Android Firebase Facebook登录显示注销按钮，当应用程序重新打开时

Question

public class MainActivity extends AppCompatActivity {

    private LoginButton facebookloginButton;
    private CallbackManager callbackManager;
    private FirebaseAuth mAuth;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mAuth = FirebaseAuth.getInstance();

        facebookloginButton=(LoginButton)findViewById(R.id.facebook_login_button);
        callbackManager=CallbackManager.Factory.create();
        facebookloginButton.setReadPermissions("email", "public_profile");
        facebookloginButton.registerCallback(callbackManager, new FacebookCallback<LoginResult>() {
            @Override
            public void onSuccess(LoginResult loginResult) {
                handleFacebookAccessToken(loginResult.getAccessToken());
            }

            @Override
            public void onCancel() {

            }

            @Override
            public void onError(FacebookException error) {
                Toast.makeText(getApplicationContext(), "Error",Toast.LENGTH_LONG).show();
            }
        });

    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        callbackManager.onActivityResult(requestCode, resultCode, data);
    }

    private void handleFacebookAccessToken(AccessToken token) {


        AuthCredential credential = FacebookAuthProvider.getCredential(token.getToken());
        mAuth.signInWithCredential(credential)
                .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

                            FirebaseUser user = mAuth.getCurrentUser();
                            Intent intent=new Intent(getApplicationContext(),NextActivity.class);
                            //  intent.putExtra("NAME",user.getDisplayName());
                            startActivity(intent);
                            finish();

                        } else {
                            // If sign in fails, display a message to the user.

                            Toast.makeText(getApplicationContext(), "Authentication failed.",
                                    Toast.LENGTH_SHORT).show();

                        }

                        // ...
                    }
                });
    }

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

}

如果应用程序关闭并重新打开，我想让它显示NextActivity

Answer 1

从Facebook成功登录后，您可以将Auth令牌保存在应用程序的Shared Preferences设置中，然后无论何时启动应用程序，您都可以检查存储中是否保存了令牌，如果这意味着用户已经登录，并将其直接重定向到下一页或配置文件页。

以下是您可以做的小片段：

final static String PREFS_NAME = "AUTH" 

public class MainActivity extends AppCompatActivity{

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        settings = getSharedPreferences(PREFS_NAME, MODE_PRIVATE);
        setContentView(R.layout.activity_main);

        // check if user is already logged in
        // i.e. auth token is present or not
        String token = settings.getString("auth_token", null);
        // means user is logged in token was found
        if (token != null) {
            AUTH_TOKEN = token;
            startActivity(new Intent(MainActivity.this, ProfileActivity.class));
        }
    }

        // YOUR REST OF THE CODE ....

});

 @Override
public void onComplete(@NonNull Task<AuthResult> task) {
    if (task.isSuccessful()) {
        // Sign in success, update UI with the signed-in user's information

        FirebaseUser user = mAuth.getCurrentUser();

        // SAVE THE USER DETAILS OR PART OF IT IN SHARED PREFS
        SharedPreferences.Editor editor = settings.edit();
        editor.putString("USER", user);
        editor.apply();

        Intent intent=new Intent(getApplicationContext(),NextActivity.class);
        //  intent.putExtra("NAME",user.getDisplayName());
        startActivity(intent);
        finish();

    } else {
        // If sign in fails, display a message to the user.

        Toast.makeText(getApplicationContext(), "Authentication failed.",
                Toast.LENGTH_SHORT).show();

    }

    // ...
}

这将起作用，因为每次在oncreate方法中启动应用程序时，如果auth文件存在，它将直接将用户发送到nextactivity。