尝试在空对象引用上调用接口方法'java.lang.Object [] java.util.Collection.toArray（）'

Question

I have trouble loading data from remote server to my list view. It is showing the above mentioned error, and the app crashes as soon as I open the list. I have highlighted the functions where the error occurs in log cat. I also mentioned where is the fuction in my classes.

public class Library extends Fragment {
private MaterialSearchView searchView;
Librarycontact currentItem;
private SimpleAdapterLibrary adpt;
List<Librarycontact> result;
ListView lView ;
 ;

public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View v = inflater.inflate(R.layout.lib, container, false);

    setHasOptionsMenu(true);

    searchView = (MaterialSearchView)v.findViewById(R.id.search_view);
    searchView.setVoiceSearch(true); //or false
  //  searchView.setSuggestions(getResources().getStringArray(R.array.query_suggestions));
 //   searchView.setCursorDrawable(R.drawable.custom_cursor);

    adpt  = new SimpleAdapterLibrary(new ArrayList<Librarycontact>(), getActivity());
    lView = (ListView) v.findViewById(R.id.list);
    searchView.setOnQueryTextListener(new MaterialSearchView.OnQueryTextListener() {


        @Override
        public boolean onQueryTextSubmit(String query) {


            for (int i = 0; i < lView.getAdapter().getCount(); i++) {
                currentItem = result.get(i);

                if (query.contentEquals(currentItem.getitmCode())) {

                    Intent l = new Intent(getActivity(), SingleBook.class);

                    l.putExtra("id", currentItem.getid());
                    l.putExtra("itemname", currentItem.getitemname());
                    l.putExtra("itmCode", currentItem.getitmCode());

                    l.putExtra("itmRate", currentItem.getitmRate());

                    startActivity(l);
                    break;

                } else

                {

                    Toast.makeText(getActivity(), "No Match Found", Toast.LENGTH_SHORT).show();
                }
            }

            return false;
        }

        @Override
        public boolean onQueryTextChange(String newText) {

            return false;
        }
    });

    searchView.setOnSearchViewListener(new MaterialSearchView.SearchViewListener() {
        @Override
        public void onSearchViewShown() {

        }

        @Override
        public void onSearchViewClosed() {

        }
    });
    lView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        public void onItemClick(AdapterView<?> parent, View view,
                                int position, long id) {
            currentItem = result.get(position);
            Intent i = new Intent(getActivity() ,SingleBook.class);

            i.putExtra("id", currentItem.getid());
            i.putExtra("itemname", currentItem.getitemname());
            i.putExtra("itmCode", currentItem.getitmCode());

            i.putExtra("itmRate", currentItem.getitmRate());

            startActivity(i);

        }
    });

    searchView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {

            currentItem = result.get(position);
            Intent i = new Intent(getActivity(), SingleBook.class);

            i.putExtra("id", currentItem.getid());
            i.putExtra("itemname", currentItem.getitemname());
            i.putExtra("itmCode", currentItem.getitmCode());

            i.putExtra("itmRate", currentItem.getitmRate());

            startActivity(i);

        }

    });

    if (isAvailable()){   lView.setAdapter(adpt);
        // Exec async load task
        (new AsyncListViewLoader()).execute("http://minor.esy.es/libraryavailabilityofbooks.php");
    }
    else{
        showAlertDialog(getActivity(), "No Internet Connection",
                "Please Check Your Internet Connection And Try Again", false);
    }
    return v;}
public Boolean isAvailable() {
    try {
        Process p1 = java.lang.Runtime.getRuntime().exec("ping -c 1    www.google.com");
        int returnVal = p1.waitFor();
        boolean reachable = (returnVal==0);
        if(reachable){
            System.out.println("Internet access");
            return reachable;
        }
        else{
            System.out.println("No Internet access");
        }

    } catch (Exception e) {

        e.printStackTrace();
    }
    return false;
}
public void showAlertDialog(Context context, String title, String message, Boolean status) {
    AlertDialog alertDialog = new AlertDialog.Builder(context).create();
    alertDialog.setCancelable(false);
    // Setting Dialog Title
    alertDialog.setTitle(title);

    // Setting Dialog Message
    alertDialog.setMessage(message);

    // Setting alert dialog icon

    // Setting OK Button
    alertDialog.setButton("OK", new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface dialog, int which) {
        }
    });

    // Showing Alert Message
    alertDialog.show();

}
@Override
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
    inflater.inflate(R.menu.menu_main, menu);

    MenuItem item = menu.findItem(R.id.action_search);

    searchView.setMenuItem(item);

