从JSON创建ListAdapter

Question

I'm getting some problem in an Android APP: I want to read info from a Feed RSS and present them in some android view. I'm using the android-async-http1.4.3.jar libs to connect my APP to this site: http://ajax.googleapis.com/ajax/services/feed/load?v=1.0&num=10&q=http://f1grandprix.motorionline.com/feed/

With this connection I'm downloading the XML file and I'm transforming it into a JSON file with gson libs, but when i try the APP to my Android Phone I'm getting a Null Pointer Exception. The class to connect, to get the xml and to transform it into JSON code is the following:

    private void loadTitle() {
    String URL = "http://ajax.googleapis.com/ajax/services/feed/load?v=1.0&num=10&q=http://f1grandprix.motorionline.com/feed/";

    AsyncHttpClient client = new AsyncHttpClient();

    client.get(URL, new AsyncHttpResponseHandler() {
        @Override
        public void onSuccess(String text) {
            super.onSuccess(text);

            Gson decoder = new Gson();

            JsonResponse jr = decoder.fromJson(text, JsonResponse.class);

            Entry[] entries = jr.responseData.feed.entries;
            for (int i = 0; i < entries.length; i++) {
                Log.d("NET", "Il titolo della " + i + " entry è: " + entries[i].title);
            }


            final ListView lv_title = (ListView) findViewById(R.id.lv_title);
            //ListAdapter la_title = new TitleAdapter(MainActivity.this, entries);
            //Log.d("LIST_ADAPTER", "Caricato correttamente il list adaptor: "+ la_title);
            //lv_title.setAdapter(la_title);
            lv_title.setAdapter(new TitleAdapter(MainActivity.this, entries));
            pleaseWait.hide();
        }

        @Override
        public void onFailure(Throwable arg0, String arg1) {
            super.onFailure(arg0, arg1);
            Log.d("FAIL", "Failure");
            pleaseWait.hide();
        }
    });
}

The TitleAdapter.java is the following:

public class TitleAdapter extends ArrayAdapter<Entry> {

public TitleAdapter(Context context, Entry[] title) {
    super(context, R.layout.list_item, R.id.lv_title, title);
}

}

And finally I'm getting this error:

02-23 12:46:05.525: E/AndroidRuntime(4577): FATAL EXCEPTION: main
02-23 12:46:05.525: E/AndroidRuntime(4577): java.lang.NullPointerException
02-23 12:46:05.525: E/AndroidRuntime(4577):     at android.widget.ArrayAdapter.createViewFromResource(ArrayAdapter.java:355)
02-23 12:46:05.525: E/AndroidRuntime(4577):     at android.widget.ArrayAdapter.getView(ArrayAdapter.java:323)
02-23 12:46:05.525: E/AndroidRuntime(4577):     at android.widget.AbsListView.obtainView(AbsListView.java:1495)
02-23 12:46:05.525: E/AndroidRuntime(4577):     at android.widget.ListView.measureHeightOfChildren(ListView.java:1216)
02-23 12:46:05.525: E/AndroidRuntime(4577):     at android.widget.ListView.onMeasure(ListView.java:1127)
02-23 12:46:05.525: E/AndroidRuntime(4577):     at android.view.View.measure(View.java:8335)
02-23 12:46:05.525: E/AndroidRuntime(4577):     at android.widget.RelativeLayout.measureChild(RelativeLayout.java:566)
02-23 12:46:05.525: E/AndroidRuntime(4577):     at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:381)
02-23 12:46:05.525: E/AndroidRuntime(4577):     at android.view.View.measure(View.java:8335)
02-23 12:46:05.525: E/AndroidRuntime(4577):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138)
02-23 12:46:05.525: E/AndroidRuntime(4577):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:250)
02-23 12:46:05.525: E/AndroidRuntime(4577):     at android.view.View.measure(View.java:8335)
02-23 12:46:05.525: E/AndroidRuntime(4577):     at android.widget.LinearLayout.measureVertical(LinearLayout.java:531)
02-23 12:46:05.525: E/AndroidRuntime(4577):     at android.widget.LinearLayout.onMeasure(LinearLayout.java:309)
02-23 12:46:05.525: E/AndroidRuntime(4577):     at android.view.View.measure(View.java:8335)
02-23 12:46:05.525: E/AndroidRuntime(4577):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138)
02-23 12:46:05.525: E/AndroidRuntime(4577):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:250)
02-23 12:46:05.525: E/AndroidRuntime(4577):     at android.view.View.measure(View.java:8335)
02-23 12:46:05.525: E/AndroidRuntime(4577):     at android.view.ViewRoot.performTraversals(ViewRoot.java:843)
02-23 12:46:05.525: E/AndroidRuntime(4577):     at android.view.ViewRoot.handleMessage(ViewRoot.java:1892)
02-23 12:46:05.525: E/AndroidRuntime(4577):     at android.os.Handler.dispatchMessage(Handler.java:99)
02-23 12:46:05.525: E/AndroidRuntime(4577):     at android.os.Looper.loop(Looper.java:130)
02-23 12:46:05.525: E/AndroidRuntime(4577):     at android.app.ActivityThread.main(ActivityThread.java:3835)
02-23 12:46:05.525: E/AndroidRuntime(4577):     at java.lang.reflect.Method.invokeNative(Native Method)
02-23 12:46:05.525: E/AndroidRuntime(4577):     at java.lang.reflect.Method.invoke(Method.java:507)
02-23 12:46:05.525: E/AndroidRuntime(4577):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:864)
02-23 12:46:05.525: E/AndroidRuntime(4577):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:622)
02-23 12:46:05.525: E/AndroidRuntime(4577):     at dalvik.system.NativeStart.main(Native Method)

Can someone help me to fix this problem? Thank you!

Answer 1

Can someone help me to fix this problem?

In the entries array that you pass to your custom ArrayAdapter (for which you still call the super.getView() method(or you didn't overriden it), right?) it appears that you have null values. This is a problem if you use the default implementation of ArrayAdapter 's getView() method, as ArrayAdapter will call in that method, by default, the toString() method on its type object( Entry object in your case) to obtain a String to show in the row.

So make sure the array that you pass to your implementation of the ArrayAdapter doesn't contain null values.