从服务器 json 响应延迟加载 listview 项
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【中文标题】从服务器 json 响应延迟加载 listview 项【英文标题】：Lazy Load listview Item from server json response 【发布时间】：2015-07-25 14:45:21 【问题描述】：我正在开发一个 android 应用程序，它通过 json 解析器从服务器加载数据。我想从服务器加载 10 项部分中的数据，当用户向下滚动列表视图时，从服务器加载新的 10 项部分并添加到当前列表视图（例如市场应用程序）。
这里是java代码：
public class AllProductsActivity extends ListActivity
//jpcode
int part=0;
String refreshNumber="0";
//convert to shamsi
Roozh jCal = new Roozh();
String myjpdiff;
ImageButton btnNewProduct;
View ntCheck;
private SessionManager session;
private Button logout;
//internet check jp
// flag for Internet connection status
Boolean isInternetPresent = false;
// Connection detector class
ConnectionDetector cd;
//end internet check jp
private SQLiteHandler db; //jpcode
//end jpcode
// Progress Dialog
private ProgressDialog pDialog;
// Creating JSON Parser object
JSONParser jParser = new JSONParser();
ArrayList<HashMap<String, String>> productsList;
// url to get all products list
private static String url_all_products = "http://www.jpdesign.ir/android_login_api/ac/get_all_products.php";
// JSON Node names
private static final String TAG_SUCCESS = "success";
private static final String TAG_PRODUCTS = "products";
private static final String TAG_PID = "pid";
private static final String TAG_NAME = "name";
//jpcode
private static final String TAG_AUTH = "auth";
private static final String TAG_HIT = "hit";
private static final String TAG_DATE = "created_at";
private static final String TAG_JPTIME = "jptime";
private static final String TAG_JPPart = "part";
private TextView txtName;
// products JSONArray
JSONArray products = null;
Typeface jpfont;
public PullToRefreshListView listView;
@Override
public void onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState);
overridePendingTransition(R.anim.push_right_in,R.anim.push_right_out);
setContentView(R.layout.all_products);
jpfont = Typeface.createFromAsset(getAssets(), "fonts/yekan.ttf");
TextView fakeDate= (TextView) findViewById(R.id.textView1);
fakeDate.setTypeface(jpfont);
// SQLite database handler
db = new SQLiteHandler(getApplicationContext());
// session manager
session = new SessionManager(getApplicationContext()); //jpcode
//adding slidemenu
final SlidingMenu menu = new SlidingMenu(this);
menu.setMode(SlidingMenu.RIGHT);
menu.setTouchModeAbove(SlidingMenu.TOUCHMODE_FULLSCREEN);
menu.setShadowWidthRes(R.dimen.shadow_width);
menu.setShadowDrawable(R.drawable.shadowright);
menu.setBehindOffsetRes(R.dimen.slidingmenu_offset);
menu.setFadeDegree(0.35f);
menu.attachToActivity(this, SlidingMenu.SLIDING_CONTENT);
menu.setMenu(R.layout.slide_layout);
ImageButton iconfehrest = (ImageButton) findViewById(R.id.sliding);
// get name of user
// Fetching user details from sqlite
HashMap<String, String> user = db.getUserDetails();
String name = user.get("name");
String email = user.get("email");
txtName = (TextView) findViewById(R.id.mnt);
// Displaying the user details on the screen
Log.d("LOG", name +" and "+email);
txtName.setText(name);
//txtEmail.setText(email);
///end get name
iconfehrest.setOnClickListener(new View.OnClickListener()
@Override
public void onClick(View view)
menu.toggle();
);
//end slide menu
//jpcode
logout= (Button) findViewById(R.id.Ulogout);
logout.setOnClickListener(new View.OnClickListener()
@Override
public void onClick(View v)
logoutUser();
);
final View ntCheck = findViewById(R.id.net_check);
ntCheck.setVisibility(View.GONE);
// creating connection detector class instance
cd = new ConnectionDetector(getApplicationContext());
// get Internet status
isInternetPresent = cd.isConnectingToInternet();
ImageButton ntchecker= (ImageButton) findViewById(R.id.nt_check);
ntchecker.setOnClickListener(new OnClickListener()
@Override
public void onClick(View arg0)
// TODO Auto-generated method stub
Intent i = new Intent(AllProductsActivity.this,AllProductsActivity.class);
startActivity(i);
);
//jp pull to refresh
StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder() .detectAll().penaltyLog().build();
StrictMode.setThreadPolicy(policy);
listView = (PullToRefreshListView) getListView();
listView.setOnRefreshListener(new OnRefreshListener()
//@Override
public void onRefresh()
// Do work to refresh the list here.
