Java 当我按下“后退”按钮时,如何停止再次加载ListView?
我创建了一个包含三个活动的Android应用程序,MainActivity-->SongActivity-->DownloadActivity。MainActivity和SongActivity是从mysql数据库获取项目列表的列表视图。当我通过按后退按钮从SongActivity导航回MainActivity时,ListView会再次获取数据,这使得应用程序导航速度变慢。有解决办法吗 MainActivity.javaJava 当我按下“后退”按钮时,如何停止再次加载ListView?,java,android,mysql,listview,android-listview,Java,Android,Mysql,Listview,Android Listview,我创建了一个包含三个活动的Android应用程序,MainActivity-->SongActivity-->DownloadActivity。MainActivity和SongActivity是从mysql数据库获取项目列表的列表视图。当我通过按后退按钮从SongActivity导航回MainActivity时,ListView会再次获取数据,这使得应用程序导航速度变慢。有解决办法吗 MainActivity.java package com.example.telugump3; import
package com.example.telugump3;
import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONArray;
import org.json.JSONObject;
import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ListView;
import android.widget.TextView;
public class MainActivity extends Activity{
Activity context;
HttpPost httppost;
StringBuffer buffer;
HttpResponse response;
HttpClient httpclient;
ProgressDialog pd;
CustomAdapter adapter;
ListView listProduct;
ArrayList<String> records;
protected void onCreate(Bundle savedInstanceState) {
//TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
context=this;
records=new ArrayList<String>();
listProduct=(ListView)findViewById(R.id.product_list);
adapter=new CustomAdapter(context, R.layout.list_item,R.id.pro_name, records);
listProduct.setAdapter(adapter);
listProduct.setOnItemClickListener(new OnItemClickListener(){
@Override
public void onItemClick(AdapterView<?> arg0, View v, int position, long id){
String sText = ((TextView) v.findViewById(R.id.pro_name)).getText().toString();
Intent songIntent = new Intent(getApplicationContext(), SongActivity.class);
songIntent.putExtra("movie_name", sText );
startActivity(songIntent);
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.main, menu);
//create a LayoutTransition object
return true;
}
public void onStart(){
super.onStart();
//execute background task
BackTask bt=new BackTask();
bt.execute();
}
//background process to make a request to server and list product information
private class BackTask extends AsyncTask<Void,Void,Void>{
protected void onPreExecute(){
super.onPreExecute();
pd = new ProgressDialog(context);
pd.setTitle("Retrieving data");
pd.setMessage("Please wait.");
pd.setCancelable(true);
pd.setIndeterminate(true);
pd.show();
}
protected Void doInBackground(Void...params){
InputStream is=null;
String result="";
try{
records.clear();
httpclient=new DefaultHttpClient();
httppost= new HttpPost("http://necrecords.16mb.com/getproducts.php");
response=httpclient.execute(httppost);
HttpEntity entity = response.getEntity();
is = entity.getContent();
}catch(Exception e){
if(pd!=null)
pd.dismiss(); //close the dialog if error occurs
Log.e("ERROR",e.getMessage());
}
//convert response to string
try{
BufferedReader reader = new BufferedReader(new InputStreamReader(is,"utf-8"),8);
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
is.close();
result=sb.toString();
}catch(Exception e){
Log.e("ERROR", "Error converting result "+e.toString());
}
//parse json data
try{
JSONArray jArray =new JSONArray(result);
for(int i=0;i<jArray.length();i++){
JSONObject json_data = jArray.getJSONObject(i);
String record=json_data.getString("pname")+"__"+json_data.getInt("uprice");
records.add(record);
}
}
catch(Exception e){
Log.e("ERROR", "Error pasting data "+e.toString());
}
return null;
}
protected void onPostExecute(Void result){
if(pd!=null) pd.dismiss(); //close dialog
adapter.notifyDataSetChanged(); //notify the ListView to get new records
}
}
}
package com.example.telugump3;
import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.URLEncoder;
