Android endless scroll list view
I want to implement OnScrollListener
to load more data when scrolling down, dynamically. The following code gives me a NullPointerException, but when I declare
BusinessListDataAdapter adapter = new BusinessListDataAdapter(this,
this.imgFetcher, this.layoutInflator, this.businesses);
inside setBusiness
, it shows no errors and works fine. The problem is that when I view the bottom of the page, it replaces the current data in the list view
new data, but I want infinite scrolling when new data is added instead of replacing so that I can view the first data by scrolling
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<BusinessListData> 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<BusinessListData>) 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<BusinessListData> 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);
}
}
}
Here is the logcat
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)
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There are three things you need to do.
1) Create a method that will add ten more items to the adapter list.
2) Add xml containing button in listview footer.
3) Then write a clickListener for that button in the activity or fragment class where you call the method of step 1 and then just reset the listview adapter.
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From Android - ListView to load more products upon reaching the end
You can add a footer in the ListView that will have a button named LoadMore. Here is a complete tutorial List with more loading Or you can implement onscrolllistener () and add this listener to your ListView
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
this.currentFirstVisibleItem = firstVisibleItem;
this.currentVisibleItemCount = visibleItemCount;
}
public void onScrollStateChanged(AbsListView view, int scrollState) {
this.currentScrollState = scrollState;
this.isScrollCompleted();
}
private void isScrollCompleted() {
if (this.currentVisibleItemCount > 0 && this.currentScrollState == SCROLL_STATE_IDLE) {
/*** In this way I detect if there been a scroll which has completed ***/
/*** do the work for load more date! ***/
if(!isLoading){
isLoading = true;
loadMoreData();
}
}
}
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Hi @carefree here is a solution that can give you exactly what you want to achieve https://github.com/rahulinaction/ImageGrid
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The problem will most likely be related to your task and adapter not scrolling the list. You can implement addItems method on your listAdapter like this:
public void addItems(BusniessListData... newItems){
for(BusniessListData newItem : newItems){
this.businesses.add(newItem);
}
notifyDataSetChanged();
}
In your task's onPostExecute, or whatever callback you use, check to see if the listAdapter has items and then calls addItems, passing in the newly loaded items. Otherwise, initiate and populate the selected dataset.
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