java.lang.NullPointerException facebookでログインしてください。

Question

facebookでログインしている間、このエラーが何度も繰り返されています。私は理解できません。親切に助けてください。

public class LoginActivity extends AppCompatActivity { 

    private CallbackManager callbackManager; 
    private AccessTokenTracker accessTokenTracker; 
    private ProfileTracker profileTracker; 

    //Facebook login button 
    private FacebookCallback<LoginResult> callback = new FacebookCallback<LoginResult>() { 
     @Override 
     public void onSuccess(LoginResult loginResult) { 
      Profile profile = Profile.getCurrentProfile(); 
      nextActivity(profile); 
     } 
     @Override 
     public void onCancel() {  } 
     @Override 
     public void onError(FacebookException e) {  } 
    }; 


    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     FacebookSdk.sdkInitialize(getApplicationContext()); 
     callbackManager = CallbackManager.Factory.create(); 
     accessTokenTracker = new AccessTokenTracker() { 
      @Override 
      protected void onCurrentAccessTokenChanged(AccessToken oldAccessToken, AccessToken currentAccessToken) { 

      } 
     }; 

     profileTracker = new ProfileTracker() { 
      @Override 
      protected void onCurrentProfileChanged(Profile oldProfile, Profile newProfile) { 
       nextActivity(newProfile); 
      } 
     }; 
     accessTokenTracker.startTracking(); 
     profileTracker.startTracking(); 
     LoginButton loginButton = (LoginButton)findViewById(R.id.login_button); 
     callback = new FacebookCallback<LoginResult>() { 
      @Override 
      public void onSuccess(LoginResult loginResult) { 
       AccessToken accessToken = loginResult.getAccessToken(); 
       Profile profile = Profile.getCurrentProfile(); 
       nextActivity(profile); 
       Toast.makeText(getApplicationContext(), "Logging in...", Toast.LENGTH_SHORT).show(); } 

      @Override 
      public void onCancel() { 
      } 

      @Override 
      public void onError(FacebookException e) { 
      } 
     }; 
     loginButton.setReadPermissions("user_friends"); 
     loginButton.registerCallback(callbackManager, callback); 
    } 

    @Override 
    protected void onResume() { 
     super.onResume(); 
     //Facebook login 
     Profile profile = Profile.getCurrentProfile(); 
     nextActivity(profile); 
    } 

    @Override 
    protected void onPause() { 

     super.onPause(); 
    } 

    protected void onStop() { 
     super.onStop(); 
     //Facebook login 
     accessTokenTracker.stopTracking(); 
     profileTracker.stopTracking(); 
    } 

    @Override 
    protected void onActivityResult(int requestCode, int responseCode, Intent intent) { 
     super.onActivityResult(requestCode, responseCode, intent); 
     //Facebook login 
     callbackManager.onActivityResult(requestCode, responseCode, intent); 

    } 

    private void nextActivity(Profile profile){ 
     if(profile != null){ 
      Intent main = new Intent(LoginActivity.this, MainActivity.class); 
      main.putExtra("name", profile.getFirstName()); 
      main.putExtra("surname", profile.getLastName()); 
      main.putExtra("imageUrl", profile.getProfilePictureUri(200,200).toString()); 
      startActivity(main); 
     } 
    } 
} 