productsList = new ArrayList<HashMap<String, String>>();
// Loading products in Background Thread
new LoadAllProducts().execute();
pDialog.hide();
);
// end of jp pull to refresh
// check for Internet status
if (isInternetPresent)
// Internet Connection is Present
// make HTTP requests
// Hashmap for ListView
productsList = new ArrayList<HashMap<String, String>>();
ntCheck.setVisibility(View.GONE); //hide internet checker
// Loading products in Background Thread
new LoadAllProducts().execute();
else
// Internet connection is not present
// Ask user to connect to Internet
Log.d("No Internet Connection", "You don't have internet connection.");
//Toast.makeText(this, "You don't have internet connection.", Toast.LENGTH_LONG).show();
ntCheck.setVisibility(View.VISIBLE);
btnNewProduct = (ImageButton) findViewById(R.id.newpost);
ImageButton searchBtn = (ImageButton) findViewById(R.id.SearchBtn);
btnNewProduct.setOnClickListener(new View.OnClickListener()
@Override
public void onClick(View view)
// Launching create new product activity
Intent i = new Intent(AllProductsActivity.this, NewProductActivity.class);
startActivity(i);
);
//end of jp
// Hashmap for ListView
//jpdast productsList = new ArrayList<HashMap<String, String>>();
// Loading products in Background Thread
//jpdast new LoadAllProducts().execute();
// Get listview
ListView lv = getListView();
// on seleting single product
// launching Edit Product Screen
lv.setOnItemClickListener(new OnItemClickListener()
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id)
// getting values from selected ListItem
String pid = ((TextView) view.findViewById(R.id.pid)).getText()
.toString();
// Starting new intent
Intent in = new Intent(getApplicationContext(),
ViewPro.class);
// sending pid to next activity
in.putExtra(TAG_PID, pid);
// starting new activity and expecting some response back
startActivityForResult(in, 100);
);
//jp scroller
//add the footer before adding the adapter, else the footer will not load!
// View footerView = ((LayoutInflater)this.getSystemService(Context.LAYOUT_INFLATER_SERVICE)).inflate(R.layout.footer, null, false);
// this.getListView().addFooterView(footerView);
//Here is where the magic happens
lv.setOnScrollListener(new OnScrollListener()
ListAdapter adapter = new SimpleAdapter(
AllProductsActivity.this, productsList,
R.layout.list_item, new String[] TAG_PID,
TAG_NAME,TAG_AUTH,TAG_HIT, TAG_DATE,
new int[] R.id.pid, R.id.name, R.id.auth, R.id.hit, R.id.date
);
@Override
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount)
int lastItem = firstVisibleItem + visibleItemCount;
int lastItemPosition=adapter.getCount();
if ( adapter.getCount() >= 10 && lastItem > adapter.getCount() - 6)
boolean isLoading = false;
if (!isLoading)
if(isInternetPresent)
if(lastItem > lastItemPosition)
//productsList = new ArrayList<HashMap<String, String>>();
// Loading products in Background Thread
new LoadAllProducts().execute();
//receivedData();
Log.d("LOG", "jpdesign is here");
((BaseAdapter) adapter).notifyDataSetChanged();
part += 1;
isLoading = true;
public void onScrollStateChanged(AbsListView view, int scrollState)
);
//jp end scroller
// Response from Edit Product Activity
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data)
super.onActivityResult(requestCode, resultCode, data);
// if result code 100
if (resultCode == 100)
// if result code 100 is received
// means user edited/deleted product
// reload this screen again
Intent intent = getIntent();
finish();
startActivity(intent);
/**
* Background Async Task to Load all product by making HTTP Request
* */
class LoadAllProducts extends AsyncTask<String, String, String>
/**
* Before starting background thread Show Progress Dialog
* */
@Override
protected void onPreExecute()
super.onPreExecute();
pDialog = new ProgressDialog(AllProductsActivity.this);
pDialog.setMessage("در حال دریافت اطلاعات ...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(false);
pDialog.show();
/**
