在我的代码中，我希望在每 10秒后定期更新ListView 。由于ListView是自定义的，ListView中的数据是从数据库填充的，因此我需要定期刷新ListView，以便数据库中的任何更改都可以反映在ListView中。我尝试使用Handler概念，但它没有帮助我。以下是我的代码。需要做什么？
public class GetFriendDeviceId extends ListActivity {
String data = "";
String title;
ListView list;
CustomDeviceId adapter;
ArrayList<String> useridarr;
ArrayList<String> namearr;
ArrayList<String> regidarr;
ArrayList<String> statusarr;
String id;
String userid, name, regid;
private static final String USERID = "user_id";
private static final String NAME = "user_name";
private static final String REGID = "regId";
DBController contoller = new DBController(this);
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.getfriend_deviceid);
useridarr = new ArrayList<String>();
namearr = new ArrayList<String>();
regidarr = new ArrayList<String>();
statusarr = new ArrayList<String>();
// get user_id using sharedpreference
SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(getBaseContext());
id = preferences.getString("ID", "");
new GetContent().execute();
}
// asynctask to get content for selected title
public class GetContent extends AsyncTask<Void, Void, Void>
{
ProgressDialog pdLoading = new ProgressDialog(GetFriendDeviceId.this);
@Override
protected void onPreExecute() {
super.onPreExecute();
useridarr.clear();
namearr.clear();
regidarr.clear();
statusarr.clear();
pdLoading.setMessage("\tPlease wait...");
pdLoading.show();
}
@Override
protected Void doInBackground(Void... params) {
final GetDeviceId getdb = new GetDeviceId();
new Thread(new Runnable() {
public void run() {
data = getdb.getDataFromDB(id);
System.out.println(data);
runOnUiThread(new Runnable() {
@Override
public void run() {
ArrayList<User_DeviceId> users = parseJSON(data);
addData(users);
}
});
}
}).start();
return null;
}
@Override
protected void onPostExecute(Void result) {
super.onPostExecute(result);
pdLoading.dismiss();
}
}
public ArrayList<User_DeviceId> parseJSON(String result) {
ArrayList<User_DeviceId> users = new ArrayList<User_DeviceId>();
try
{
JSONArray jArray = new JSONArray(result);
for (int i = 0; i < jArray.length(); i++)
{
JSONObject json_data = jArray.getJSONObject(i);
User_DeviceId user = new User_DeviceId();
user.setUser_id(json_data.getString(USERID));
user.setUser_name(json_data.getString(NAME));
user.setRegId(json_data.getString(REGID));
users.add(user);
}
} catch (JSONException e) {
Log.e("log_tag", "Error parsing data " + e.toString());
}
return users;
}
@SuppressWarnings({ "rawtypes" })
public void addData(ArrayList<User_DeviceId> users) {
for (Iterator i = users.iterator(); i.hasNext();) {
User_DeviceId p = (User_DeviceId) i.next();
useridarr.add(p.getUser_id());
namearr.add(p.getUser_name());
regidarr.add(p.getRegId());
}
DBController.statusArray = statusarr;
contoller.getStatus(id, useridarr, 0);
adapter = new CustomDeviceId(GetFriendDeviceId.this, namearr, useridarr, statusarr);
list.setAdapter(adapter);
}
我试过这段代码
final Handler handler_new = new Handler();
handler_new.postDelayed( new Runnable() {
@Override
public void run() {
DBController.statusArray = MainActivity.result;
contoller.Status("100003818200590", "100007144268382", 0);
MainActivity.adapter.notifyDataSetChanged();
handler_new.postDelayed( this, 1000);
}
}, 1000);
但是没有用......
答案 0 :(得分：2)
我只是编辑您的代码希望这可以帮助您
import java.util.ArrayList;
import java.util.Iterator;
import java.util.Timer;
import java.util.TimerTask;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.app.ListActivity;
import android.app.ProgressDialog;
import android.content.SharedPreferences;
import android.os.AsyncTask;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.util.Log;
import android.widget.ListView;
public class GetFriendDeviceId extends ListActivity {
String data = "";
String title;
ListView list;
CustomDeviceId adapter;
ArrayList<String> useridarr;
ArrayList<String> namearr;
ArrayList<String> regidarr;
ArrayList<String> statusarr;
String id;
String userid, name, regid;
private static final String USERID = "user_id";
private static final String NAME = "user_name";
private static final String REGID = "regId";
DBController contoller;
Timer timer;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.getfriend_deviceid);
contoller = new DBController(this);
useridarr = new ArrayList<String>();
namearr = new ArrayList<String>();
regidarr = new ArrayList<String>();
statusarr = new ArrayList<String>();
// get user_id using sharedpreference
SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(getBaseContext());
id = preferences.getString("ID", "");
timer = new Timer();
timer.schedule(new TimerTask() {
@Override
public void run() {
runOnUiThread(new Runnable() {
@Override
public void run() {
new GetContent().execute();
}
});
}
}, 0, 10000);
}
// asynctask to get content for selected title
