如何在空对象引用上调用虚拟方法java.lang.Stringorg.json.JSONObject.getString（java.lang.String）

Question

我正在使用Facebook登录我使用firebase的应用程序。当用户登录时，该应用程序应该从Facebook上获取诸如姓名、电子邮件、性别、位置、简历等信息。在我升级到AndroidStudio 2.2之前，它工作得很好。现在在更新之后，我得到了错误

尝试调用虚拟方法“java”。字符串组织。json。JSONObject。空对象引用上的getString（java.lang.String）”。

帐户保存到Firebase，但登录后应用程序崩溃。我不知道这是模拟器的茴香（Nexus 6 API 23），还是我的代码出了问题。

Logcat

10-27 08:23:07.965 15474-15474/com.rograb.workorderapp D/LOGIN DEBUG:facebook:onSuccess:com.facebook.login.LoginResult@47060b7
10-27 08:23:07.965 15474-15474/com.rograb.workorderapp D/LOGIN DEBUG: handleFacebookAccessToken:{AccessToken token:ACCESS_TOKEN_REMOVED permissions:[public_profile, contact_email, user_friends, user_likes, email, user_location]}
10-27 08:23:07.967 15474-15487/com.rograb.workorderapp W/DynamiteModule: Local module descriptor class for com.google.firebase.auth not found.
10-27 08:23:07.971 15474-16534/com.rograb.workorderapp V/FA: Activity resumed, time: 1301956
10-27 08:23:07.973 15474-15487/com.rograb.workorderapp W/DynamiteModule: Local module descriptor class for com.google.firebase.auth not found.
10-27 08:23:07.986 15474-15533/com.rograb.workorderapp E/Surface: getSlotFromBufferLocked: unknown buffer: 0xb2c3e080
10-27 08:23:08.366 15474-15474/com.rograb.workorderapp D/AndroidRuntime: Shutting down VM
10-27 08:23:08.366 15474-15474/com.rograb.workorderapp E/AndroidRuntime: FATAL EXCEPTION: main
                                                                     Process: com.rograb.workorderapp, PID: 15474
                                                                     java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String org.json.JSONObject.getString(java.lang.String)' on a null object reference
                                                                         at com.rograb.workorderapp.models.UserModel.fromJSON(UserModel.java:117)
                                                                         at com.rograb.workorderapp.activities.LoginActivity$2$1.onCompleted(LoginActivity.java:106)
                                                                         at com.facebook.GraphRequest$1.onCompleted(GraphRequest.java:304)
                                                                         at com.facebook.GraphRequest$5.run(GraphRequest.java:1383)
                                                                         at android.os.Handler.handleCallback(Handler.java:739)
                                                                         at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                         at android.os.Looper.loop(Looper.java:148)
                                                                         at android.app.ActivityThread.main(ActivityThread.java:5417)
                                                                         at java.lang.reflect.Method.invoke(Native Method)
                                                                         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                                                                         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
10-27 08:23:11.904 15474-15474/com.rograb.workorderapp I/Process: Sending signal. PID: 15474 SIG: 9

用户模型

public class UserModel {

private String id;
private String name;
private String email;
private String gender;
private String locationId;
private String locationName;
private String bio;
private String languages;
private ArrayList<TripModel> favorites = new ArrayList<>();

private HashMap<String, Object> timestampJoined;

public UserModel() {
}

public UserModel(String name, String email, HashMap<String, Object> timestampJoined) {
    this.name = name;
    this.email = email;
    this.timestampJoined = timestampJoined;
}

public String getId() {
    return id;
}

public void setId(String id) {
    this.id = id;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public String getEmail() {
    return email;
}

public void setEmail(String email) {
    this.email = email;
}

public String getGender() {
    return gender;
}

public void setGender(String gender) {
    this.gender = gender;
}

public String getLocationId() {
    return locationId;
}

public void setLocationId(String locationId) {
    this.locationId = locationId;
}

public String getLocationName() {
    return locationName;
}

public void setLocationName(String locationName) {
    this.locationName = locationName;
}

public String getBio() {
    return bio;
}

public void setBio(String bio) {
    this.bio = bio;
}

public String getLanguages() {
    return languages;
}

public void setLanguages(String languages) {
    this.languages = languages;
}

public HashMap<String, Object> getTimestampJoined() {
    return timestampJoined;
}

