当我通过api从web加载数据时，用户在listview中滚动到底部，但是当我在listview上滚动一次时，它在我的活动中多次调用asynctask，导致listview中的重复数据，并且在异常情况下很多关于活动的对话和祝酒，当我滚动到底部并且只是在滚动方法上触摸我的列表视图时会再次调用asynctask很多次，所以请告诉我如何防止这种情况。
这是我的onscroll方法代码。
listView.setOnScrollListener(new OnScrollListener() {
// boolean mIsScrollingUp;
// int mLastFirstVisibleItem;
@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
// TODO Auto-generated method stub
if(scrollState == OnScrollListener.SCROLL_STATE_TOUCH_SCROLL)
userscrolled=true;
}
@Override
public void onScroll(AbsListView view, int firstVisibleItem,
int visibleItemCount, int totalItemCount) {
// TODO Auto-generated method stub
int lasinscren = firstVisibleItem + visibleItemCount;
if(userscrolled&&(lasinscren==totalItemCount)&&!lodinmore&&(visibleItemCount<totalItemCount)&&havedata)
{
progress = true;
if(Search_API==false){
if(connectionDetector.isConnectintoInternet()){
System.out.println("inside listview on scroll function");
darList_task = new DAR_list_task(DAR_Activity.this).execute();
lodinmore = true;
}else
{
Toast.makeText(getApplicationContext(), "No internet connection", Toast.LENGTH_SHORT).show();
}
}else
{
new search_task(DAR_Activity.this).execute();
}
}
}
});
这是我的asynctask
public class DAR_list_task extends AsyncTask<Void, Void, Void>
{
Context activity;
public DAR_list_task(Context activity) {
// TODO Auto-generated constructor stub
this.activity = activity;
}
@Override
protected void onPreExecute() {
// TODO Auto-generated method stub
super.onPreExecute();
if(progress==true){
if(limit==0)
{
dialog = new Dialog(DAR_Activity.this);
dialog.getWindow().requestFeature(Window.FEATURE_NO_TITLE);
dialog.getWindow().setBackgroundDrawable(new ColorDrawable(Color.TRANSPARENT));
LinearLayout linearLayout = (LinearLayout)getLayoutInflater().inflate(R.layout.dialog_progress, null);
dialog.setContentView(linearLayout);
ProgressBar progressBar1 = (ProgressBar)findViewById(R.id.progress_dialog);
dialog.setCancelable(false);
dialog.getWindow().clearFlags(WindowManager.LayoutParams.FLAG_DIM_BEHIND);
dialog.setCanceledOnTouchOutside(false);
dialog.show();
dialog.getWindow().setGravity(Gravity.CENTER);
}else
{
progressBar.setVisibility(View.VISIBLE);
}
}
}
@Override
protected Void doInBackground(Void... params) {
// TODO Auto-generated method stub
response=null;
lodinmore = true;
URL Url;
try {
byte[] data;
data = login_id.getBytes("UTF-8");
String login_base_64 = Base64.encode(data);
data = gcm_id.getBytes("UTF-8");
String gcm_base64= Base64.encode(data);
if(url.contentEquals(""))
{
Url = new URL(getResources().getString(R.string.dar_list_view));
}else
{
Url = new URL("http://"+url+"/smart_oms/dar_app/view_dar.php");
}
List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
nameValuePairs.add(new BasicNameValuePair("login_id", login_base_64));
nameValuePairs.add(new BasicNameValuePair("gcm_id", gcm_base64));
nameValuePairs.add(new BasicNameValuePair("limit", String.valueOf(limit)));
HttpURLConnection httpURLConnection = (HttpURLConnection)Url.openConnection();
httpURLConnection.setRequestMethod("POST");
httpURLConnection.setUseCaches(false);
httpURLConnection.setDoOutput(true);
OutputStream os = httpURLConnection.getOutputStream();
BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(os, "UTF-8"));
bufferedWriter.write(getQueryString(nameValuePairs));
bufferedWriter.flush();
bufferedWriter.close();
os.close();
httpURLConnection.connect();
InputStream inputStream = httpURLConnection.getInputStream();
response = BufferReaderMaker.readContentFromIS(inputStream);
