Бесконечный список прокрутки Android ⇐ Android

[Anonymous]

Я хочу реализовать OnScrollListener для динамической загрузки большего количества данных при прокрутке вниз. Следующий код выдает мне NullPointerException, но когда я объявляю


BusinessListDataAdapter adapter = new BusinessListDataAdapter(this,
this.imgFetcher, this.layoutInflator, this.businesses);



внутри setBusiness, он не показывает никаких ошибок и работает нормально. Проблема в том, что когда я прокручиваю страницу вниз, текущие данные в виде списка заменяются новыми данными, но мне нужна была бесконечная прокрутка при добавлении новых данных вместо замены, чтобы я мог просмотреть первые данные, прокручивающиеся вверх

import java.util.ArrayList;

import com.sp.sodhpuch.adapters.BusinessListDataAdapter;
import com.sp.sodhpuch.data.BusinessListData;
import com.sp.sodhpuch.tasks.BusinessListApiTask;
import com.sp.sodhpuch.tasks.BusinessListIconTask;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.widget.AbsListView;
import android.widget.AbsListView.OnScrollListener;
import android.widget.BaseAdapter;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;

public class ListResultActivity extends Activity {

private ArrayList businesses;
private ListView businessList;
private LayoutInflater layoutInflator;
private BusinessListIconTask imgFetcher;
BusinessListDataAdapter adapter = new BusinessListDataAdapter(this,
this.imgFetcher, this.layoutInflator, this.businesses);

@SuppressWarnings("unchecked")
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.businesslist);
getData();
// @SuppressWarnings("deprecation")
// final Object[] data = (Object[]) getLastNonConfigurationInstance();
// if (data != null) {
// setContentView(R.layout.businesslist);
// this.businessList = (ListView) findViewById(R.id.lvBusinesslist);
// this.imgFetcher = new BusinessListIconTask(this);
// this.layoutInflator = LayoutInflater.from(this);
//
// this.businesses = (ArrayList) data[0];
// this.imgFetcher = (BusinessListIconTask) data[1];
// businessList.setAdapter(adapter);
// }
}

@Override
public Object onRetainNonConfigurationInstance() {
Object[] myStuff = new Object[2];
myStuff[0] = this.businesses;
myStuff[1] = this.imgFetcher;
return myStuff;
}

/**
* Bundle to hold refs to row items views.
*
*/
public static class MyViewHolder {
public TextView businessName, businessAddress, phoneNo;
public Button btnProfile;
public ImageView icon;
public BusinessListData business;
}

public void setBusinesses(ArrayList businesses) {
this.businessList = (ListView) findViewById(R.id.lvBusinesslist);

this.imgFetcher = new BusinessListIconTask(this);
this.layoutInflator = LayoutInflater.from(this);
this.businesses = businesses;
this.businessList.setAdapter(adapter);
businessList.setOnScrollListener(new OnScrollListener() {
public void onScrollStateChanged(AbsListView view, int scrollState) {

}

@Override
public void onScroll(AbsListView view, int firstVisibleItem,
int visibleItemCount, int totalItemCount) {
if (businessList.getLastVisiblePosition() == totalItemCount - 1) {
getData();
// adapter.notifyDataSetChanged();
}

}
});

}

private void getData() {
// TODO Auto-generated method stub
Intent myIntent = getIntent();

// gets the arguments from previously created intent
String metroTxt = myIntent.getStringExtra("key");
String metroLoc = myIntent.getStringExtra("loc");
String metroId = myIntent.getStringExtra("qt");

BusinessListApiTask spTask = new BusinessListApiTask(
ListResultActivity.this);

try {
spTask.execute(metroTxt, metroLoc, metroId);

} catch (Exception e) {
spTask.cancel(true);
}
}

}


Вот логарифм

10-17 04:50:51.897: W/dalvikvm(6942): threadid=1: thread exiting with uncaught exception (group=0xb1d41b20)
10-17 04:50:51.897: E/AndroidRuntime(6942): FATAL EXCEPTION: main
10-17 04:50:51.897: E/AndroidRuntime(6942): Process: com.sp.sodhpuch, PID: 6942
10-17 04:50:51.897: E/AndroidRuntime(6942): java.lang.NullPointerException
10-17 04:50:51.897: E/AndroidRuntime(6942): at com.sp.sodhpuch.adapters.BusinessListDataAdapter.getCount(BusinessListDataAdapter.java:53)
10-17 04:50:51.897: E/AndroidRuntime(6942): at android.widget.ListView.setAdapter(ListView.java:480)
10-17 04:50:51.897: E/AndroidRuntime(6942): at com.sp.sodhpuch.ListResultActivity.setBusinesses(ListResultActivity.java:78)
10-17 04:50:51.897: E/AndroidRuntime(6942): at com.sp.sodhpuch.tasks.BusinessListApiTask.onPostExecute(BusinessListApiTask.java:119)
10-17 04:50:51.897: E/AndroidRuntime(6942): at com.sp.sodhpuch.tasks.BusinessListApiTask.onPostExecute(BusinessListApiTask.java:1)
10-17 04:50:51.897: E/AndroidRuntime(6942): at android.os.AsyncTask.finish(AsyncTask.java:632)
10-17 04:50:51.897: E/AndroidRuntime(6942): at android.os.AsyncTask.access$600(AsyncTask.java:177)
10-17 04:50:51.897: E/AndroidRuntime(6942): at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645)
10-17 04:50:51.897: E/AndroidRuntime(6942): at android.os.Handler.dispatchMessage(Handler.java:102)
10-17 04:50:51.897: E/AndroidRuntime(6942): at android.os.Looper.loop(Looper.java:136)
10-17 04:50:51.897: E/AndroidRuntime(6942): at android.app.ActivityThread.main(ActivityThread.java:5017)
10-17 04:50:51.897: E/AndroidRuntime(6942): at java.lang.reflect.Method.invokeNative(Native Method)
10-17 04:50:51.897: E/AndroidRuntime(6942): at java.lang.reflect.Method.invoke(Method.java:515)
10-17 04:50:51.897: E/AndroidRuntime(6942): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
10-17 04:50:51.897: E/AndroidRuntime(6942): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
10-17 04:50:51.897: E/AndroidRuntime(6942): at dalvik.system.NativeStart.main(Native Method)


Подробнее здесь: https://stackoverflow.com/questions/264 ... -list-view