public void setTimestampJoined(HashMap<String, Object> timestampJoined) {
    this.timestampJoined = timestampJoined;
}

public ArrayList<TripModel> getFavorites() {
    return favorites;
}

public void setFavorites(ArrayList<TripModel> favorites) {
    this.favorites = favorites;
}

public static UserModel fromJSON(JSONObject jsonObject){
    UserModel user = new UserModel();

    try {
        user.id = jsonObject.getString("id");
        user.name = jsonObject.getString("name");
        user.email = jsonObject.getString("email");
        user.gender = jsonObject.getString("gender");
        user.locationId = jsonObject.getJSONObject("location").getString("id");
        user.locationName = jsonObject.getJSONObject("location").getString("name");
        user.languages = "";

    } catch (JSONException e) {
        e.printStackTrace();
    }

    return user;
}
}

登陆界面

public class LoginActivity extends AppCompatActivity {

private static final String TAG = "LOGIN DEBUG";
@BindView(R.id.btnFacebookLogin)
LoginButton btnFacebookLogin;

CallbackManager callbackManager;
private FirebaseAuth mAuth;
private FirebaseAuth.AuthStateListener mAuthListener;
UserModel userModel = new UserModel();

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_login);
    ButterKnife.bind(this);

    final WorkOrderApplication app = (WorkOrderApplication) getApplicationContext();

    // Initialize Firebase Auth
    mAuth = FirebaseAuth.getInstance();
    mAuthListener = new FirebaseAuth.AuthStateListener() {
        @Override
        public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) {
            FirebaseUser user = firebaseAuth.getCurrentUser();
            if (user != null) {
                // User is signed in
                Log.d(TAG, "onAuthStateChanged:signed_in:" + user.getUid());

                if (user.getEmail() == null || user.getEmail().equals(""))
                    user.updateEmail(userModel.getEmail());

                if (user.getUid() != null) {
                    setAuthenticatedUserFacebook(firebaseAuth);
                    onLoginSuccess();
                }

            } else {
                // User is signed out
                Log.d(TAG, "onAuthStateChanged:signed_out");
            }
        }
    };


    // Initialize Facebook Login button
    callbackManager = CallbackManager.Factory.create();

    btnFacebookLogin.setReadPermissions(Arrays.asList("public_profile", "email", "user_location", "user_friends", "user_likes"));
    btnFacebookLogin.registerCallback(callbackManager, new FacebookCallback<LoginResult>() {
        @Override
        public void onSuccess(LoginResult loginResult) {
            Log.d(TAG, "facebook:onSuccess:" + loginResult);

            handleFacebookAccessToken(loginResult.getAccessToken());

            // App code
            GraphRequest request = GraphRequest.newMeRequest(
                    loginResult.getAccessToken(),
                    new GraphRequest.GraphJSONObjectCallback() {
                        @Override
                        public void onCompleted(JSONObject object, GraphResponse response) {

                            userModel = UserModel.fromJSON(object);
                            app.setUserInfo(userModel);

                        }
                    });

            Bundle parameters = new Bundle();
            parameters.putString("fields", "id,name,email,gender,location,bio,languages");
            request.setParameters(parameters);
            request.executeAsync();

        }

        @Override
        public void onCancel() {
            Log.d(TAG, "facebook:onCancel");

        }

        @Override
        public void onError(FacebookException error) {
            Log.d(TAG, "facebook:onError", error);
        }
    });

}

private void setAuthenticatedUserFacebook(FirebaseAuth firebaseAuth) {

    final String userEncondedEmail = Utilities.encodeEmail(firebaseAuth.getCurrentUser().getEmail());
    String userName = firebaseAuth.getCurrentUser().getDisplayName();

    HashMap<String, Object> timestampJoined = new HashMap<>();
    timestampJoined.put(Constants.FIREBASE_PROPERTY_TIMESTAMP, ServerValue.TIMESTAMP);

    final WorkOrderApplication app = (WorkOrderApplication) getApplicationContext();