}catch( final UnknownHostException ex)
{
runOnUiThread(new Runnable() {
public void run() {
Toast.makeText(getApplicationContext(), ex.getMessage(), Toast.LENGTH_SHORT).show();
}
});
}catch (final ConnectTimeoutException e) {
// TODO: handle exception
runOnUiThread(new Runnable() {
public void run() {
Toast.makeText(getApplicationContext(), e.getMessage(), Toast.LENGTH_SHORT).show();
}
});
}
catch (Exception e) {
// TODO: handle exception
}
return null;
}
@Override
protected void onPostExecute(Void result) {
// TODO Auto-generated method stub
super.onPostExecute(result);
Object json = null;
try {
if(response!=null)
{
if(progress==false)
{
dar_List_Items.clear();
dar_Aadapter = new DAR_Aadapter(DAR_Activity.this, dar_List_Items);
listView.setAdapter(dar_Aadapter);
dar_Aadapter.notifyDataSetChanged();
}
try {
json = new JSONTokener(response).nextValue();
} catch (JSONException e1) {
// TODO Auto-generated catch block
ErrorDialog errorDialog = new ErrorDialog();
errorDialog.Dialog(activity, statusCode, response, login_id, "", new DAR_list_task(activity));
}
if(json instanceof JSONArray)
{
havedata=false;
Toast.makeText(getApplicationContext(), "No More DAR", 0).show();
}else if(json instanceof JSONObject)
{
JSONObject jsonObject = new JSONObject(response);
JSONArray jsonArray = jsonObject.getJSONArray("view_dar_detail");
for(int i =0 ;i<jsonArray.length();)
{
JSONObject json_data = jsonArray.getJSONObject(i);
String dar_id = json_data.optString("customer_id");
String Customer_name = json_data.optString("customer_name");
String Contacted= json_data.optString("contact_person_name");
String product = json_data.optString("product");
String status = json_data.optString("dar_status");
String Contact_type = json_data.optString("contact_type");
String created_date = json_data.optString("dar_created_date");
String request_date = json_data.optString("requeste_date");
DAR_List_Item dar_List_Item = new DAR_List_Item(dar_id,Customer_name, Contacted, Contact_type, product, status, created_date, request_date,"abcd");
dar_List_Items.add(dar_List_Item);
i++;
}
int index = listView.getFirstVisiblePosition();
View v= listView.getChildAt(0);
int top = (v == null) ? 0 : v.getTop();
listView.setAdapter(null);
DAR_Aadapter aadapter = new DAR_Aadapter(DAR_Activity.this, dar_List_Items);
listView.setAdapter(aadapter);
aadapter.notifyDataSetChanged();
listView.setSelectionFromTop(index, top);
}else
{
ErrorDialog errorDialog = new ErrorDialog();
errorDialog.Dialog(activity, statusCode, response, login_id, "", new DAR_list_task(activity));
}
lodinmore = false;
}
lodinmore = false;
} catch (JSONException e) {
// TODO Auto-generated catch block
ErrorDialog errorDialog = new ErrorDialog();
errorDialog.Dialog(activity, statusCode, response, login_id, "", new DAR_list_task(activity));
}
if(progress==true){
if(limit==0)
{
dialog.dismiss();
}else{
progressBar.setVisibility(View.GONE);
}
}
if(json instanceof JSONObject)
limit = limit +10;
}
}
pLease帮助我，我已经尝试了很多东西，比如使用旗帜值等等，但不是为我工作。
如何防止多次调用asynctask调用？ 当我滚动到底部并只触摸列表时，如何防止asynctask被触发？
答案 0 :(得分：1)
有一个解决方法：
final int lastItem = firstVisibleItem + visibleItemCount;
if(lastItem == totalItemCount) {
if(lastLastitem !=lastItem){ //to avoid multiple calls for last item, declare it as a field in your Activity
lastLastitem = lastItem;
// Your async task here
}
答案 1 :(得分：0)
一种简单的方法是定义一个布尔参数：
if(view.getLastVisiblePosition() == totalItemCount-1 && isLoadMore){
isLoadMore = false;
pageNum++;
loadMoreData(searchStr, donViID, pageNum, Constant.RECORD_PER_PAGE);
}