title: android: bundle string-array from one activity to another
body: <p>I am making a quiz where the question and answer lists are needed to pass from activity 1 to activity 2. Relevant Codings extracted as follows:</p>
  
  <h2>Activity 1: Num_index.java</h2>
  
  <pre><code>   String[] NUM_ALLL_QuestionNames; 
     String[] NUM_ALLL_AnswerNames;   
  
     @Override
     public void onCreate(Bundle savedInstanceState) 
     {
        super.onCreate(savedInstanceState); 
        setContentView(R.layout.main_num_index); 
  
        Button ButtonStart= (Button) findViewById(R.id.buttonStart);
        ButtonStart.setOnClickListener(startButtonListener);
  
        Button ButtonBackkk= (Button) findViewById(R.id.buttonBackkk);
  
        CheckTextView = (TextView) findViewById(R.id.checktextView); 
  
        NUM_SIM_QuestionNames = getResources().getStringArray(R.array.Num_Q_Simple_List);
        NUM_MED_QuestionNames = getResources().getStringArray(R.array.Num_Q_Medium_List);
        NUM_DIF_QuestionNames = getResources().getStringArray(R.array.Num_Q_Diff_List);
        NUM_EXP_QuestionNames = getResources().getStringArray(R.array.Num_Q_Expert_List);
  
        NUM_SIM_AnswerNames = getResources().getStringArray(R.array.Num_A_Simple_List);
        NUM_MED_AnswerNames = getResources().getStringArray(R.array.Num_A_Medium_List);
        NUM_DIF_AnswerNames = getResources().getStringArray(R.array.Num_A_Diff_List);
        NUM_EXP_AnswerNames = getResources().getStringArray(R.array.Num_A_Expert_List);
  
        NUM_ALL_QuestionNames = new ArrayList&lt;String&gt;();
        NUM_ALL_AnswerNames = new ArrayList&lt;String&gt;();                              
     };
  
     private OnClickListener startButtonListener = new OnClickListener() 
     {
        @Override
        public void onClick(View v) 
        {
            CheckBox CheckSim = (CheckBox) findViewById(R.id.checkBox2);
            // other similar checkBox omitted here for simplicity // 
  
            NUM_ALL_QuestionNames.clear();
            NUM_ALL_AnswerNames.clear();  
  
            if (CheckSim.isChecked()) 
            {
                QuestionImport= 0;                  
                QuestionImport = NUM_SIM_QuestionNames.length;
                int i =0;
                while (i&lt;QuestionImport)
                {
                    String Q_toimport = NUM_SIM_QuestionNames[i];
                    String A_toimport = NUM_SIM_AnswerNames[i];   
  
                    NUM_ALL_QuestionNames.add(Q_toimport);
                    NUM_ALL_AnswerNames.add(A_toimport);                    
                    ++i;                    
                }           
            };    
  
           // other similar checkBox omitted here for simplicity // 
  
            if ((!CheckSim.isChecked()) &amp;&amp; (!CheckMed.isChecked()) &amp;&amp; (!CheckDif.isChecked()) &amp;&amp; (!CheckExp.isChecked()))  
            {
                int k = 0;
                if (NUM_ALL_QuestionNames.size() &gt;0) {k= NUM_ALL_QuestionNames.size();}
                CheckTextView.setText(String.valueOf(k));
  
                  AlertDialog.Builder builder = new AlertDialog.Builder(Num_index.this);
                  builder.setTitle("Error");
                  builder.setMessage("Please select at least one choice!!");
                  builder.setCancelable(false);
                  builder.setPositiveButton("OK", null);                 
                  AlertDialog ErrorDialog = builder.create();
                  ErrorDialog.show();                   
            }
  
            if ((CheckSim.isChecked()) || (CheckMed.isChecked()) || (CheckDif.isChecked()) || (CheckExp.isChecked()))  
            {
                NUM_ALLL_QuestionNames = new String[NUM_ALL_QuestionNames.size()]; //convert ArrayList&lt;String&gt; to String[]
                NUM_ALLL_AnswerNames = new String[NUM_ALL_AnswerNames.size()]; //convert ArrayList&lt;String&gt; to String[]
  
                Intent senddata = new Intent (Num_index.this, Num.class); //transmit the list to num.java
                Bundle bundle = new Bundle();
                bundle.putStringArray("dataQ",NUM_ALLL_QuestionNames);
                bundle.putStringArray("dataA",NUM_ALLL_AnswerNames);
                senddata.putExtras(bundle);
                startActivity(senddata);                            
  
                int k = 0;
                if (NUM_ALLL_QuestionNames.length &gt;0) {k= NUM_ALLL_QuestionNames.length;}
                CheckTextView.setText(String.valueOf(k));                                   
            }           
  