* getting All products from url
* */
protected String doInBackground(String... args)
Log.d("LOG", part+"");
List<NameValuePair> params2 = new ArrayList<NameValuePair>();
params2.add(new BasicNameValuePair(TAG_JPPart, "" + part));
JSONObject json2 = jParser.makeHttpRequest(url_all_products, "POST", params2);
Log.d("post checker: ", json2.toString());
// Building Parameters
List<NameValuePair> params = new ArrayList<NameValuePair>();
// getting JSON string from URL
JSONObject json = jParser.makeHttpRequest(url_all_products, "GET", params);
// Check your log cat for JSON reponse
//Log.d("jpdesign All Products: ", json.toString());
try
// Checking for SUCCESS TAG
int success = json.getInt(TAG_SUCCESS);
if (success == 1 )
//adapter.notifyDataSetChanged();
refreshNumber="1";
// products found
// Getting Array of Products
products = json2.getJSONArray(TAG_PRODUCTS);
String myjpdate=json.getString(TAG_JPTIME);
// Log.d("TIME TEST", myjpdate);
Log.d("TIME TEST", products+"");
// looping through All Products
//for (int i = 0; i < products.length(); i++)
for (int i = 0; i < products.length(); i++)
JSONObject c = products.getJSONObject(i);
// Storing each json item in variable
String id = c.getString(TAG_PID);
String name = c.getString(TAG_NAME);
//jpcode
String auth = c.getString(TAG_AUTH);
String hit = c.getString(TAG_HIT);
String date = c.getString(TAG_DATE);
//jptime diff
String dateStart = date;
String dateStop = myjpdate;
Date d1 = null;
Date d2 = null;
Date jd1 = null;
Date jd2 = null;
Date fyear = null;
SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
SimpleDateFormat jpformat = new SimpleDateFormat("yyyy-MM-dd");
try
d1 = format.parse(dateStart);
d2 = format.parse(dateStop);
jd1 =jpformat.parse(dateStart);
jd2 =jpformat.parse(dateStop);
DateFormat formatter ;
formatter = new SimpleDateFormat("yyyy-MM-dd");
fyear = (Date)formatter.parse(dateStart);
// (3) create a new String using the date format we want
String YMD = formatter.format(fyear);
int len=YMD.length();
String[] myInArray=new String[len];
String FY=String.valueOf(YMD.charAt(0))+String.valueOf(YMD.charAt(1))+String.valueOf(YMD.charAt(2))+String.valueOf(YMD.charAt(3));
String FM=String.valueOf(YMD.charAt(5))+String.valueOf(YMD.charAt(6));
String FD=String.valueOf(YMD.charAt(8))+String.valueOf(YMD.charAt(9));
jCal.GregorianToPersian(Integer.parseInt(FY), Integer.parseInt(FM), Integer.parseInt(FD));
String myconverttime= jCal.toString();
//in milliseconds
long diff = d2.getTime() - d1.getTime();
long jpdiff = jd2.getTime() - jd1.getTime();
long diffSeconds = diff / 1000 % 60;
long diffMinutes = diff / (60 * 1000) % 60;
long diffHours = diff / (60 * 60 * 1000) % 24;
long diffDays = diff / (24 * 60 * 60 * 1000);
// 1s=1000 ,1m=60000,1h=3.6e+6 1day = 86400000
if(jpdiff==0 && diff<=60000) myjpdiff="هم اکنون";
if(jpdiff==0 && diff>60000 && diff<(59*60000)) myjpdiff=diffMinutes+" دقیقه قبل";
if(jpdiff==0 && diff>(60*60000) && diff<(24*59*60000)) myjpdiff=diffHours+" ساعت قبل";
if(jpdiff==86400000) myjpdiff=" 1 روز قبل ";
if(jpdiff>86400000) myjpdiff=myconverttime;
Log.d("TIME TEST",FY+" "+diff+" "+ jpdiff+" "+diffDays+"day "+diffHours+"hour "+diffMinutes+"");
catch (Exception e)
e.printStackTrace();
//end jptime diff
// creating new HashMap
HashMap<String, String> map = new HashMap<String, String>();
// adding each child node to HashMap key => value
map.put(TAG_PID, id);
map.put(TAG_NAME, name);
map.put(TAG_AUTH, auth); //jpcode
map.put(TAG_HIT, hit); //jpcode
map.put(TAG_DATE, myjpdiff); //jpcode
// adding HashList to ArrayList
productsList.add(map);
else
refreshNumber="0";
// no products found
// Launch Add New product Activity
Intent i = new Intent(getApplicationContext(),
NewProductActivity.class);
// Closing all previous activities
i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(i);
catch (JSONException e)
e.printStackTrace();
return null;
/**
* After completing background task Dismiss the progress dialog
* **/
protected void onPostExecute(String file_url)
