如何在空對象引用上調用虛擬方法'java.lang.String org.json.JSONObject.getString（java.lang.String）'

我正在使用Facebook登錄爲我的應用程序使用Firebase。當用戶登錄時，應用程序應該從Facebook上獲取信息，例如姓名，電子郵件，性別，地點，生物等等。在我更新到Android Studio 2.2之前，這工作得很好。更新後，我得到錯誤如何在空對象引用上調用虛擬方法'java.lang.String org.json.JSONObject.getString（java.lang.String）'

嘗試在空對象引用上調用虛擬方法'java.lang.String org.json.JSONObject.getString（java.lang.String）'。

該帳戶被保存到firebase，但登錄後應用程序崩潰。我不知道這是模擬器（Nexus 6 API 23）的大茴香，還是發生在我的代碼上。

logcat的

10-27 08:23:07.965 15474-15474/com.rograb.workorderapp D/LOGIN DEBUG:facebook:onSuccess:[email protected] 
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

的usermodel

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; 
} 
}

LoginActivity

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(); 
        } 


       } 
      }); 
} 

}

的build.gradle

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'

配置文件活動

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; 
} 

}

來源

2016-10-27 Evan Goff

可能重複[什麼是NullPointerException，以及如何解決它？]（http://stackoverflow.com/questions/218384/what-is-a-nullpointerexception-and-how-doi-i-fix - 它） –

檢查你的錯誤，它說刪除授權令牌。這意味着您忘記在Firebase中處理您的應用。 –

是的，我很尷尬地說，但我忘了將重定向URI添加到FB設置。我解決了這個問題，但我仍然得到相同的錯誤。我是firebase的新手。這可能是問題嗎？ –

該異常表明您試圖取消引用null的內容。

的代碼來看，我會想象它是在它的JSON對象不具有「位置」，所以這行失敗：

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

堆棧跟蹤是非常有用的在這裏。

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

這告訴你你的代碼在行打破117

大多數編輯有「跳轉到行」功能，或行號。在Eclipse中，您可以使用Ctrl-L。

這裏有一個有趣的提示：

在Eclipse中，你可以打開一個新的「Java堆棧跟蹤」控制檯。從日誌中複製堆棧跟蹤，並將其粘貼到Java堆棧跟蹤控制檯中。

然後，您只需點擊堆棧跟蹤文本，它會直接進入違規行！

來源

2016-10-27 14:37:41 Jamie

添加ProfileActivity，所有的FB信息的使用。我不明白爲什麼它以前對我有效，但現在不行。 –

我建議，當你要創建JSON對象傳入fromJson時，你應該打印出字符串或將它記錄到一個文件中，這樣你就可以看到缺少的東西。 – Jamie

它看起來像你的輸入JSON字符串{「rules」：{「.read」：「auth！= null」，「.write」：「auth！= null」}}作爲你的輸入JSON字符串。這絕對沒有身份證或位置。調用jsonObject.getJSONObject（「location」）將返回'null'，因爲該字符串中沒有位置。 – Jamie

問題是Facebook更新了他們的權限，我被要求提交審查才能獲得user_location。這是給我的AccessToken令牌：ACCESS_TOKEN_REMOVED錯誤。這就是爲什麼它開始工作，然後停下來的地方。

來源

2016-10-28 14:25:08

如何在空對象引用上調用虛擬方法'java.lang.String org.json.JSONObject.getString（java.lang.String）'

回答

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