Udacity Sunshine app - lesson 1 - NullPointerExcep

Question

I'm going through the Android dev training at udacity.com, following along with the implementation of the Sunshine app. I'm using Android Studio, latest version default installation.

I'm at the point where I'm supposed to have a ListView with the mock data, and I'm getting a NullPointerException:

07-23 13:12:51.371    1677-1677/com.mydomain.sunshine E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.mydomain.sunshine, PID: 1677
java.lang.NullPointerException
        at android.widget.ArrayAdapter.createViewFromResource(ArrayAdapter.java:392)
        at android.widget.ArrayAdapter.getView(ArrayAdapter.java:362)
        at android.widget.AbsListView.obtainView(AbsListView.java:2263)
        at android.widget.ListView.measureHeightOfChildren(ListView.java:1263)
        at android.widget.ListView.onMeasure(ListView.java:1175)
        at android.view.View.measure(View.java:16497)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
        at android.view.View.measure(View.java:16497)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
        at android.view.View.measure(View.java:16497)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
        at android.view.View.measure(View.java:16497)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
        at com.android.internal.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:327)
        at android.view.View.measure(View.java:16497)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
        at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2291)
        at android.view.View.measure(View.java:16497)
        at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1916)
        at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1113)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1295)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1000)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5670)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:761)
        at android.view.Choreographer.doCallbacks(Choreographer.java:574)
        at android.view.Choreographer.doFrame(Choreographer.java:544)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:747)
        at android.os.Handler.handleCallback(Handler.java:733)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:136)
        at android.app.ActivityThread.main(ActivityThread.java:5017)
        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:779)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
        at dalvik.system.NativeStart.main(Native Method)

I ran the debugger and identified it happens in here:

            listView.setAdapter(mForeCastAdapter);

When I comment that out it runs but obviously nothing is displayed, but at least it doesn't crash.

Here is my MainActivity.java's onCreateView() :

        @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_main, container, false);
        String[] forecastArray={
                "foo",
                "bar",
                "baz",
                "fiz",
        };
        List<String> weekForecast = new ArrayList<String> (Arrays.asList(forecastArray));
        mForeCastAdapter = new ArrayAdapter<String>(
                getActivity(),
                R.layout.list_item_forecast,
                R.id.listview_forecast,
                weekForecast);
        ListView listView = (ListView) rootView.findViewById(R.id.listview_forecast);
        listView.setAdapter(mForeCastAdapter);
        return rootView;
    }

Here is my fragment_main.xml:

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
tools:context=".MainActivity$PlaceholderFragment">

<ListView
    android:id="@+id/listview_forecast"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" /></FrameLayout>

and finally here is my list_item_forecast.xml:

<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_height="match_parent"
    android:layout_width="match_parent"
    android:minHeight="?android:attr/listPreferredItemHeight"
    android:gravity="center_vertical"
/>

My thanks!

Answer 1

Change:

mForeCastAdapter = new ArrayAdapter<String>(
                getActivity(),
                R.layout.list_item_forecast,
                R.id.listview_forecast,
                weekForecast);

to:

mForeCastAdapter = new ArrayAdapter<String>(
                getActivity(),
                R.layout.list_item_forecast,
                weekForecast);

The ID parameter in the constructor that you are using is supposed to be an ID of a TextView inside of your row layout. That is only needed if your row layout is more than a TextView, though. In your case:

• the row layout is only a TextView, so you do not need to provide the ID

• the ID you are providing is not for a TextView in your row layout, but rather for a ListView elsewhere

Answer 2

If the above solution does not work for you, and you are testing on a physical device, check that the portrait and landscape layouts both have the ListView declared. AS may create both files for you, and NPE will occur if the ListView is added only to one and then you switch orientations during testing.