我一直在研究一个Android项目，我需要从服务器获取数据并在列表视图中显示。第一次检索成功完成，但从第二次检索开始，所取出的数据被放置在先前获取的数据之下。如何刷新列表视图以查看列表视图中的提取数据？我使用的代码如下。
package com.example.sohan.patient;
import android.app.Fragment;
import android.app.FragmentManager;
import android.app.FragmentTransaction;
import android.content.Context;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.BaseAdapter;
import android.widget.Button;
import android.widget.ListView;
import android.widget.Spinner;
import android.widget.TextView;
import android.widget.Toast;
import org.json.JSONArray;
import org.json.JSONObject;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLEncoder;
import java.util.ArrayList;
import java.util.List;
/**
* Created by Sohan on 5/20/2016.
*/
public class Doctors_layout extends Fragment implements AdapterView.OnItemSelectedListener{
View myView;
Spinner spinner;
String selectedCity;
Context myContext;
String jsonResult;
JSONObject jsonObject;
JSONArray jsonArray;
ContactAdapter contactAdapter;
String JSON_String;
ListView listView;
Button button;
int check=0;
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
myView = inflater.inflate(R.layout.doctors_directory, container, false);
myContext = inflater.getContext();
contactAdapter = new ContactAdapter(myContext, R.layout.row_layout);
spinner = (Spinner)myView.findViewById(R.id.spinner);
listView = (ListView)myView.findViewById(R.id.listView);
listView.setAdapter(contactAdapter);
spinner.setOnItemSelectedListener(this);
List<String> city = new ArrayList<String>();
city.add("Choose a City");
city.add("Chittagong");
city.add("Dhaka");
ArrayAdapter<String> aAdapter = new ArrayAdapter<String>(myContext, android.R.layout.simple_spinner_item ,city);
aAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spinner.setAdapter(aAdapter);
return myView;
}
@Override
public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
//contactAdapter.notifyDataSetChanged();
if(check==0) {
((TextView) parent.getChildAt(0)).setTextSize(21);
if (position == 0) {
nothing();
} else {
check++;
selectedCity = parent.getItemAtPosition(position).toString();
Toast.makeText(myContext, "Check value: "+check, Toast.LENGTH_LONG).show();
retrieveInfo ri = new retrieveInfo();
ri.execute(selectedCity); // notifydata
}
}
else{
contactAdapter.notifyDataSetChanged();
selectedCity = parent.getItemAtPosition(position).toString();
retrieveInfo ri = new retrieveInfo();
ri.execute(selectedCity);
}
}
@Override
public void onNothingSelected(AdapterView<?> parent) {
}
public void nothing(){
//Toast.makeText(myContext, "Default position 0", Toast.LENGTH_LONG).show();
}
class retrieveInfo extends AsyncTask<String, Void, String> { // send data to server
String myUrl;
protected void onPreExecute() {
myUrl ="http://bdpricelist.com/patient/retrieveMedicalName.php"; // change php script
}
protected String doInBackground(String... args) {
String city;
String result = null;
city = args[0];
JSONArray jsonArray = null;
try{
URL url = new URL(myUrl);
HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
httpURLConnection.setRequestMethod("POST");
httpURLConnection.setDoOutput(true);
OutputStream outputStream = httpURLConnection.getOutputStream();
BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(outputStream, "UTF-8"));
String data_to_send = URLEncoder.encode("city", "UTF-8")+"="+URLEncoder.encode(city,"UTF-8");
bufferedWriter.write(data_to_send);
bufferedWriter.flush();
bufferedWriter.close();
outputStream.close();
InputStream is = httpURLConnection.getInputStream();
BufferedReader reader = new BufferedReader(new InputStreamReader(is, "UTF-8"), 8);
StringBuilder sb = new StringBuilder();
while ((JSON_String = reader.readLine()) != null)
{
sb.append(JSON_String+"\n");
}
reader.close();
httpURLConnection.disconnect();
is.close();
return sb.toString().trim();
