在callbackmanager上獲取空指針異常

Question

我正在使用facebook SDK。 在記錄日志時，我得到了一個nullpointer異常，

 LoginButton loginButton;
    CallbackManager callbackManager;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        callbackManager = CallbackManager.Factory.create();
        FacebookSdk.sdkInitialize(getApplicationContext());

        setContentView(R.layout.activity_main);
        loginButton = (LoginButton)findViewById(R.id.login_button);
        List<String> permissionNeeds = Arrays.asList("user_photos", "email", "user_birthday", "public_profile");
        loginButton.setReadPermissions(permissionNeeds);
        loginButton.registerCallback(callbackManager, new FacebookCallback<LoginResult>()
        {
            @Override
            public void onSuccess(LoginResult loginResult)
            {
                System.out.println("onSuccess");
            }

            @Override
            public void onCancel()
            {
                System.out.println("onCancel");
            }

            @Override
            public void onError(FacebookException exception)
            {
                Log.v("LoginActivity", exception.getCause().toString());
            }
        });



    }


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

錯誤是由第二行中的onActivityResult方法callbackManager.onActivityResult（requestCode，resultCode，data）;引發的。

堆棧跟蹤的一部分：

06-20 14:07:52.253  21310-21310/com.itspirits.fbchatdownloader E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.itspirits.fbchatdownloader, PID: 21310
java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=64206, result=-1, data=Intent { (has extras) }} to activity {com.itspirits.fbchatdownloader/com.itspirits.fbchatdownloader.MainActivity}: java.lang.NullPointerException
        at android.app.ActivityThread.deliverResults(ActivityThread.java:3365)
        at android.app.ActivityThread.handleSendResult(ActivityThread.java:3408)
        at android.app.ActivityThread.access$1300(ActivityThread.java:135)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1244)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:136)
        at android.app.ActivityThread.main(ActivityThread.java:5017)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
        at dalvik.system.NativeStart.main(Native Method)
 Caused by: java.lang.NullPointerException
        at com.itspirits.fbchatdownloader.MainActivity$1.onError(MainActivity.java:53)
        at com.facebook.login.LoginManager.finishLogin(LoginManager.java:507)
        at com.facebook.login.LoginManager.onActivityResult(LoginManager.java:192)
        at com.facebook.login.LoginManager$1.onActivityResult(LoginManager.java:140)
        at com.facebook.internal.CallbackManagerImpl.onActivityResult(CallbackManagerImpl.java:82)
        at com.itspirits.fbchatdownloader.MainActivity.onActivityResult(MainActivity.java:69)
        at android.app.Activity.dispatchActivityResult(Activity.java:5423)
        at android.app.ActivityThread.deliverResults(ActivityThread.java:3361)
            at android.app.ActivityThread.handleSendResult(ActivityThread.java:3408)
            at android.app.ActivityThread.access$1300(ActivityThread.java:135)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1244)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5017)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
            at dalvik.system.NativeStart.main(Native Method)

Answer 1

callbackManager是否為null？ 數據為空嗎？ （不太可能）

您可以進行一些簡單的調試，例如在使用變量之前先打印變量，以了解一下什么以及何時為空:-)

Answer 2

這是我用於Facebook登錄的代碼。

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

    FacebookSdk.sdkInitialize(getApplicationContext());
    mCallbackManager = CallbackManager.Factory.create();

    setContentView(R.layout.activity_login);

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

    loginButton.setReadPermissions(Arrays.asList("public_profile, email, user_birthday, user_photos, user_friends"));
    loginButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            loginButton.registerCallback(mCallbackManager, new FacebookCallback<LoginResult>() {

                private ProfileTracker mProfileTracker;

                @Override
                public void onSuccess(final LoginResult loginResult) {
                    loginButton.setVisibility(View.INVISIBLE);
                    mProfileTracker = new ProfileTracker() {
                        @Override
                        protected void onCurrentProfileChanged(Profile profile1, Profile profile) {

                            final String userId = loginResult.getAccessToken().getUserId();

                            String profileImgUrl = "https://graph.facebook.com/" + userId + "/picture?type=large";
                            Log.d("Facebook ", "userId : " + userId);
                            final String token = loginResult.getAccessToken().getToken();
                            Log.d("Facebooklog ", "Token " + token);
                            if (profile == null) return;
                            String name = profile.getName();
                        }
                    };
                    mProfileTracker.startTracking();
                }

                @Override
                public void onCancel() {
                    Log.d("facebook - onCancel", "cancelled");
                }

                @Override
                public void onError(FacebookException e) {
                    Log.d("facebook - onError", e.getMessage());
                }
            });
        }
    });
}

希望能幫助到你