Facebook authentication without login button

@erdomester, @sromku

Facebook launch new sdk version 4.x where Session is deprecated,

There new concept of login as from facebook

LoginManager and AccessToken – These new classes perform Facebook
Login

So, Now you can access Facebook authentication without login button as

layout.xml

    <Button
            android:id="@+id/btn_fb_login"
            .../>

MainActivity.java

private CallbackManager mCallbackManager;

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

    FacebookSdk.sdkInitialize(this.getApplicationContext());

    mCallbackManager = CallbackManager.Factory.create();

    LoginManager.getInstance().registerCallback(mCallbackManager,
            new FacebookCallback<LoginResult>() {
                @Override
                public void onSuccess(LoginResult loginResult) {
                    Log.d("Success", "Login");

                }

                @Override
                public void onCancel() {
                    Toast.makeText(MainActivity.this, "Login Cancel", Toast.LENGTH_LONG).show();
                }

                @Override
                public void onError(FacebookException exception) {
                    Toast.makeText(MainActivity.this, exception.getMessage(), Toast.LENGTH_LONG).show();
                }
            });

    setContentView(R.layout.activity_main);

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

    btn_fb_login.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
              LoginManager.getInstance().logInWithReadPermissions(this, Arrays.asList("public_profile", "user_friends"));
        }
    });

}

Edit

If you don’t add the following, it won’t work (rightly pointed out by @Daniel Zolnai in comment below):

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