// dismiss the dialog after getting all products
pDialog.dismiss();
// updating UI from Background Thread
runOnUiThread(new Runnable()
public void run()
/**
* Updating parsed JSON data into ListView
**/
// TextView dt=(TextView) findViewById(R.id.date);
// dt.setTypeface(jpfont);
ListAdapter adapter = new SimpleAdapter(
AllProductsActivity.this, productsList,
R.layout.list_item, new String[] TAG_PID,
TAG_NAME,TAG_AUTH,TAG_HIT, TAG_DATE,
new int[] R.id.pid, R.id.name, R.id.auth, R.id.hit, R.id.date
);
// updating listview
setListAdapter(adapter);
((PullToRefreshListView) getListView()).onRefreshComplete();
);
//jpcode logout
private void logoutUser()
session.setLogin(false);
db.deleteUsers();
// Launching the login activity
Intent intent = new Intent(AllProductsActivity.this, LoginActivity.class);
startActivity(intent);
finish();
//end jp logout
这是服务器上的 php 文件：
<?php
header("Cache-Control: no-cache, must-revalidate"); // HTTP/1.1
header("Expires: Sat, 26 Jul 2014 05:00:00 GMT"); // Date in the past
?>
<?php
/*
* Following code will list all the products
*/
// array for JSON response
$response = array();
// include db connect class
require_once __DIR__ . '/db_connect.php';
// connecting to db
$db = new DB_CONNECT();
// get all products from products table
//jpadd codes
$part = $_POST['part'];
//$part = $_GET['part'];
$start = $part * 10;
$result = mysql_query("SELECT *FROM products ORDER BY`created_at` DESC LIMIT $start, 10") or die(mysql_error());
//$result = mysql_query("SELECT *FROM products ORDER BY`created_at` DESC") or die(mysql_error());
// check for empty result
if (mysql_num_rows($result) > 0)
// looping through all results
// products node
$response["jptime"] = date("Y-m-d H:i:s");
//$jptime["my_date"]= date("Y-m-d H:i:s");
$response["products"] = array();
$response["part"] = $part;
while ($row = mysql_fetch_array($result))
// temp user array
$product = array();
$product["pid"] = $row["pid"];
$product["name"] = $row["name"];
//$product["price"] = $row["price"];
//$product["description"] = $row["description"];
$product["created_at"] = $row["created_at"];
//$product["updated_at"] = $row["updated_at"];
//jpcode
$product["auth"] = $row["auth"];
$product["hit"] = $row["hit"];
// $my_date = date("Y-m-d H:i:s");
// push single product into final response array
array_push($response["products"], $product);
// success
$response["success"] = 1;
// echoing JSON response
echo json_encode($response);
else
// no products found
$response["success"] = 0;
$response["message"] = "محصولی یافت نشد";
// echo no users JSON
echo json_encode($response);
?>
但是当用户向下滚动列表时没有任何反应
【问题讨论】：
首先从 Scroll 方法中删除适配器代码，然后尝试从 LoadAllProducts onPostExecute() 更新列表适配器。 签出：mobile.dzone.com/news/android-tutorial-dynamicaly 我删除了它，但发生了 nullexception 有什么解决办法吗？ 【参考方案1】：My application code which worked:
public class Product_Listing extends Fragment
private static final String TAG = SubCategoryActivity.class.getSimpleName();
private static final String TAG_IMAGEPATH = "imagepath";
private static final String TAG_PRODUCTID = "productid";
private static final String TAG_PRODUCTNAME = "productname";
private static final String TAG_SUPPLIERID = "supplierid";
private static final String TAG_SUPPLIERNAME = "suppliername";
private static final String TAG_CATEGORY_ID = "catid";
private static final String TAG_PRODUCT_COUNT = "productcount";
private ProgressDialog pDialog;
private List<Products> catList = new ArrayList<Products>();
private ListView listView;
private ProductsAdapter adapter;
int id_count = 0;
private int current_page = 0;
int mPreLast;
public Product_Listing()
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState)
return inflater.inflate(R.layout.fragment_product__listing, container, false);
@Override
public void onActivityCreated(@Nullable Bundle savedInstanceState)
super.onActivityCreated(savedInstanceState);
listView = (ListView) getView().findViewById(R.id.list1);
adapter = new ProductsAdapter(getActivity(), catList);
