R.id.btn_reset_password);

        //Get Firebase auth instance
        auth = FirebaseAuth.getInstance();

        btnSignup.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                startActivity(new Intent(Login.this, SignUp.class));
            }
        });

        btnReset.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                startActivity(new Intent(Login.this, ResetPassword.class));
            }
        });

        btnLogin.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String email = inputEmail.getText().toString();
                final String password = inputPassword.getText().toString();

                if (TextUtils.isEmpty(email)) {
                    Toast.makeText(getApplicationContext(), "Enter email address!", Toast.LENGTH_SHORT).show();
                    return;
                }

                if (TextUtils.isEmpty(password)) {
                    Toast.makeText(getApplicationContext(), "Enter password!", Toast.LENGTH_SHORT).show();
                    return;
                }

                //authenticate user
                auth.signInWithEmailAndPassword(email, password)
                        .addOnCompleteListener(Login.this, new OnCompleteListener<AuthResult>() {
                            @Override
                            public void onComplete(@NonNull Task<AuthResult> task) {
                                // If sign in fails, display a message to the user. If sign in succeeds
                                // the auth state listener will be notified and logic to handle the
                                // signed in user can be handled in the listener.

                                if (!task.isSuccessful()) {
                                    // there was an error
                                    if (password.length() < 6) {
                                        inputPassword.setError(getString(R.string.minimum_password));
                                    } else {
                                        Toast.makeText(Login.this, getString(R.string.auth_failed), Toast.LENGTH_LONG).show();
                                    }
                                } else {
                                    Intent intent = new Intent(Login.this, Homepage.class);
                                    startActivity(intent);
                                    finish();
                                }
                            }
                        });
            }
        });
    }
}

Manifest.xml

 <activity android:name=".Login"> <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter></activity>

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如果用户尚未登录，则auth.getCurrentUser将返回null。您必须检查ifauth.getCurrentUser！=空的{ 字符串email=auth.getCurrentUser.getEmail； tt1.1电子邮件；

---

}

是的，已经证明用户没有登录，但我认为我的登录类代码没有任何错误。也许你可以看看我已经上传了登录。java用户在主页上借出的方式是什么，你的启动活动是什么？您可以从清单中验证启动活动吗？Login.java将是启动活动，登录后它将重定向到主页，这是访问主页的唯一方法，如果用户尚未登录，它将使您返回登录页面