savedInstanceState捆綁包中的NullPointerException

Question

當我的代碼嘗試訪問由Activity類的onSaveInstanceState方法創建的鍵/值對中的值時，出現NullPointerException。

我設置了斷點，實際上我知道Bundle不是null，它包含對我的鍵/值的引用。 我不明白為什么會收到此運行時錯誤。 這是我的onSaveInstanceState代碼

@Override
protected void onSaveInstanceState(Bundle outState) {

    int mPoints = winCount;
    int hPoints = loseCount;
    String reTextView = resultsTextView.getText().toString();
    String pTextView = pointsTextView.getText().toString();
    String roTextView = rollTextView.getText().toString();

    outState.putInt("MY_POINTS", mPoints);
    outState.putInt("HOUSE_POINTS", hPoints);
    outState.putString("RESULTS", reTextView);
    outState.putString("POINTS", pTextView);
    outState.putString("ROLL", roTextView);

    super.onSaveInstanceState(outState);
}

這是我的代碼來還原onCreate方法的狀態

// check if app just started or is being restored from memory
      if ( savedInstanceState == null ) // the app just started running
      {
         winCount = 0; 
         loseCount = 0; 
      } 
      else 
      {
         winCount = savedInstanceState.getInt("MY_POINTS");
         loseCount = savedInstanceState.getInt("HOUSE_POINTS");

         resultsTextView.setText(String.valueOf(savedInstanceState.getString("RESULTS")));
         pointsTextView.setText(String.valueOf(savedInstanceState.getString("POINTS")));
         rollTextView.setText(String.valueOf(savedInstanceState.getString("ROLL")));
      } 

我在以resultsTextView.setText ...開頭的行上收到運行時錯誤，這是在調試模式下從斷點檢索的saveInstanceState Bundle的內容

 Bundle[{RESULTS=Roll Again, MY_POINTS=2, POINTS=Your Point is 8,
 HOUSE_POINTS=2,
 android:viewHierarchyState=Bundle[{android:Panels=android.util.SparseArray@421c5560,
 android:views=android.util.SparseArray@421c5358,
 android:ActionBar=android.util.SparseArray@421c57f8}], ROLL=You Rolled
 Easy Four}]

如您所見，我所有的字符串都有一個值，有趣的是，我沒有在int變量（winCount和LostCount）上遇到NullPointerException運行時錯誤，但是我在字符串值處得到了它。 感謝您的幫助。

更新：這是來自日志貓的整個錯誤日志，我在第68行（在onCreat（）的else塊中）有resultsTextView.setText ...

 W/dalvikvm(27797): threadid=1: thread exiting with uncaught exception (group=0x418b6700)
E/AndroidRuntime(27797): FATAL EXCEPTION: main
E/AndroidRuntime(27797): java.lang.RuntimeException: Unable to start activity ComponentInfo{…}: java.lang.NullPointerException
E/AndroidRuntime(27797): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
E/AndroidRuntime(27797):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
E/AndroidRuntime(27797):    at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:3740)
E/AndroidRuntime(27797):    at android.app.ActivityThread.access$700(ActivityThread.java:141)
E/AndroidRuntime(27797):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1262)
E/AndroidRuntime(27797):    at android.os.Handler.dispatchMessage(Handler.java:99)
E/AndroidRuntime(27797):    at android.os.Looper.loop(Looper.java:137)
E/AndroidRuntime(27797):    at android.app.ActivityThread.main(ActivityThread.java:5103)
E/AndroidRuntime(27797):    at java.lang.reflect.Method.invokeNative(Native Method)
E/AndroidRuntime(27797):    at java.lang.reflect.Method.invoke(Method.java:525)
E/AndroidRuntime(27797):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
E/AndroidRuntime(27797):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
E/AndroidRuntime(27797):    at dalvik.system.NativeStart.main(Native Method)
E/AndroidRuntime(27797): Caused by: java.lang.NullPointerException
E/AndroidRuntime(27797):    at app.package.onCreate(AppName.java:68)
E/AndroidRuntime(27797):    at android.app.Activity.performCreate(Activity.java:5133)
E/AndroidRuntime(27797):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
E/AndroidRuntime(27797):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
E/AndroidRuntime(27797):    ... 12 more

這是我的整個onCreate方法，因為許多評論員都要求查看整個方法。 希望能幫助到你！

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity);

          // check if app just started or is being restored from memory
          if ( savedInstanceState == null ) // the app just started running
          {
             winCount = 0; 
             loseCount = 0; 
          } 
          else 
          {
             winCount = savedInstanceState.getInt("MY_POINTS");
             loseCount = savedInstanceState.getInt("HOUSE_POINTS");

             resultsTextView.setText(savedInstanceState.getString("RESULTS"));
             pointsTextView.setText(savedInstanceState.getString("POINTS"));
             rollTextView.setText(savedInstanceState.getString("ROLL"));
          } 


        die1 = (ImageView) findViewById(R.id.imageView1);
        die2 = (ImageView) findViewById(R.id.imageView2);
        dealButton = (Button) findViewById(R.id.dealButton);
        resetButton = (Button) findViewById(R.id.resetButton);
        resultsTextView = (TextView) findViewById(R.id.resultsTextView);
        myPointsTextView = (TextView) findViewById(R.id.myPointstTextView);
        housePointsTextView = (TextView) findViewById(R.id.housePointsTextView);
        pointsTextView = (TextView) findViewById(R.id.pointsTextView1);
        rollTextView = (TextView) findViewById(R.id.rollTextView);

        dealButton.setOnClickListener(dealButtonListener);
        resetButton.setOnClickListener(resetButtonLinstener);

        //on shake event
        mSensorManager = (SensorManager) getSystemService(SENSOR_SERVICE);
        mAccelerometer = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
        mShakeDetector = new ShakeDetector(new OnShakeListener() {

            @Override
            public void onShake() {
               game(rollDice());
            }
        });


        resultsTextView.setTextColor(Color.BLACK);
        myPointsTextView.setText(String.format("%s", winCount));
        housePointsTextView.setText(String.format("%s", loseCount));

    }

Answer 1

您應該在調用setText方法之前初始化TextView 。 所以onCreate應該像這樣：

        setContentView(R.layout.activity);

        die1 = (ImageView) findViewById(R.id.imageView1);
        die2 = (ImageView) findViewById(R.id.imageView2);
        dealButton = (Button) findViewById(R.id.dealButton);
        resetButton = (Button) findViewById(R.id.resetButton);
        resultsTextView = (TextView) findViewById(R.id.resultsTextView);
        myPointsTextView = (TextView) findViewById(R.id.myPointstTextView);
        housePointsTextView = (TextView) findViewById(R.id.housePointsTextView);
        pointsTextView = (TextView) findViewById(R.id.pointsTextView1);
        rollTextView = (TextView) findViewById(R.id.rollTextView);

          // check if app just started or is being restored from memory
          if ( savedInstanceState == null ) // the app just started running
          {
             winCount = 0; 
             loseCount = 0; 
          } 
          else 
          {
             winCount = savedInstanceState.getInt("MY_POINTS");
             loseCount = savedInstanceState.getInt("HOUSE_POINTS");

             resultsTextView.setText(savedInstanceState.getString("RESULTS"));
             pointsTextView.setText(savedInstanceState.getString("POINTS"));
             rollTextView.setText(savedInstanceState.getString("ROLL"));
          } 
...