             Intent intent = new Intent (Num_index.this, Num.class);
             startActivity(intent);
             Num_index.this.finish();               
  
        } // end method onClick
     }; // end OnClickListener    
  </code></pre>
  
  <h2>Activity 2: Num.java</h2>
  
  <pre><code>   private String[] NUM_ALL_QuestionNames;
     private String[] NUM_ALL_AnswerNames;
  
     @Override
     public void onCreate(Bundle savedInstanceState) 
     {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main_num); 
  
        //get bundle from Num_index.java
        Bundle bundle = this.getIntent().getExtras();
        if (bundle!= null)
        {
            NUM_ALL_QuestionNames = bundle.getStringArray("dataQ");
            NUM_ALL_AnswerNames = bundle.getStringArray("dataA");          
        }
        else
        {
            NUM_ALL_QuestionNames = getResources().getStringArray(R.array.Num_Q_Simple_List);
            NUM_ALL_AnswerNames = getResources().getStringArray(R.array.Num_A_Simple_List);             
        }
  </code></pre>
  
  <h2>Logcat:</h2>
  
  <pre><code>11-18 20:26:20.905: E/AndroidRuntime(5463): FATAL EXCEPTION: main
  11-18 20:26:20.905: E/AndroidRuntime(5463): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.pearappx.iq_3/com.pearappx.iq_3.Num}: java.lang.NullPointerException
  11-18 20:26:20.905: E/AndroidRuntime(5463):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1967)
  11-18 20:26:20.905: E/AndroidRuntime(5463):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1992)
  11-18 20:26:20.905: E/AndroidRuntime(5463):     at android.app.ActivityThread.access$600(ActivityThread.java:127)
  11-18 20:26:20.905: E/AndroidRuntime(5463):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1158)
  11-18 20:26:20.905: E/AndroidRuntime(5463):     at android.os.Handler.dispatchMessage(Handler.java:99)
  11-18 20:26:20.905: E/AndroidRuntime(5463):     at android.os.Looper.loop(Looper.java:137)
  11-18 20:26:20.905: E/AndroidRuntime(5463):     at android.app.ActivityThread.main(ActivityThread.java:4511)
  11-18 20:26:20.905: E/AndroidRuntime(5463):     at java.lang.reflect.Method.invokeNative(Native Method)
  11-18 20:26:20.905: E/AndroidRuntime(5463):     at java.lang.reflect.Method.invoke(Method.java:511)
  11-18 20:26:20.905: E/AndroidRuntime(5463):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:980)
  11-18 20:26:20.905: E/AndroidRuntime(5463):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:747)
  11-18 20:26:20.905: E/AndroidRuntime(5463):     at dalvik.system.NativeStart.main(Native Method)
  11-18 20:26:20.905: E/AndroidRuntime(5463): Caused by: java.lang.NullPointerException
  11-18 20:26:20.905: E/AndroidRuntime(5463):     at com.pearappx.iq_3.Num.onCreate(Num.java:73)
  11-18 20:26:20.905: E/AndroidRuntime(5463):     at android.app.Activity.performCreate(Activity.java:4470)
  11-18 20:26:20.905: E/AndroidRuntime(5463):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1052)
  11-18 20:26:20.905: E/AndroidRuntime(5463):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1931)
  </code></pre>
  
  <p>Line 73 is </p>
  
  <pre><code>NUM_ALL_QuestionNames = bundle.getStringArray("dataQ"); 
  </code></pre>
  
  <p>which means the StringArray is not properly stored in Activity1 or cannot properly fetched in Activity2. It shows NullPointerException. </p>
  
  <h2>Question:</h2>
  
  <p>I have searched through this website like <a href="https://stackoverflow.com/questions/7652829/string-back-from-bundle">String back from Bundle</a> , and <a href="https://stackoverflow.com/questions/6277662/how-to-pass-the-selectedlistitems-object-to-another-activity">How to pass the selectedListItem&#39;s object to another activity?</a> and follow the method described but still fails. But why it is NullPointerException? How can this be tackled? </p>
  
  <p>Many thanks!!</p>
  
  <p>PS: In Activity 1 I have </p>
  
  <pre><code>              if (NUM_ALLL_QuestionNames.length &gt;0) {k= NUM_ALLL_QuestionNames.length;}
                CheckTextView.setText(String.valueOf(k)); 
  </code></pre>
  
  <p>and k gives out a correct number of items. This means NUM_ALLL_QuestionNames is not blank.</p>