import java.util.ArrayList;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONArray;
import org.json.JSONObject;
import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.AdapterView;
import android.widget.ListView;
import android.widget.TextView;
public class SongActivity extends Activity{
Activity context;
HttpPost httppost;
StringBuffer buffer;
HttpResponse response;
HttpClient httpclient;
ProgressDialog pd;
CustomAdapter adapter;
ListView listProduct;
ArrayList<String> records;
String mname;
protected void onCreate(Bundle savedInstanceState) {
//TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.song_activity);
context=this;
records=new ArrayList<String>();
listProduct=(ListView)findViewById(R.id.product_list);
adapter=new CustomAdapter(context, R.layout.newlist_item,R.id.pro_name, records);
listProduct.setAdapter(adapter);
TextView songtitle = (TextView)findViewById(R.id.movietitle);
Intent iin= getIntent();
Bundle b = iin.getExtras();
if(b!=null)
{
mname =(String) b.getString("movie_name");
songtitle.setText(mname);
}
listProduct.setOnItemClickListener(new OnItemClickListener(){
@Override
public void onItemClick(AdapterView<?> arg0, View v, int position, long id){
String sText = ((TextView) v.findViewById(R.id.pro_name)).getText().toString();
Intent songIntent = new Intent(getApplicationContext(), DownloadActivity.class);
songIntent.putExtra("song_name", sText );
startActivity(songIntent);
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.main, menu);
//create a LayoutTransition object
return true;
}
public void onStart(){
super.onStart();
//execute background task
BackTask bt=new BackTask();
bt.execute();
}
//background process to make a request to server and list product information
private class BackTask extends AsyncTask<Void,Void,Void>{
protected void onPreExecute(){
super.onPreExecute();
pd = new ProgressDialog(context);
pd.setTitle("Retrieving data");
pd.setMessage("Please wait.");
pd.setCancelable(true);
pd.setIndeterminate(true);
pd.show();
}
protected Void doInBackground(Void...params){
InputStream is=null;
String result="";
try{
records.clear();
String query = URLEncoder.encode(mname, "utf-8");
httpclient=new DefaultHttpClient();
httppost= new HttpPost("http://necrecords.16mb.com/getsongslist.php?password="+query);
response=httpclient.execute(httppost);
HttpEntity entity = response.getEntity();
is = entity.getContent();
}catch(Exception e){
if(pd!=null)
pd.dismiss(); //close the dialog if error occurs
Log.e("ERROR",e.getMessage());
}
//convert response to string
try{
BufferedReader reader = new BufferedReader(new InputStreamReader(is,"utf-8"),8);
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
is.close();
result=sb.toString();
}catch(Exception e){
Log.e("ERROR", "Error converting result "+e.toString());
}
//parse json data
try{
JSONArray jArray =new JSONArray(result);
for(int i=0;i<jArray.length();i++){
JSONObject json_data = jArray.getJSONObject(i);
String record=json_data.getString("allsongs")+"__"+json_data.getString("test");
records.add(record);
}
}
catch(Exception e){
Log.e("ERROR", "Error pasting data "+e.toString());
}
return null;
}
protected void onPostExecute(Void result){
if(pd!=null) pd.dismiss(); //close dialog
adapter.notifyDataSetChanged(); //notify the ListView to get new records
}
}
}
package com.example.telugump3;
导入java.io.BufferedReader;
导入java.io.InputStream;
导入java.io.InputStreamReader;
导入java.util.ArrayList;
导入org.apache.http.HttpEntity;
导入org.apache.http.HttpResponse;
导入org.apache.http.client.HttpClient;
导入org.apache.http.client.methods.HttpPost;
导入org.apache.http.impl.client.DefaultHttpClient;
导入org.json.JSONArray;
导入org.json.JSONObject;
导入android.app.Activity;
导入android.app.ProgressDialog;
导入android.content.Intent;
