嘗試調用另一個類的函數時發生NullPoint錯誤

-3

我正在嘗試從我的reg.java類調用函數registerGCM();到類MainActivity.java。嘗試調用另一個類的函數時發生NullPoint錯誤

當我使用功能從reg.java活動的應用程式運作得很好，但每當我把它從MainActivity裏面我得到這個錯誤

07-28 13:38:38.540 24434-24434/com.example.kmi_dev.fbloginsample E/AndroidRuntime﹕ FATAL EXCEPTION: main 
    Process: com.example.kmi_dev.fbloginsample, PID: 24434 
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.kmi_dev.fbloginsample/com.example.kmi_dev.fbloginsample.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String com.example.kmi_dev.fbloginsample.reg.registerGCM()' on a null object reference 
      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2325) 
      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2390) 
      at android.app.ActivityThread.access$800(ActivityThread.java:151) 
      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303) 
      at android.os.Handler.dispatchMessage(Handler.java:102) 
      at android.os.Looper.loop(Looper.java:135) 
      at android.app.ActivityThread.main(ActivityThread.java:5257) 
      at java.lang.reflect.Method.invoke(Native Method) 
      at java.lang.reflect.Method.invoke(Method.java:372) 
      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903) 
      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698) 
    Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String com.example.kmi_dev.fbloginsample.reg.registerGCM()' on a null object reference 
      at com.example.kmi_dev.fbloginsample.MainActivity.onCreate(MainActivity.java:158) 
      at android.app.Activity.performCreate(Activity.java:5990) 
      at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106) 
      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2278) 
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2390) 
            at android.app.ActivityThread.access$800(ActivityThread.java:151) 
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303) 
            at android.os.Handler.dispatchMessage(Handler.java:102) 
            at android.os.Looper.loop(Looper.java:135) 
            at android.app.ActivityThread.main(ActivityThread.java:5257) 
            at java.lang.reflect.Method.invoke(Native Method) 
            at java.lang.reflect.Method.invoke(Method.java:372) 
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903) 
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

內容，其中呼叫正在取得在MainActivity內

內容的

public class MainActivity extends Activity { 
    private static final String TAG = "MainActivity"; 
    private static final String MYPREFERENCES = "myPref"; 
    private CallbackManager callbackManager; 
    private LoginButton fbLoginButton; 
    private Button login; 
    . 
    . 
    . 
    . 
    GPSTracker gps; 
    reg GCM_REG; 


    // flag for Internet connection status 
    Boolean isInternetPresent = false; 

    // Connection detector class 
    ConnectionDetector cd; 
    SessionManager session; 
    . 
    . 
    String gcmId; 
    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 


     //get global variable class 
     final GlobalClass globalVariable = (GlobalClass) getApplicationContext(); 
     gcmId = GCM_REG.registerGCM();

registerGCM()

public String registerGCM() { 
     gcm = GoogleCloudMessaging.getInstance(this); 
     regId = getRegistrationId(context); 

     if (TextUtils.isEmpty(regId)) { 
      registerInBackground(); 
      Log.d("MainActivity", 
        "registerGCM - successfully registered with GCM server - regId: " 
          + regId); 
     } else { 
      Toast.makeText(getApplicationContext(), 
        "RegId already available. RegId: " + regId, 
        Toast.LENGTH_LONG).show(); 
     } 
     final GlobalClass globalVariable = (GlobalClass) getApplicationContext(); 
     globalVariable.setGcmRegId(regId); 
     return regId; 
    } 
    public String getRegistrationId(Context context) { 
     final SharedPreferences prefs = getSharedPreferences(reg.class.getSimpleName(), Context.MODE_PRIVATE); 
     String registrationId = prefs.getString(REG_ID, ""); 
     if (registrationId.isEmpty()) { 
      Log.i(TAG, "Registration not found."); 
      return ""; 
     } 
     int registeredVersion = prefs.getInt(APP_VERSION, Integer.MIN_VALUE); 
     int currentVersion = getAppVersion(context); 
     if (registeredVersion != currentVersion) { 
      Log.i(TAG, "App version changed."); 
      return ""; 
     } 
     return registrationId; 
    }

任何想法爲什麼我無法調用此函數？

來源

2015-07-28 Rick Roy

NullPointerException：http://stackoverflow.com/questions/218384/what-is-a-null-pointer-exception-and-how-do-i-fix-it – dotvav

對象GCM_REG沒有初始化我猜。請檢查你的代碼。 –

你永遠不會初始化GCM_REG。這就是爲什麼你得到一個NullPointerException。

來源

2015-07-28 08:18:24 Jens

嘗試調用另一個類的函數時發生NullPoint錯誤

回答

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