    //Save user in firebase
    final UserModel user = new UserModel(userName, userEncondedEmail, timestampJoined);

    app.getUsersReference().child(userEncondedEmail).addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            if (dataSnapshot.getValue() == null) {
                app.getUsersReference().child(userEncondedEmail).setValue(user);
            }
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {
        }
    });
}

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

@Override
public void onStart() {
    super.onStart();
    mAuth.addAuthStateListener(mAuthListener);
}

@Override
public void onStop() {
    super.onStop();
    if (mAuthListener != null) {
        mAuth.removeAuthStateListener(mAuthListener);
    }
}

public void onLoginSuccess() {


    Intent i = new Intent(this, JobListActivity.class);
    i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP
            | Intent.FLAG_ACTIVITY_NEW_TASK
            | Intent.FLAG_ACTIVITY_CLEAR_TASK);
    startActivity(i);
    finish();

}

private void handleFacebookAccessToken(AccessToken token) {
    Log.d(TAG, "handleFacebookAccessToken:" + token);

    AuthCredential credential = FacebookAuthProvider.getCredential(token.getToken());
    mAuth.signInWithCredential(credential)
            .addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
                @Override
                public void onComplete(@NonNull Task<AuthResult> task) {
                    Log.d(TAG, "signInWithCredential:onComplete:" + task.isSuccessful());

                    // If sign in fails, display a message to the user. If sign in succeeds
                    // the auth state listener will be notified and logic to handle the
                    // signed in user can be handled in the listener.
                    if (!task.isSuccessful()) {
                        Log.w(TAG, "signInWithCredential", task.getException());
                        Toast.makeText(LoginActivity.this, "Authentication failed.",
                                Toast.LENGTH_SHORT).show();
                    } else {
                        onLoginSuccess();
                    }


                }
            });
}

}

建筑格拉德尔

android {
compileSdkVersion 24
buildToolsVersion "24.0.0"
defaultConfig {
    applicationId "com.rograb.workorderapp"
    minSdkVersion 16
    targetSdkVersion 24
    versionCode 1
    versionName "1.0"
    testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    externalNativeBuild {
        cmake {
            cppFlags ""
        }
    }
}
buildTypes {
    release {
        minifyEnabled false
        proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
    }
}
externalNativeBuild {
    cmake {
        path "CMakeLists.txt"
    }
}
}
repositories {
mavenCentral()
}

dependencies {
compile fileTree(dir: 'libs', include: ['*.jar'])
androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
    exclude group: 'com.android.support', module: 'support-annotations'
})
compile 'com.android.support:appcompat-v7:24.0.0'
testCompile 'junit:junit:4.12'
apt 'com.jakewharton:butterknife-compiler:8.2.1'

apt 'org.parceler:parceler:1.1.1'
compile 'com.android.support:appcompat-v7:24.2.0'
compile 'com.android.support:design:24.2.0'
compile 'com.android.support:cardview-v7:24.2.0'
compile 'com.android.support:recyclerview-v7:24.2.0'
compile 'com.squareup.picasso:picasso:2.5.2'
compile 'com.google.firebase:firebase-auth:9.4.0'
compile 'com.facebook.android:facebook-android-sdk:[4,5)'
compile 'com.jakewharton:butterknife:8.2.1'
compile 'org.parceler:parceler-api:1.1.1'
compile 'com.google.firebase:firebase-database:9.4.0'
compile 'com.firebaseui:firebase-ui-database:0.5.1'
compile 'com.google.android.gms:play-services-location:9.4.0'
compile 'com.google.android.gms:play-services-maps:9.4.0'
compile 'com.google.android.gms:play-services-places:9.4.0'
compile 'com.firebase:geofire-android:2.1.0'
compile 'com.github.qiugang:EditTag:v1.2.3'
compile 'com.astuetz:pagerslidingtabstrip:1.0.1'
compile 'com.android.support:support-v4:24.2.0'
}
apply plugin: 'com.google.gms.google-services'

配置文件

public class ProfileActivity extends AppCompatActivity implements OnMapReadyCallback {

WorkOrderApplication app;
private GoogleMap mMap;

