android - 为什么我不能在 FacebookCallback 之外使用我的 ArrayList 变量

Question

您好，我正在尝试实现 Facebook 登录和获取好友列表。我正在将我 friend 的姓名和个人资料图片网址存储到 ArrayList<TaggedFriends> 中TaggedFriends 类将在何处设置和获取方法。

我现在在名为 MainFragment 的 Fragment 类中工作。在这里，我将值存储到 FacebookCallback session 中的 taggableFriends 变量中。但我无法访问它到任何其他地方我试图将它存储到 SharedPreferences 中，但是当我尝试存储时，它返回空值。

这是我的MainFragment的完整代码

public class MainFragment extends Fragment {
    String email, tag = "MainFragment kbt";
    ArrayList<TaggableFriends> taggableFriends = new ArrayList<TaggableFriends>();
    ArrayList<TaggableFriends> testing = new ArrayList<>();
    MainActivity mainActivity ;

    private CallbackManager callbackManager;
    private TextView textView;

    private AccessTokenTracker accessTokenTracker;
    private ProfileTracker profileTracker;


    private FacebookCallback<LoginResult> callback = new FacebookCallback<LoginResult>() {
        @Override
        public void onSuccess(LoginResult loginResult) {
            AccessToken accessToken = loginResult.getAccessToken();
            Profile profile = Profile.getCurrentProfile();        
            new GraphRequest(
                    AccessToken.getCurrentAccessToken(),
                    "/me/taggable_friends",
                    null,
                    HttpMethod.GET,
                    new GraphRequest.Callback() {
                        public void onCompleted(GraphResponse response) {
                            //    handle the result
                            Log.d("RESPONSE KBT", response.getRawResponse());
                            try {

                                JSONObject obj = new JSONObject(response.getRawResponse());
                                JSONArray array = obj.getJSONArray("data");
                                for (int i = 0; i < array.length(); i++) {
                                    JSONObject indi = array.getJSONObject(i);
                                    JSONObject pic = indi.getJSONObject("picture");
                                    JSONObject data = pic.getJSONObject("data");
                                    String name = indi.getString("name");
                                    String url = data.getString("url");
                                    TaggableFriends tf = new TaggableFriends(name, url);
                                    taggableFriends.add(tf);
                                    Log.d("NAME", tf.getName());
                                    Log.d("SIZE", ":"+taggableFriends.size());


                                }
                            } catch (JSONException e) {
                                e.printStackTrace();
                            }
                            Log.d(tag,"SECOND SIZE"+taggableFriends.size());
                           //
                        }
                    }
            ).executeAsync();           

            JSONArray mJSONArray = new JSONArray(taggableFriends);
            SharedPreferences mPrefs = getActivity().getSharedPreferences("My_File",Context.MODE_PRIVATE);
            SharedPreferences.Editor mEditor = mPrefs.edit();
            mEditor.putString("myKey", mJSONArray.toString());
            Log.d(tag,"STRING JSON : "+mJSONArray.toString());
            mEditor.commit();
        displayMessage(profile);
        }

        @Override
        public void onCancel() {

        }

        @Override
        public void onError(FacebookException e) {

        }
    };


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

        FacebookSdk.sdkInitialize(getActivity().getApplicationContext());

        callbackManager = CallbackManager.Factory.create();

        accessTokenTracker = new AccessTokenTracker() {
            @Override
            protected void onCurrentAccessTokenChanged(AccessToken oldToken, AccessToken newToken) {

            }
        };

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

        accessTokenTracker.startTracking();
        profileTracker.startTracking();
    }

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

    @Override
    public void onViewCreated(View view, Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        LoginButton loginButton = (LoginButton) view.findViewById(R.id.login_button);
        textView = (TextView) view.findViewById(R.id.textView);

        // loginButton.setReadPermissions("user_friends");
        loginButton.setReadPermissions(Arrays.asList("email", "user_friends", "read_custom_friendlists"));
        // loginButton.setReadPermissions(Arrays.asList("public_profile", "user_friends"));
        loginButton.setFragment(this);
        loginButton.registerCallback(callbackManager, callback);
        Log.d(tag,"taggable "+taggableFriends.size());
      //  if(taggableFriends.size()!=0)


    }

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

    }

    private void displayMessage(Profile profile) {
        if (profile != null) {
            textView.setText(profile.getName());

        }
    }
}

请注意 FacebookCallBack --> onSuccess() 方法。我在那里存储变量 taggedFriends

的值

紧接着我将 taggedFriends 存储到 SharedPreferences 中。但是在那个地方，taggedFriends 变量为空。它不包含任何内容。我检查了 Logcat。

在 onSuccess() 方法内部，它的值在那里，当我使用该方法时，它为空。有什么问题？

Answer 1

图形 API 调用是异步执行的，即在单独的线程中执行。看起来当您尝试将值存储在 SharedPreferences 中时，异步调用尚未完成并且您得到 null。尝试将存储在 SharedPreferences 部分移动到 onCompleted 方法中，在将它添加到 ArrayList 之后立即进行。