listView.setAdapter(adapter);
int currentPosition = listView.getFirstVisiblePosition();
listView.setSelectionFromTop(currentPosition + 1, 0);
listView.setOnScrollListener(new AbsListView.OnScrollListener()
@Override
public void onScrollStateChanged(AbsListView absListView, int i)
@Override
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount)
int lastItem = firstVisibleItem + visibleItemCount;
if(lastItem == totalItemCount)
if (mPreLast != lastItem)
mPreLast = lastItem;
new LoadProductDesc().execute();
);
new LoadProductDesc().execute();
private void hidePDialog()
if (pDialog != null && pDialog.isShowing())
pDialog.dismiss();
pDialog = null;
class LoadProductDesc extends AsyncTask<String, String, String>
/**
* Before starting background thread Show Progress Dialog
*/
@Override
protected void onPreExecute()
super.onPreExecute();
pDialog = new ProgressDialog(getActivity());
pDialog.setMessage("Getting Data ...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(true);
pDialog.show();
protected String doInBackground(String... args)
HttpClient httpclient = new DefaultHttpClient();
HttpResponse response;
String responseString = null;
try
// make a HTTP request
response = httpclient.execute(new HttpGet());
StatusLine statusLine = response.getStatusLine();
if (statusLine.getStatusCode() == HttpStatus.SC_OK)
ByteArrayOutputStream out = new ByteArrayOutputStream();
response.getEntity().writeTo(out);
out.close();
responseString = out.toString();
else
// close connection
response.getEntity().getContent().close();
throw new IOException(statusLine.getReasonPhrase());
catch (Exception e)
Log.d("Test", "Couldn't make a successful request!");
return responseString;
protected void onPostExecute(final String response)
super.onPostExecute(response);
// Creating volley request obj
String s1 = getActivity().getIntent().getStringExtra("index");
current_page += 1;
final String url = "Your URL Link" + s1 + "," + current_page;
JsonArrayRequest movieReq = new JsonArrayRequest(url,
new Response.Listener<JSONArray>()
@Override
public void onResponse(JSONArray response)
Log.d(TAG, response.toString());
try
if (isNetworkStatusAvialable (getActivity()))
// Parsing json
for (int i = 0; i < response.length() && response.length() != 0; i++)
JSONObject obj = response.getJSONObject(i);
Products products = new Products();
id_count = id_count + 1;
products.setProductName(obj.getString(TAG_PRODUCTNAME));
products.setThumbnailUrl(obj.getString(TAG_IMAGEPATH));
products.setProductID(obj.getInt(TAG_PRODUCTID));
products.setSupplierName(obj.getString(TAG_SUPPLIERNAME));
products.setSupplierID(obj.getInt(TAG_SUPPLIERID));
products.setCategoryID(obj.getInt(TAG_CATEGORY_ID));
String count = obj.getString(TAG_PRODUCT_COUNT);
catList.add(products);
TextView textView = (TextView) getView().findViewById(R.id.ListofProducts);
textView.setText(String.valueOf("Total 1 to " + id_count + " Products listed of " + count));
else
Toast.makeText(getActivity(),"Check Internet Connectivity!!",Toast.LENGTH_LONG).show();
return;
catch (JSONException e)
e.printStackTrace();
catch (NullPointerException ne)
Toast.makeText(getActivity(), "Check Internet Connectivity!!", Toast.LENGTH_LONG).show();
hidePDialog();
// notifying list adapter about data changes
// so that it renders the list view with updated data
adapter.notifyDataSetChanged();
, new Response.ErrorListener()
@Override
public void onErrorResponse(VolleyError error)
VolleyLog.d(TAG, "Error: " + error.getMessage());
hidePDialog();
);
// Adding request to request queue
AppController.getInstance().addToRequestQueue(movieReq);
public static boolean isNetworkStatusAvialable (Context context)
ConnectivityManager connectivityManager = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
if (connectivityManager != null)
NetworkInfo netInfos = connectivityManager.getActiveNetworkInfo();
if(netInfos != null)
if(netInfos.isConnected())
return true;
return false;
【讨论】：
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