设置自定义适配器时发生NullPointerException

Question

I'm trying to use a custom adapter with ListView on my main activity and it crashes. I've looked everywhere for an answer please help!

My main activity/ ListActivity:

public class ListRestaurantsMain extends ListActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_list_restaurants_main);

    //access myApp
    MyApplication myApp = MyApplication.getInstance();
    ArrayList <RestaurantObj> arr = new ArrayList <RestaurantObj>();

    arr = myApp.getArray();

    ListView lv = (ListView) findViewById(android.R.id.list);
    RatingAdapter adapter = new RatingAdapter(getApplicationContext(), arr);
    lv.setAdapter(adapter);


}
  @Override
  protected void onListItemClick(ListView lv, View v, int position, long id) {
      super.onListItemClick(lv, v, position, id); 

      Log.v("ClickListener", "Item at pos: " + position + " clicked.");
  }

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.list_restaurants_main, menu);
    return true;
}



}

My custom Adapter:

class RatingAdapter extends ArrayAdapter<RestaurantObj> {

public RatingAdapter(Context context, ArrayList<RestaurantObj> objects) {
    super(context, R.layout.list_row, R.id.title, objects);
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    View row = convertView;

    //get info from Restaurant Object
    RestaurantObj restObj = getItem(position);

    // create new inflater
        row = LayoutInflater.from(getContext()).inflate(R.layout.list_row, null);


    //display name of restaurant
    TextView restName = (TextView)row.findViewById(R.id.title);
    restName.setText(restObj.getName());

    //display rating
    RatingBar rb = (RatingBar) row.findViewById(R.id.ratingbar);
    rb.setRating(3); //grab rating from object

    return row;
}
}

Logcat

03-16 03:04:16.679: E/AndroidRuntime(1865): FATAL EXCEPTION: main
03-16 03:04:16.679: E/AndroidRuntime(1865): Process: com.example.restaurantrater, PID: 1865
03-16 03:04:16.679: E/AndroidRuntime(1865): java.lang.RuntimeException: Unable to start activity        ComponentInfo{com.example.restaurantrater/com.example.restaurantrater.ListRestaurantsMain}: java.lang.NullPointerException
03-16 03:04:16.679: E/AndroidRuntime(1865):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
03-16 03:04:16.679: E/AndroidRuntime(1865):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
03-16 03:04:16.679: E/AndroidRuntime(1865):     at android.app.ActivityThread.access$800(ActivityThread.java:135)
03-16 03:04:16.679: E/AndroidRuntime(1865):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
03-16 03:04:16.679: E/AndroidRuntime(1865):     at android.os.Handler.dispatchMessage(Handler.java:102)
03-16 03:04:16.679: E/AndroidRuntime(1865):     at android.os.Looper.loop(Looper.java:136)
03-16 03:04:16.679: E/AndroidRuntime(1865):     at android.app.ActivityThread.main(ActivityThread.java:5017)
03-16 03:04:16.679: E/AndroidRuntime(1865):     at java.lang.reflect.Method.invokeNative(Native Method)
03-16 03:04:16.679: E/AndroidRuntime(1865):     at java.lang.reflect.Method.invoke(Method.java:515)
03-16 03:04:16.679: E/AndroidRuntime(1865):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
03-16 03:04:16.679: E/AndroidRuntime(1865):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
03-16 03:04:16.679: E/AndroidRuntime(1865):     at dalvik.system.NativeStart.main(Native Method)
03-16 03:04:16.679: E/AndroidRuntime(1865): Caused by: java.lang.NullPointerException
03-16 03:04:16.679: E/AndroidRuntime(1865):     at android.widget.ArrayAdapter.getCount(ArrayAdapter.java:330)
03-16 03:04:16.679: E/AndroidRuntime(1865):     at android.widget.ListView.setAdapter(ListView.java:480)
03-16 03:04:16.679: E/AndroidRuntime(1865):     at com.example.restaurantrater.ListRestaurantsMain.onCreate(ListRestaurantsMain.java:32)
03-16 03:04:16.679: E/AndroidRuntime(1865):     at android.app.Activity.performCreate(Activity.java:5231)
03-16 03:04:16.679: E/AndroidRuntime(1865):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
03-16 03:04:16.679: E/AndroidRuntime(1865):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
03-16 03:04:16.679: E/AndroidRuntime(1865):     ... 11 more

I checked all the ids in the XMLs and they all exist and whatnot... I suspect my custom adapter is the problem but I don't understand what I'm doing wrong. Struggling student here with limited android experience, please help!

Answer 1

Firstly, you should reuse views if they exist instead of creating new ones when not needed, it saves ram and improves performance. Edit your getView() method like the following:

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    if (convertView == null) {
        convertView = LayoutInflater.from(getContext()).inflate(R.layout.list_row, null);
    }

    RestaurantObj restObj = getItem(position);

    TextView restName = (TextView)row.findViewById(R.id.title);
    restName.setText(restObj.getName());

    RatingBar rb = (RatingBar) row.findViewById(R.id.ratingbar);
    rb.setRating(3);

    return convertView;
}

Onto addressing your issue, as also Gabe said, the getArray() method from your application class is retuning null. Check that out.