public class GetContent extends AsyncTask<Void, Void, ArrayList<User_DeviceId>> {
ProgressDialog pdLoading = new ProgressDialog(GetFriendDeviceId.this);
@Override
protected void onPreExecute() {
super.onPreExecute();
useridarr.clear();
namearr.clear();
regidarr.clear();
statusarr.clear();
pdLoading.setMessage("\tPlease wait...");
pdLoading.show();
}
@Override
protected ArrayList<User_DeviceId> doInBackground(Void... params) {
final GetDeviceId getdb = new GetDeviceId();
data = getdb.getDataFromDB(id);
ArrayList<User_DeviceId> users = parseJSON(data);
return users;
}
@Override
protected void onPostExecute(ArrayList<User_DeviceId> result) {
super.onPostExecute(result);
addData(result);
pdLoading.dismiss();
}
}
public ArrayList<User_DeviceId> parseJSON(String result) {
ArrayList<User_DeviceId> users = new ArrayList<User_DeviceId>();
try {
JSONArray jArray = new JSONArray(result);
for (int i = 0; i < jArray.length(); i++) {
JSONObject json_data = jArray.getJSONObject(i);
User_DeviceId user = new User_DeviceId();
user.setUser_id(json_data.getString(USERID));
user.setUser_name(json_data.getString(NAME));
user.setRegId(json_data.getString(REGID));
users.add(user);
}
} catch (JSONException e) {
Log.e("log_tag", "Error parsing data " + e.toString());
}
return users;
}
@SuppressWarnings({ "rawtypes" })
public void addData(ArrayList<User_DeviceId> users) {
for (Iterator i = users.iterator(); i.hasNext();) {
User_DeviceId p = (User_DeviceId) i.next();
useridarr.add(p.getUser_id());
namearr.add(p.getUser_name());
regidarr.add(p.getRegId());
}
DBController.statusArray = statusarr;
contoller.getStatus(id, useridarr, 0);
adapter = new CustomDeviceId(GetFriendDeviceId.this, namearr, useridarr, statusarr);
list.setAdapter(adapter);
}
}
答案 1 :(得分：1)
不断/定期轮询改变通常不是一个好主意。
在更新数据库以获得更好的性能时，您应该执行推送通知之类的操作。当一段代码更改了DB的内容时，它应该调用所有侦听器订阅者/或者广播消息。
您的活动/片段应该实现该侦听器，并刷新列表视图。这样，只有在DB中发生某些更改而不是在DB中查找更改并自行刷新时，才会刷新列表视图。
A listview can be refreshed by modifying the backing datasource of listview.
namearr = newnamearr;
...
newnamearr是listview的新内容。
然后拨打notifyDataSetChanged()。
这段代码正在运行，但它们可能是更好的方法。 import java.util.ArrayList;
public class ListenerTest {
public static void main(String[] args) {
// simulation for activities.
A a = new A();
a.simulateOnCreate();
B b = new B();
b.simulateOnCreate();
DBChanger obj = new DBChanger();
obj.changeDBContent();
}
}
// this is class where all DB changes will occur.
class DBChanger{
public void changeDBContent(){
// some piece of Code that change the DB code.
ArrayList<Listenable> subcribers = ListnerManager.getInstance().getSubscribersList();
for(Listenable l: subcribers){
l.onUpadateAvailable();
}
}
}
// This class should corresponds to Activity/Fragment in Android which will implement the listener
class A implements Listenable {
public void simulateOnCreate(){
ListnerManager maneger = ListnerManager.getInstance();
maneger.setOnListenable(this);
}
@Override
public void onUpadateAvailable() {
System.out.println("A---> onUpadateAvailable");
}
}
// This class is manager of listener.
class ListnerManager {
public static ListnerManager instance = new ListnerManager();
public static ListnerManager getInstance(){
if(instance == null){
instance = new ListnerManager();
}
return instance;
}
ArrayList<Listenable> subscriberlist = new ArrayList<Listenable>();
public void setOnListenable(Listenable subcsriber) {
subscriberlist.add(subcsriber);
}
public ArrayList<Listenable> getSubscribersList() {
return subscriberlist;
}
}
// Same as class A
class B implements Listenable {
public void simulateOnCreate(){
ListnerManager maneger = ListnerManager.getInstance();
maneger.setOnListenable(this);
}
@Override
public void onUpadateAvailable() {
// TODO Auto-generated method stub
System.out.println("B---> onUpadateAvailable");
}
}
interface Listenable {
public void onUpadateAvailable();
}
我在控制台上收到的输出：
A---> onUpadateAvailable
B---> onUpadateAvailable
答案 2 :(得分：0)
我同意@GauravGupta。最好的方法是在数据库发生更改时实现推送通知。
但是关于你的问题，你可以尝试运行这个asynctask：
class refreshList extends AsyncTask<String, String, String> {
Context context
public refreshList(Context context){
this.context=context;
@Override
protected String doInBackground(String... params) {
// TODO Auto-generated method sstub
Timer timer = new Timer();
timer.scheduleAtFixedRate(new TimerTask() {
@Override
public void run() {
// TODO Auto-generated method stub
//Since you cant invoke notify notifyDataSetChanged() inside the doInBackground. So we will use this code:
((MainActivity) context).runOnUiThread(new Runnable() {
public void run() {
//Do your code here like refreshing your adapter
MainActivity.adapter.notifyDataSetChanged();
//
}
});
}
}, 1000, 10000);
//1000= interval delay;
//10000= run every 10secs
return null;
}
}
请记住在运行asynctask时传递活动的上下文。 new refreshList（this）.execute（）;