Facebook 按钮片段未打开和终止应用程序

Question

我创建了一个带有 facebook 按钮的片段。它工作了一段时间，现在当我尝试使用导航应用程序抽屉打开片段时，应用程序崩溃了。

下面是堆栈跟踪：

E/AndroidRuntime: FATAL EXCEPTION: main Process: com.myclass.myapp, PID: 3526 java.lang.NullPointerException: Attempt to invoke virtual method 'void com.facebook.AccessTokenTracker.startTracking()' on a null object reference at com.myclass.myapp.FacebookLogin.onCreate(FacebookLogin.java:82) at android.support.v4.app.Fragment.performCreate(Fragment.java:2177) at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1244) at android.support.v4.app.FragmentTransition.addToFirstInLastOut(FragmentTransition.java:1080) at android.support.v4.app.FragmentTransition.calculateFragments(FragmentTransition.java:971) at android.support.v4.app.FragmentTransition.startTransitions(FragmentTransition.java:95) at android.support.v4.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2143) at android.support.v4.app.FragmentManagerImpl.optimizeAndExecuteOps(FragmentManager.java:2098) at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:2008) at android.support.v4.app.FragmentManagerImpl.run(FragmentManager.java:710) at android.os.Handler.handleCallback(Handler.java:751) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:154) at android.app.ActivityThread.main(ActivityThread.java:6077) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755) Application terminated.

片段代码class:

    public class FacebookLogin extends Fragment {

    //initialize WebView
    private TextView mTextDetails;
    private CallbackManager mCallbackManager;
    private AccessTokenTracker mTokenTracker;
    private ProfileTracker mProfileTracker;

    private FacebookCallback<LoginResult> mCallback=new FacebookCallback<LoginResult>() {
        @Override
        public void onSuccess(LoginResult loginResult) {

            AccessToken accessToken = loginResult.getAccessToken();
            Profile profile = Profile.getCurrentProfile();
            displayWelcomeMessage(profile);
        }

        @Override
        public void onCancel() {

        }

        @Override
        public void onError(FacebookException error) {

        }
    };

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

            }
        };

        ProfileTracker profileTracker=new ProfileTracker() {
            @Override
            protected void onCurrentProfileChanged(Profile oldProfile, Profile currentProfile) {
                displayWelcomeMessage(currentProfile);
            }
        };

        mTokenTracker.startTracking();
        mProfileTracker.startTracking();
  }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(R.layout.facebook_login, container, false);
   }

   private void displayWelcomeMessage(Profile profile){
        if (profile != null){
            mTextDetails.setText(profile.getName());
        }

    }



    @Override
    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        LoginButton loginButton = (LoginButton) view.findViewById(R.id.login_button);
        loginButton.setReadPermissions("user_friends");
        loginButton.setFragment(this);
        loginButton.registerCallback(mCallbackManager,mCallback);

        mTextDetails = (TextView)view.findViewById(R.id.text_details);
    }

    @Override
    public void onResume() {
        super.onResume();
        Profile profile=Profile.getCurrentProfile();
        displayWelcomeMessage(profile);
    }

    @Override
    public void onStop(){
        super.onStop();
        mTokenTracker.stopTracking();
        mProfileTracker.stopTracking();
    }

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

Answer 1

您没有在 onCreate()

中初始化 mTokenTracker

 mTokenTracker = new AccessTokenTracker() {
        @Override
        protected void onCurrentAccessTokenChanged(AccessToken oldToken, AccessToken newToken) {
            updateWithToken(newToken);
        }
    };
    mTokenTracker.startTracking();

还有你的mProfileTracker没有初始化

mProfileTracker = new ProfileTracker() {
                                    @Override
                                    protected void onCurrentProfileChanged(com.facebook.Profile profile_old, com.facebook.Profile profile_new) {
                                        // profile2 is the new profile
                                        profile = profile_new;
                                        mProfileTracker.stopTracking();
                                    }
                                };
                                mProfileTracker.startTracking();