Custom Adapter starts before ArrayList is ready

Question

I'm making a list of links and for that I have made a custom adapter, but the list is not ready when the adapter starts so I get the following error:

java.lang.RuntimeException: Unable to start activity ComponentInfo{}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object android.content.Context.getSystemService(java.lang.String)' on a null object reference

this is because when the adapter is started the list is empty, and just moments after the list is filled but it's too late here is my code:

UPDATE: the code has been changed so now I du not get the error but it doesn't run getView in the adapter:

public class Controller extends Activity {

private String TAG = Controller.class.getSimpleName();
private String http;
CustomAdapter adapter;
public Controller con = null;
private ListView lv;
private static String url;
ArrayList<Selfservice> linkList = new ArrayList<Selfservice>();

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main_view);
    con = this;
    http = this.getString(R.string.http);
    url = this.getString(R.string.path1);

    new GetLinks().execute();

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

    //Resources res = getResources();
    //adapter = new CustomAdapter(con, linkList, res);
    //lv.setAdapter(adapter);
}

private class GetLinks extends AsyncTask<Void, Void, List<Selfservice>> {

    @Override
    protected void onPreExecute() {
        super.onPreExecute();

    }

    @Override
    protected List<Selfservice> doInBackground(Void... arg0) {
                Document doc;
                Elements links;
                List<Selfservice> returnList = null;
                try {
                    doc = Jsoup.connect(url).timeout(0).get();
                    links = doc.getElementsByClass("processlink");
                    returnList = ParseHTML(links);
                } catch (IOException e) {
                    e.printStackTrace();
                }

        return returnList;
    }

    @Override
    protected void onPostExecute(final List<Selfservice> result) {
        super.onPostExecute(result);
        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
                //setSupportActionBar(toolbar);
                //getSupportActionBar().setDisplayShowTitleEnabled(false);
                toolbar.setTitle("");
                toolbar.setSubtitle("");
                Resources res = getResources();
                Log.e(TAG, linkList.toString());
                linkList = (ArrayList<Selfservice>) result;
                adapter = new CustomAdapter(con, result, res);
                adapter.notifyDataSetChanged();
                lv.setAdapter(adapter);
            }
        });

    }

}

and my adapter:

public class CustomAdapter extends BaseAdapter implements OnClickListener {
private String TAG = CustomAdapter.class.getSimpleName();
Context context;
List<Selfservice> data;
private Activity activity;
public Resources res;
Selfservice self = null;
private static LayoutInflater inflater;
int layoutResourceId = 0;

public CustomAdapter(Activity act, List<Selfservice> dataList, Resources resources) {

    res = resources;
    activity = act;
    data = dataList;

}

private class Holder {
    TextView title;
    TextView link;
}

@Override
public int getCount() {

    return data.size();
}

@Override
public Object getItem(int pos) {
    return pos;
}

@Override
public long getItemId(int pos) {
    return pos;
}

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

    LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    View rowView = convertView;
    Holder holder;

    if(rowView == null){


        rowView = inflater.inflate(R.layout.list_item, null);
        holder = new Holder();
        holder.title = (TextView) rowView.findViewById(R.id.title);
        holder.link = (TextView) rowView.findViewById(R.id.link);

        rowView.setTag(holder);


    }else{
        holder = (Holder)rowView.getTag();
    }
    if(data.size()<=0){
        holder.title.setText("did not work");
    }else{
        self = null;
        self = (Selfservice) data.get(position);
        holder.title.setText(self.getTitle());
        holder.link.setText(self.getLink());
        Log.i(TAG, "adapter");
        rowView.setOnClickListener(new OnItemClickListener(position));
    }

    return rowView;
    }
@Override
public void onClick(View v){
    Log.v("CustomAdapter", "row clicked");
}

private class OnItemClickListener implements OnClickListener{
    private int mPos;

    OnItemClickListener(int position){
        mPos = position;
    }
    @Override
    public void onClick(View arg0){
        Controller con = (Controller)activity;
        con.onItemClick(mPos);
    }
    }
}

So How do I get the adapter to wait to the list is full?

Answer 1

You can create the adapter in the onPostExecute;

Change the Async Task to this:

    private class GetLinks extends AsyncTask<Void, Void, List<Selfservice>> {

        @Override 
        protected void onPreExecute() { 
            super.onPreExecute(); 

        } 

        @Override 
        protected Void doInBackground(Void... arg0) {
                    Document doc;
                    Elements links;
                    List<Selfservice> returnList

                    try { 
                        doc = Jsoup.connect(url).timeout(10000).get();
                        links = doc.getElementsByClass("processlink");
                        returnList = ParseHTML(links);
                    } catch (IOException e) {
                        e.printStackTrace();
                    } 

            return returnList; 
        } 

        @Override 
        protected void onPostExecute(List<Selfservice> result) {
            super.onPostExecute(result);
            runOnUiThread(new Runnable() {
                @Override 
                public void run() { 
                    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
                    //setSupportActionBar(toolbar); 
                    //getSupportActionBar().setDisplayShowTitleEnabled(false); 
                    toolbar.setTitle("");
                    toolbar.setSubtitle("");

                    linkList = result
                    adapter = new CustomAdapter(con, result, res);
                    lv.setAdapter(adapter);
                } 
            }); 

        } 

This way you will only create the adapter when your list is ready.

Edit: You are not creating the variable context inside your adapter. Change your constructor to this:

public CustomAdapter(Context context, Activity act, List<Selfservice> dataList, Resources resources) {

    res = resources;
    activity = act;
    data = dataList;
    this.context = context;

} 

And you will stop seeing the NullPointerExecption