エラーは次のとおりです：

08-06 21:58:45.079 16282-16282/com.example.mabdullahali.trenditch E/AndroidRuntime: FATAL EXCEPTION: main 
08-06 21:58:45.079 16282-16282/com.example.mabdullahali.trenditch E/AndroidRuntime: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.mabdullahali.trenditch/com.example.mabdullahali.trenditch.LoginActivity}: java.lang.NullPointerException 
08-06 21:58:45.079 16282-16282/com.example.mabdullahali.trenditch E/AndroidRuntime:  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2295) 
08-06 21:58:45.079 16282-16282/com.example.mabdullahali.trenditch E/AndroidRuntime:  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2349) 
08-06 21:58:45.079 16282-16282/com.example.mabdullahali.trenditch E/AndroidRuntime:  at android.app.ActivityThread.access$700(ActivityThread.java:159) 
08-06 21:58:45.079 16282-16282/com.example.mabdullahali.trenditch E/AndroidRuntime:  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1316) 
08-06 21:58:45.079 16282-16282/com.example.mabdullahali.trenditch E/AndroidRuntime:  at android.os.Handler.dispatchMessage(Handler.java:99) 
08-06 21:58:45.079 16282-16282/com.example.mabdullahali.trenditch E/AndroidRuntime:  at android.os.Looper.loop(Looper.java:176) 
08-06 21:58:45.079 16282-16282/com.example.mabdullahali.trenditch E/AndroidRuntime:  at android.app.ActivityThread.main(ActivityThread.java:5419) 
08-06 21:58:45.079 16282-16282/com.example.mabdullahali.trenditch E/AndroidRuntime:  at java.lang.reflect.Method.invokeNative(Native Method) 
08-06 21:58:45.079 16282-16282/com.example.mabdullahali.trenditch E/AndroidRuntime:  at java.lang.reflect.Method.invoke(Method.java:525) 
08-06 21:58:45.079 16282-16282/com.example.mabdullahali.trenditch E/AndroidRuntime:  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1046) 
08-06 21:58:45.079 16282-16282/com.example.mabdullahali.trenditch E/AndroidRuntime:  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:862) 
08-06 21:58:45.079 16282-16282/com.example.mabdullahali.trenditch E/AndroidRuntime:  at dalvik.system.NativeStart.main(Native Method) 
08-06 21:58:45.079 16282-16282/com.example.mabdullahali.trenditch E/AndroidRuntime: Caused by: java.lang.NullPointerException 
08-06 21:58:45.079 16282-16282/com.example.mabdullahali.trenditch E/AndroidRuntime:  at com.example.mabdullahali.trenditch.LoginActivity.onCreate(LoginActivity.java:79) 
08-06 21:58:45.079 16282-16282/com.example.mabdullahali.trenditch E/AndroidRuntime:  at android.app.Activity.performCreate(Activity.java:5372) 
08-06 21:58:45.079 16282-16282/com.example.mabdullahali.trenditch E/AndroidRuntime:  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1104) 
08-06 21:58:45.079 16282-16282/com.example.mabdullahali.trenditch E/AndroidRuntime:  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2257) 
08-06 21:58:45.079 16282-16282/com.example.mabdullahali.trenditch E/AndroidRuntime:  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2349)  
08-06 21:58:45.079 16282-16282/com.example.mabdullahali.trenditch E/AndroidRuntime:  at android.app.ActivityThread.access$700(ActivityThread.java:159)  
08-06 21:58:45.079 16282-16282/com.example.mabdullahali.trenditch E/AndroidRuntime:  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1316)  
08-06 21:58:45.079 16282-16282/com.example.mabdullahali.trenditch E/AndroidRuntime:  at android.os.Handler.dispatchMessage(Handler.java:99)  
08-06 21:58:45.079 16282-16282/com.example.mabdullahali.trenditch E/AndroidRuntime:  at android.os.Looper.loop(Looper.java:176)  
08-06 21:58:45.079 16282-16282/com.example.mabdullahali.trenditch E/AndroidRuntime:  at android.app.ActivityThread.main(ActivityThread.java:5419)  
08-06 21:58:45.079 16282-16282/com.example.mabdullahali.trenditch E/AndroidRuntime:  at java.lang.reflect.Method.invokeNative(Native Method)  
08-06 21:58:45.079 16282-16282/com.example.mabdullahali.trenditch E/AndroidRuntime:  at java.lang.reflect.Method.invoke(Method.java:525)  
08-06 21:58:45.079 16282-16282/com.example.mabdullahali.trenditch E/AndroidRuntime:  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1046)  
08-06 21:58:45.079 16282-16282/com.example.mabdullahali.trenditch E/AndroidRuntime:  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:862)  
08-06 21:58:45.079 16282-16282/com.example.mabdullahali.trenditch E/AndroidRuntime:  at dalvik.system.NativeStart.main(Native Method)  

Answer 1

あなたがマニフェストファイルにあなたの活動を宣言していない

は、これが私のloginActivityコードです。

新しいアクティビティクラスファイルを作成するたびに、それをマニフェストファイルに宣言する必要があります。

<activity 
     android:name="LoginActivity"/>