}catch(MalformedURLException e){
e.printStackTrace();
}catch(IOException f){
f.printStackTrace();
}
return null;
}
protected void onPostExecute(String result) {
jsonResult = result;
parseJSON(jsonResult);
//jsonResult="";
}
}
public void delete(String city) {
Fragment Dl = new Doctors_layout();
FragmentTransaction fragmentTransaction = getFragmentManager().beginTransaction();
fragmentTransaction.replace(R.id.content_frame, Dl);
fragmentTransaction.addToBackStack(null);
fragmentTransaction.commit();
}
public void parseJSON(String json){
Contacts contacts=null;
try {
jsonObject = new JSONObject(json);
jsonArray = jsonObject.getJSONArray("patient");
int count = 0;
String name;
while (count < jsonArray.length()) {
JSONObject jo = jsonArray.getJSONObject(count);
name = jo.getString("Medical"); // data's are send to store in and print in listview
contacts = new Contacts(name);
contactAdapter.add(contacts);
count++;
}
//contactAdapter.add(contacts.getMedicalName());
} catch (Exception e) {
e.printStackTrace();
}
}
}
And my adapter class is given below
package com.example.sohan.patient;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.BaseAdapter;
import android.widget.TextView;
import android.widget.Toast;
import java.util.ArrayList;
import java.util.List;
/**
* Created by Sohan on 6/9/2016.
*/
public class ContactAdapter extends ArrayAdapter {
//ContactHolder contactHolder;
List list = new ArrayList();
ContactAdapter contactAdapter;
List receivedList = new ArrayList();
View row;
ContactHolder contactHolder;
int count =0;
public ContactAdapter(Context context, int resource) {
super(context, resource);
}
public void add(Contacts object) {
// list.clear();
super.add(object);
list.add(object);
//notifyDataSetChanged();
Toast.makeText(getContext().getApplicationContext(), "Entry without delete ", Toast.LENGTH_SHORT).show();
}
@Override
public int getCount() {
return list.size();
}
@Override
public void clear() {
super.clear();
}
@Override
public boolean isEmpty() {
return super.isEmpty();
}
@Override
public void notifyDataSetChanged() {
super.notifyDataSetChanged();
}
public void deleteEntry(){
list.clear();
Toast.makeText(getContext().getApplicationContext(), "List cleared before entry ", Toast.LENGTH_SHORT).show();
}
@Override
public Object getItem(int position) {
return list.get(position);
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
//count++;
row = convertView;
if(row==null){
LayoutInflater layoutInflater = (LayoutInflater)this.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
row = layoutInflater.inflate(R.layout.row_layout,parent,false);
contactHolder = new ContactHolder();
contactHolder.MedicalName =(TextView) row.findViewById(R.id.textView5);
row.setTag(contactHolder);
}
else{
contactHolder = (ContactHolder)row.getTag();
}
contactHolder = new ContactHolder();
contactHolder.MedicalName =(TextView) row.findViewById(R.id.textView5);
Contacts contacts = (Contacts)this.getItem(position);
contactHolder.MedicalName.setText(contacts.getMedicalName());
return row;
}
static class ContactHolder{
TextView MedicalName;
}
}
答案 0 :(得分：0)
新数据显示在旧数据之后，因为您要将新数据添加到parseJSON()中的现有数据。
如果您要使用新数据替换旧数据，请从onCreateView删除这些行，并在parseJSON()循环后立即添加到while内。
contactAdapter = new ContactAdapter(myContext, R.layout.row_layout);
listView.setAdapter(contactAdapter);
答案 1 :(得分：0)
不要在适配器中添加（Contacts对象），而是使用一种方法清除列表中的当前项并使用新检索的项进行更新。
private void updateContactList(List<Contacts> updatedList) {
list.clear();
list.addAll(updatedList);
notifyDataSetChanged();
}
和parseJSON（String json）内部
List<Contacts> newList = new ArrayList<>();
while (count < jsonArray.length()) {
JSONObject jo = jsonArray.getJSONObject(count);
name = jo.getString("Medical");
contacts = new Contacts(name);
newList.add(contacts);
count++;
}
contactAdapter.updateContactList(newList);