NullPointerException, Android, bundle

Question

Puzzled about some code that does not work.

I am attempted to pass selected items from a list to a new activity. So, I have the code to capture selected items:

 @Override
    //when listItem is clicked
    protected void onListItemClick(ListView l, View v, int position, long id) {
        super.onListItemClick(l, v, position, id);

        //in checked, in listview get Item positions for checked items
        SparseBooleanArray checked = l.getCheckedItemPositions();

        //assign selected items to new String ArrayList
        ArrayList<String> selectedItems = new ArrayList<String>();


        //determine size of items checked (number)
        for (int i = 0; i < checked.size(); i++) {
            // Item position in adapter
            position = checked.keyAt(i);
            // Add location if it is checked i.e.) == TRUE!
            if (checked.valueAt(i))
                //add selected items to madapter
                selectedItems.add(madapter.getItem(position));
        }

        //create string output array, store new string array with selected items
        String[] outputStrArr = new String[selectedItems.size()];

        for (int i = 0; i < selectedItems.size(); i++) {
            outputStrArr[i] = selectedItems.get(i);
        }

        Intent intent = new Intent(getApplicationContext(),
                MidwifeResultList.class);

        // Create a bundle object
        Bundle b = new Bundle();


        b.putStringArray("selectedItems", outputStrArr);

        // Add the bundle to the intent.
        intent.putExtras(b);

        // start the ResultActivity
        startActivity(intent);

And I have an activity that retrieves the bundle:

 protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_midwife_result_list);

        Bundle b = getIntent().getExtras();

        String[] resultArr = b.getStringArray("selectedItems");

        ListView lv = (ListView) findViewById(R.id.list);

        ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, resultArr);

        lv.setAdapter(adapter);


    }

However, when I run the app, it stops at the point of attempting to get to the new activty (nullpointerexception, pointing to the lv.setAdapter(adapter) line.

From what I researched, that error refers to a variable not properly instantiated..is there something wrong with how I am doing that for adapter? My first guess was that the selected item was not being properly captured, so when the new activity was attempting to retrieve information, it was coming up null.

Any help would be appreciated..thank you.

List:

<?xml version="1.0" encoding="utf-8"?>
<ListView xmlns:android="http://schemas.android.com/apk/res/android"
          android:id="@android:id/list"
          android:layout_width="fill_parent"
          android:layout_height="fill_parent" />

Log:

04-20 15:09:47.619  32662-32662/android.bignerdranch.com.mobilemidwife E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: android.bignerdranch.com.mobilemidwife, PID: 32662
    java.lang.RuntimeException: Unable to start activity ComponentInfo{android.bignerdranch.com.mobilemidwife/android.bignerdranch.com.mobilemidwife.MidwifeResultList}: java.lang.NullPointerException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2305)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2363)
            at android.app.ActivityThread.access$900(ActivityThread.java:161)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1265)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:157)
            at android.app.ActivityThread.main(ActivityThread.java:5356)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at android.bignerdranch.com.mobilemidwife.MidwifeResultList.onCreate(MidwifeResultList.java:39)
            at android.app.Activity.performCreate(Activity.java:5426)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2269)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2363)
            at android.app.ActivityThread.access$900(ActivityThread.java:161)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1265)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:157)
            at android.app.ActivityThread.main(ActivityThread.java:5356)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)

Answer 1

If the error that is throwing is a NullPointerException at lv.setAdapter(adapter) that only means one thing: lv = null. So the reason can be that you are referencing an id that is not in the view inflated in setContentView. Things to check:

• In activity_midwife_result_list do you have a ListView with the id "list"?
• R.id.list is refering an id from Android platorm or from your R class resource?

Answer 2

Instead of the code :-

<ListView xmlns:android="http://schemas.android.com/apk/res/android"
          android:id="@android:id/list"
          android:layout_width="fill_parent"
          android:layout_height="fill_parent" />

put this code:-

<ListView xmlns:android="http://schemas.android.com/apk/res/android"
          android:id="@+id/list"                 //change on this line
          android:layout_width="fill_parent"
          android:layout_height="fill_parent" />