}

HERE **private class AsyncListViewLoader extends AsyncTask<String, Void, List<Librarycontact>> {**
    private final ProgressDialog dialog = new ProgressDialog(getActivity());

    @Override
    protected void onPostExecute(List<Librarycontact> result) {

        super.onPostExecute(result);
        dialog.dismiss();
        adpt.getItemList();
        **adpt.setItemList(result);** HERE
        adpt.notifyDataSetChanged();
    }

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        dialog.setMessage("Loading information...");
        dialog.show();
    }

    @Override
    protected List<Librarycontact> doInBackground(String... params) {
        result = new ArrayList<>();

        try {
            URL u = new URL(params[0]);

            HttpURLConnection conn = (HttpURLConnection) u.openConnection();
            conn.setRequestMethod("GET");

            conn.connect();
            InputStream is = conn.getInputStream();

            // Read the stream
            byte[] b = new byte[1024];
            ByteArrayOutputStream baos = new ByteArrayOutputStream();

            while ( is.read(b) != -1)
                baos.write(b);

            String JSONResp = new String(baos.toByteArray());

            JSONArray arr = new JSONArray(JSONResp);
            for (int i=0; i < arr.length(); i++) {
                result.add(convertContact(arr.getJSONObject(i)));
            }

            return result;
        }
        catch(Throwable t) {
            t.printStackTrace();
        }
        return null;
    }

    private Librarycontact convertContact(JSONObject obj) throws JSONException {
        String itemname = obj.getString("availability");
        String itmCode = obj.getString("title");
        String id = obj.getString("id");
        String itmRate = obj.getString("authorname");

        return new Librarycontact(itemname, itmCode, id,itmRate);
    }


}




@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
    if (requestCode == MaterialSearchView.REQUEST_VOICE && resultCode == getActivity().RESULT_OK) {
        ArrayList<String> matches = data.getStringArrayListExtra(RecognizerIntent.EXTRA_RESULTS);
        if (matches != null && matches.size() > 0) {
            String searchWrd = matches.get(0);
            if (!TextUtils.isEmpty(searchWrd)) {
                searchView.setQuery(searchWrd, false);
            }
        }

        return;
    }
    super.onActivityResult(requestCode, resultCode, data);
}

my data model

public class Librarycontact implements Serializable {



private String itemname;

private String id;

private String itmCode;
private String itmRate;

public Librarycontact(String name, String itmCode, String id,String itmRate) {
    super();
    this.itemname = name;
    this.itmCode = itmCode;
    this.id = id;
    this.itmRate = itmRate;
}

public String getitemname() {
    return itemname;
}

public void setName(String itemname) {
    this.itemname = itemname;
}

public String getitmCode() {
    return itmCode;
}

public void setitmCode(String itmCode) {
    this.itmCode = itmCode;
}

public String getid() {
    return id;
}

public void setid(String id) {
    this.id = id;
}

public String getitmRate() {
    return itmRate;
}

public void setitmRate(String itmRate) {
    this.itmRate = itmRate;
}
}

and my adapter

public class SimpleAdapterLibrary extends ArrayAdapter<Librarycontact> {

private List<Librarycontact> itemList;
private Context context;
private ArrayList<Librarycontact> contactListOrigin = new ArrayList<Librarycontact>();


   public SimpleAdapterLibrary(List<Librarycontact> itemListt, Context ctx) {
    super(ctx, android.R.layout.simple_list_item_1, itemListt);
    this.itemList = itemListt;
    this.context = ctx;

    this.contactListOrigin.addAll(itemListt);

}


public int getCount() {
    if (itemList != null)
        return itemList.size();
    return 0;
}
public Librarycontact getItem(int position) {
    if (itemList != null)
        return itemList.get(position);

    return null;
}

public long getItemId(int position) {
    if (itemList != null)
        return itemList.get(position).hashCode();
    return 0;
}

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

    View v = convertView;
    if (v == null) {
        LayoutInflater inflater = (LayoutInflater) context
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        v = inflater.inflate(R.layout.liblistitem, null);
    }

    Librarycontact c = itemList.get(position);
    //TextView text = (TextView) v.findViewById(R.id.name);
    //text.setText(c.getitemname());

    TextView text1 = (TextView) v.findViewById(R.id.name);
    text1.setText(c.getitmCode());
    String g= c.getitmCode();
    Character o =  g.charAt(0);

    String k = o.toString();
    TextDrawable drawable = TextDrawable.builder()
            .beginConfig()
            .textColor(Color.BLACK)
            .useFont(Typeface.DEFAULT)
            .fontSize(30)
            .bold()
            .toUpperCase()
            .endConfig()
            .buildRoundRect(k, Color.RED, 10); // radius in px