导入android.os.AsyncTask;
导入android.os.Bundle;
导入android.util.Log;
导入android.view.Menu;
导入android.view.view;
导入android.widget.AdapterView;
导入android.widget.AdapterView.OnItemClickListener;
导入android.widget.ListView;
导入android.widget.TextView;
公共类MainActivity扩展了活动{
活动语境;
HttpPost-HttpPost;
字符串缓冲区;
HttpResponse响应;
HttpClient-HttpClient;
进展性帕金森病;
自定义适配器;
ListView listProduct;
ArrayList记录;
创建时受保护的void(Bundle savedInstanceState){
//TODO自动生成的方法存根
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
上下文=这个;
记录=新的ArrayList();
listProduct=(ListView)findViewById(R.id.product\u列表);
adapter=新的CustomAdapter(上下文、R.layout.list\u项、R.id.pro\u名称、记录);
setAdapter(适配器);
setOnItemClickListener(新的OnItemClickListener(){
@凌驾
public void onItemClick(AdapterView arg0,视图v,内部位置,长id){
字符串sText=((TextView)v.findviewbyd(R.id.pro_name)).getText().toString();
Intent songIntent=新的Intent(getApplicationContext(),SongActivity.class);
songIntent.putExtra(“电影名称”,sText);
星触觉(songIntent);
}
});
}
@凌驾
公共布尔onCreateOptions菜单(菜单){
getMenuInflater().充气(R.menu.main,menu);
//创建LayoutTransition对象
返回true;
}
public void onStart(){
super.onStart();
//执行后台任务
BackTask bt=新的BackTask();
bt.execute();
}
//向服务器发出请求并列出产品信息的后台进程
私有类BackTask扩展了AsyncTask{
受保护的void onPreExecute(){
super.onPreExecute();
pd=新进度对话框(上下文);
pd.setTitle(“检索数据”);
设置消息(“请稍候”);
pd.可设置可取消(真);
pd.SetUndeterminate(真);
pd.show();
}
受保护的Void doInBackground(Void…params){
InputStream=null;
字符串结果=”;
试一试{
记录。清除();
httpclient=新的DefaultHttpClient();
httppost=新的httppost(“http://necrecords.16mb.com/getproducts.php");
response=httpclient.execute(httppost);
HttpEntity=response.getEntity();
is=entity.getContent();
}捕获(例外e){
如果(pd!=null)
pd.disclose();//如果发生错误,请关闭对话框
Log.e(“ERROR”,e.getMessage());
}
//将响应转换为字符串
试一试{
BufferedReader reader=新的BufferedReader(新的InputStreamReader(is,“utf-8”),8;
StringBuilder sb=新的StringBuilder();
字符串行=null;
而((line=reader.readLine())!=null){
sb.追加(第+行“\n”);
}
is.close();
结果=sb.toString();
}捕获(例外e){
Log.e(“错误”,“错误转换结果”+e.toString());
}
//解析json数据
试一试{
JSONArray jArray=新JSONArray(结果);
对于(int i=0;i请添加
//执行后台任务
BackTask bt=new BackTask();
bt.execute();
在onCreate()
中,改为onStart()
上的onCreate()
欲了解更多信息,请查看
编辑
protected void onCreate(Bundle savedInstanceState) {
//TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
context=this;
records=new ArrayList<String>();
listProduct=(ListView)findViewById(R.id.product_list);
BackTask bt=new BackTask();
bt.execute();
adapter=new CustomAdapter(context, R.layout.list_item,R.id.pro_name, records);
listProduct.setAdapter(adapter);
listProduct.setOnItemClickListener(new OnItemClickListener(){
@Override
public void onItemClick(AdapterView<?> arg0, View v, int position, long id){
String sText = ((TextView) v.findViewById(R.id.pro_name)).getText().toString();
Intent songIntent = new Intent(getApplicationContext(), SongActivity.class);
songIntent.putExtra("movie_name", sText );
startActivity(songIntent);
}
});
}
创建时受保护的void(Bundle savedInstanceState){
//TODO自动生成的方法存根
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
上下文=这个;
记录=新的ArrayList();
listProduct=(ListView)findViewById(R.id.product\u列表);
BackTask bt=新的BackTask();
bt.execute();
adapter=新的CustomAdapter(上下文、R.layout.list\u项、R.id.pro\u名称、记录);
setAdapter(适配器);
setOnItemClickListener(新的OnItemClickListener(){
@凌驾
public void onItemClick(AdapterView arg0,视图v,内部位置,长id){
字符串sText=((TextView)v.findviewbyd(R.id.pro_name)).getText().toString();
Intent songIntent=新的Intent(getApplicationContext(),SongActivity.class);
songIntent.putExtra(“电影名称”,sText);
星触觉(songIntent);
}
});
}
在远程检查数据时,让您的活动做出更好响应的一种方法是使用onSaveInstanceState()缓存数据,并将记录列表保存在一个捆绑包中,您可以在活动的onCreate()期间从中读取
如果系统决定从堆栈中删除您的活动,那么它将尝试再次从远程主机加载数据(这可能需要一段时间)
也是的,您应该在onCreate()而不是onStart()中执行AsyncTask,并确保