獲取savedInstanceState值，NullPointerException異常

Question

@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.main2); 
    savedInstanceState.putString("foo", "bar"); 
} 

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

    String myString = savedInstanceState.getString("foo"); 

    Log.i("debug", "saved data: " + myString); 
} 

我試着在活動中保留一些價值，但我收到以下錯誤：06-23 23:09:44.038: E/AndroidRuntime(17584): java.lang.RuntimeException: Unable to start activity ComponentInfo{se.johanberntsson.activitytest/se.johanberntsson.activitytest.TestActivity}: java.lang.NullPointerException

我錯過了什麼嗎？在savedInstanceState捆綁節約值作爲感謝

Answer 1

覆蓋onSaveInstanceState：

public String strfoo=""; 
     @Override 
     public void onCreate(Bundle savedInstanceState) { 
      super.onCreate(savedInstanceState); 
      setContentView(R.layout.main2); 
      //comment this line you only fatch values from savedInstanceState 
      String myString = savedInstanceState.getString("foo"); 
      Log.i("debug", "saved data: " + myString); 
      // savedInstanceState.putString("foo", "bar"); 
      strfoo="bar"; set value here 
     } 

     @Override 
     public void onRestoreInstanceState(Bundle savedInstanceState) { 
      super.onRestoreInstanceState(savedInstanceState); 
      String myString = savedInstanceState.getString("foo"); 
      Log.i("debug", "saved data: " + myString); 
     } 

     @Override 

     public void onSaveInstanceState(Bundle savedInstanceState) { 
     savedInstanceState.putString("foo", strfoo); 
     super.onSaveInstanceState(savedInstanceState); 

     }