@BindView(R.id.ivProfile)
ProfilePictureView ivProfile;
@BindView(R.id.tvBio)
TextView tvBio;
@BindView(R.id.tvEmail)
TextView tvEmail;
@BindView(R.id.app_bar)
AppBarLayout appBar;
@BindView(R.id.toolbar)
Toolbar toolbar;
@BindView(R.id.tvUserName)
TextView tvUserName;
@BindView(R.id.tvLocationName)
TextView tvLocationName;
@BindView(R.id.toolbar_layout)
CollapsingToolbarLayout collapsingToolbarLayout;
@BindView(R.id.tvLanguages)
TextView tvLanguages;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_profile);
    ButterKnife.bind(this);

    setSupportActionBar(toolbar);

    SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map);
    mapFragment.getMapAsync(this);

    app = (WorkOrderApplication) getApplicationContext();

}

@Override
public void onBackPressed() {
    finish();
    overridePendingTransition(R.anim.left_in, R.anim.right_out);
}

@Override
public void onMapReady(GoogleMap googleMap) {
    mMap = googleMap;
    setUserInformation();

}

private void setUserInformation() {

    UserModel user = app.getUserInfo();

    ivProfile.setProfileId(user.getId());
    tvUserName.setText(user.getName());
    tvLocationName.setText(user.getLocationName());

    tvBio.setText(user.getBio());
    if (user.getBio().equals(Constants.EMPTY_STRING)) {
        tvBio.setVisibility(View.GONE);
    }
    tvEmail.setText(user.getEmail());
    //tvLanguages.setText(user.getLanguages());

    //Set marker in User location
    LatLng userLatLong = getUserLatLong(user.getLocationName());
    mMap.addMarker(new MarkerOptions()
            .position(userLatLong)
            .icon(BitmapDescriptorFactory.fromBitmap(Utilities.writeTextOnDrawable(this, R.drawable.user_marker, "")))
            .title(user.getLocationName()));

    mMap.moveCamera(CameraUpdateFactory.newLatLng(userLatLong));
    mMap.animateCamera(CameraUpdateFactory.zoomTo(5.0f));

    //Collapsing Toolbar options
    collapsingToolbarLayout.setExpandedTitleColor(Color.TRANSPARENT);
    //collapsingToolbarLayout.setTitle(user.getName());
    collapsingToolbarLayout.setTitle(" ");
    CoordinatorLayout.LayoutParams params = (CoordinatorLayout.LayoutParams) appBar.getLayoutParams();
    AppBarLayout.Behavior behavior = new AppBarLayout.Behavior();
    behavior.setDragCallback(new AppBarLayout.Behavior.DragCallback() {
        @Override
        public boolean canDrag(@NonNull AppBarLayout appBarLayout) {
            return false;
        }
    });
    params.setBehavior(behavior);

}

private LatLng getUserLatLong(String locationName) {

    LatLng userLatLong = null;
    if (Geocoder.isPresent()) {
        try {
            Geocoder gc = new Geocoder(this);
            List<Address> addresses = gc.getFromLocationName(locationName, 1); // get the found Address Objects

            for (Address a : addresses) {
                if (a.hasLatitude() && a.hasLongitude()) {
                    userLatLong = new LatLng(a.getLatitude(), a.getLongitude());
                }
            }
        } catch (IOException e) {
            Log.e("Geocoder Error", e.toString());
        }
    }

    return userLatLong;
}

}

Answer 1

问题是Facebook更新了他们的权限，我被要求提交审查以获得user_location。这就是为什么它开始工作，然后突然停止。

Answer 2

异常表示您正试图取消对空值的引用。

根据代码判断，我认为您的JSON对象中没有“位置”，因此此行失败：

jsonObject.getJSONObject("location").getString("id");

stacktrace在这里非常有用。

at com.rograb.workorderapp.models.UserModel.fromJSON(UserModel.java:117)

这告诉你你的代码在第117行中断了。

大多数编辑器都有“跳转到行”功能，即行编号。在Eclipse中，可以使用Ctrl-L。

这里有一个有趣的提示：

在Eclipse中，您可以打开一个新的“Java堆栈跟踪”控制台。从日志中复制堆栈跟踪，并将其粘贴到Java堆栈跟踪控制台中。

然后，您只需单击stacktrace文本，它就会直接将您带到有问题的行！