    ImageView img = (ImageView) v.findViewById(R.id.imageView2);
    img.setImageDrawable(drawable);

    /*       TextView text2 = (TextView) v.findViewById(R.id.email);
    text2.setText(c.getid());

    TextView text3 = (TextView) v.findViewById(R.id.phone);
    text3.setText(c.getitmRate());
    */
    return v;

}

public List<Librarycontact> getItemList() {

    if (itemList == null)
        return Collections.emptyList();
    else


    return itemList;
}

public void setItemList(List<Librarycontact> itemListt) {
    this.itemList = itemListt;
    **contactListOrigin.addAll(itemListt);** HERE 
}}

my logcat

11-09 02:01:25.892 4998-4998/essentials.gtbit.com.gtbitessentials E/AndroidRuntime: FATAL EXCEPTION: main
11-09 02:01:25.892 4998-4998/essentials.gtbit.com.gtbitessentials E/AndroidRuntime: Process: essentials.gtbit.com.gtbitessentials, PID: 4998
11-09 02:01:25.892 4998-4998/essentials.gtbit.com.gtbitessentials E/AndroidRuntime: java.lang.NullPointerException: Attempt to invoke interface method 'java.lang.Object[] java.util.Collection.toArray()' on a null object reference
11-09 02:01:25.892 4998-4998/essentials.gtbit.com.gtbitessentials E/AndroidRuntime:     at java.util.ArrayList.addAll(ArrayList.java:188)
11-09 02:01:25.892 4998-4998/essentials.gtbit.com.gtbitessentials E/AndroidRuntime:     at essentials.gtbit.com.gtbitessentials.SimpleAdapterLibrary.setItemList(SimpleAdapterLibrary.java:110)
11-09 02:01:25.892 4998-4998/essentials.gtbit.com.gtbitessentials E/AndroidRuntime:     at essentials.gtbit.com.gtbitessentials.Library$AsyncListViewLoader.onPostExecute(Library.java:215)
11-09 02:01:25.892 4998-4998/essentials.gtbit.com.gtbitessentials E/AndroidRuntime:     at essentials.gtbit.com.gtbitessentials.Library$AsyncListViewLoader.onPostExecute(Library.java:206)
11-09 02:01:25.892 4998-4998/essentials.gtbit.com.gtbitessentials E/AndroidRuntime:     at android.os.AsyncTask.finish(AsyncTask.java:632)
11-09 02:01:25.892 4998-4998/essentials.gtbit.com.gtbitessentials E/AndroidRuntime:     at android.os.AsyncTask.access$600(AsyncTask.java:177)
11-09 02:01:25.892 4998-4998/essentials.gtbit.com.gtbitessentials E/AndroidRuntime:     at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645)
11-09 02:01:25.892 4998-4998/essentials.gtbit.com.gtbitessentials E/AndroidRuntime:     at android.os.Handler.dispatchMessage(Handler.java:111)
11-09 02:01:25.892 4998-4998/essentials.gtbit.com.gtbitessentials E/AndroidRuntime:     at android.os.Looper.loop(Looper.java:194)
11-09 02:01:25.892 4998-4998/essentials.gtbit.com.gtbitessentials E/AndroidRuntime:     at android.app.ActivityThread.main(ActivityThread.java:5576)
11-09 02:01:25.892 4998-4998/essentials.gtbit.com.gtbitessentials E/AndroidRuntime:     at java.lang.reflect.Method.invoke(Native Method)
11-09 02:01:25.892 4998-4998/essentials.gtbit.com.gtbitessentials E/AndroidRuntime:     at java.lang.reflect.Method.invoke(Method.java:372)
11-09 02:01:25.892 4998-4998/essentials.gtbit.com.gtbitessentials E/AndroidRuntime:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:956)
11-09 02:01:25.892 4998-4998/essentials.gtbit.com.gtbitessentials E/AndroidRuntime:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:751)

Answer 1

You have to do this in class SimpleAdapterLibrary :

 public void setItemList(List<Librarycontact> itemListt) {
        if(itemListt==null) {
                return;
        }
        this.itemList = itemListt;
        contactListOrigin.addAll(itemListt);
    }

or in class AsyncListViewLoader :

 @Override
    protected void onPostExecute(List<Librarycontact> result) {
        super.onPostExecute(result);
        dialog.dismiss();
        if(result!=null){
                adpt.setItemList(result);
                adpt.notifyDataSetChanged();
        }        
    }