我希望实现OnScrollListener以在动态滚动到底部时加载更多数据。下面的代码给了我NullPointerException，但是当我声明
BusinessListDataAdapter adapter = new BusinessListDataAdapter(this, this.imgFetcher, this.layoutInflator, this.businesses);
在setBusiness内，它没有显示任何错误并且工作正常。问题是，当我滚动到页面底部时，它用新数据替换list view中的当前数据，但我想要的是无限滚动，同时附加新数据而不是替换，以便我可以查看第一个数据向上滚动
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);
}
}
}
这是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)
答案 0 :(得分：0)
您需要做三件事。
1）创建方法，将另外10个项添加到适配器列表。
2）在listview页脚中添加包含按钮的xml。
3）然后在activity或fragment类中为该按钮编写clickListener，在该类中调用step 1方法，然后重置listview适配器。
答案 1 :(得分：0)
来自Android - ListView to load more items when reached end
您可以在listView上添加一个页脚，该页脚将有一个名为LoadMore的按钮。这是一个完整的教程List With Load more或者你可以实现onscrolllistener（）并将这个监听器添加到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's been a scroll which has completed ***/
/*** do the work for load more date! ***/
if(!isLoading){
isLoading = true;
loadMoreData();
}
}
}
答案 2 :(得分：0)
嗨@carefree这里有一个解决方案可能会让你完全达到你想要的目标 https://github.com/rahulinaction/ImageGrid
答案 3 :(得分：0)
最可能出现在您的任务和适配器上的问题，而不是列表滚动。 您可以在listAdapter中实现方法addItems，如下所示：
public void addItems(BusniessListData... newItems){
for(BusniessListData newItem : newItems){
this.businesses.add(newItem);
}
notifyDataSetChanged();
}
在你的任务的onPostExecute或你使用的任何回调中，检查listAdapter是否有项目，然后调用addItems传递新获取的项目。否则，启动并填充提取的数据集。