即使用户关闭应用程序后，我也试图让用户保持登录到我的聊天应用程序。因此，他们退出帐户的唯一方法是单击注销按钮。
到目前为止，用户确实保持登录状态，但当我单击注销按钮时，应用程序崩溃了。这是我得到的错误
Attempt to invoke virtual method 'java.lang.String com.google.firebase.auth.FirebaseUser.getUid()' on a null object reference
at com.example.chatterbox.ChatsFragment.onCreateView(ChatsFragment.java:54)
问题是该错误来自不同的文件。有人可以帮我吗？
public class LoginActivity extends AppCompatActivity {
private FirebaseAuth mAuth;
private ProgressDialog loadingBar;
private Button LoginButton ;
private EditText UserEmail, UserPassword;
private TextView NeedNewAccountLink, ForgetPasswordLink;
private DatabaseReference UsersRef;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_login);
RelativeLayout relativeLayout = findViewById(R.id.layout);
AnimationDrawable animationDrawable = (AnimationDrawable) relativeLayout.getBackground();
animationDrawable.setEnterFadeDuration(5000);
animationDrawable.setExitFadeDuration(5000);
animationDrawable.start();
mAuth = FirebaseAuth.getInstance();
UsersRef = FirebaseDatabase.getInstance().getReference().child("Users");
InitializeFields();
if (UsersRef != null) {
Intent intent = new Intent(LoginActivity.this, MainActivity.class);
startActivity(intent);
finish();
}
NeedNewAccountLink.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
SendUserToRegisterActivity();
}
});
LoginButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
AllowUserToLogin();
}
});
}
private void AllowUserToLogin () {
String email = UserEmail.getText().toString();
String password = UserPassword.getText().toString();
if (TextUtils.isEmpty(email)) {
Toast.makeText(this, "Please enter your email", Toast.LENGTH_SHORT).show();
}
if (TextUtils.isEmpty(password)) {
Toast.makeText(this, "Please enter your password", Toast.LENGTH_SHORT).show();
} else {
loadingBar.setTitle("Logging In");
loadingBar.setMessage("Please wait...");
loadingBar.setCanceledOnTouchOutside(true);
loadingBar.show();
mAuth.signInWithEmailAndPassword(email, password)
.addOnCompleteListener(new OnCompleteListener<AuthResult>() {
@Override
public void onComplete(@NonNull Task<AuthResult> task) {
if (task.isSuccessful()) {
String currentUserId = mAuth.getCurrentUser().getUid();
String deviceToken = FirebaseInstanceId.getInstance().getToken();
UsersRef.child(currentUserId).child("device_token")
.setValue(deviceToken)
.addOnCompleteListener(new OnCompleteListener<Void>() {
@Override
public void onComplete(@NonNull Task<Void> task) {
if (task.isSuccessful()) {
SendUserToMainActivity();
Toast.makeText(LoginActivity.this, "Logged in successfully", Toast.LENGTH_SHORT).show();
loadingBar.dismiss();
}
}
});
} else {
String message = task.getException().toString();
Toast.makeText(LoginActivity.this, "Error:" + message, Toast.LENGTH_SHORT).show();
loadingBar.dismiss();
}
}
});
}
}
private void InitializeFields () {
LoginButton = (Button) findViewById(R.id.login_button);
UserEmail = (EditText) findViewById(R.id.login_email);
UserPassword = (EditText) findViewById(R.id.login_password);
NeedNewAccountLink = (TextView) findViewById(R.id.need_new_account_link);
ForgetPasswordLink = (TextView) findViewById(R.id.forget_password_link);
loadingBar = new ProgressDialog(this);
}
private void SendUserToMainActivity () {
Intent mainIntent = new Intent(LoginActivity.this, MainActivity.class);
mainIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);
startActivity(mainIntent);
finish();
}
private void SendUserToRegisterActivity () {
Intent registerIntent = new Intent(LoginActivity.this, RegisterActivity.class);
startActivity(registerIntent);
}
错误行:
currentUserID = mAuth.getCurrentUser().getUid();
这就是我检查用户是否已登录的方法。如果是，我会将其发送到 MainActivity。如果不是，它们将停留在 LoginActivity
if (UsersRef != null) {
Intent intent = new Intent(LoginActivity.this, MainActivity.class);
startActivity(intent);
finish();
}
最佳答案
你打电话
mAuth = FirebaseAuth.getInstance();
UsersRef = FirebaseDatabase.getInstance().getReference().child("Users");
然后
if (UsersRef != null) {
//do something
}
这有点奇怪，因为您需要知道当前是否有有效用户登录 Firebase。这个 fragment 也许有用:
FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();
if (user != null) {
// User is signed in
} else {
// No user is signed in
}
但是你正在检查变量UsersRef(我猜是一个DatabaseReference)是否为空...实际上你只是给了它一个值!!!
关于java - 保持用户登录 Java Firebase，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/56201489/