爲什麼setReadPermissions呈現NullPointerException在Facebook登錄在Android工作室

-1

我想將Facebook登錄集成到我的應用程序，但當我嘗試進入活動時，我的按鈕是。爲什麼setReadPermissions呈現NullPointerException在Facebook登錄在Android工作室

我跟着這個教程：http://alvarez.tech/login-facebook-en-android/

我的活動是這樣的：

@Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     _THIS=this; 
     setContentView(R.layout.connexion_layout); 

     if(savedInstanceState!= null) return; 

     FrameLayout frameLayout = (FrameLayout)findViewById(R.id.fragment_container); 

     connexion0 = new connexion0Fragment(); 
     connexion1 = new connexion1Fragment(); 

     changeFragment(0); 
     connexionViaFacebook(); 

    } 

    public void connexionViaFacebook(){ 
     callbackManager = CallbackManager.Factory.create(); 

     loginButton = (LoginButton) findViewById(R.id.loginButton); 

     loginButton.setReadPermissions(Arrays.asList("email")); 

     loginButton.registerCallback(callbackManager, new FacebookCallback<LoginResult>() { 
      @Override 
      public void onSuccess(LoginResult loginResult) { 
       goMainScreen(); 
      } 

      @Override 
      public void onCancel() { 
       Toast.makeText(getApplicationContext(), R.string.cancel_login, Toast.LENGTH_SHORT).show(); 
      } 

      @Override 
      public void onError(FacebookException error) { 
       Toast.makeText(getApplicationContext(), R.string.error_login, Toast.LENGTH_SHORT).show(); 
      } 
     }); 
    }

的錯誤是：

java.lang.NullPointerException: Attempt to invoke virtual method 'void com.facebook.login.widget.LoginButton.setReadPermissions(java.util.List)' on a null object reference

來源

2016-11-16 Elgallati Noreddine