我试图解析列表视图中的一些项目，当我向下滚动时，我想获取更多产品并将它们添加到列表中。但是我的代码没有这样做，它要么刷新它，要么崩溃。有什么帮助吗？添加页脚也不起作用，我得到一个classcastexception
JSON解析器：
package com.lars.json;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import com.lars.R.drawable;
import android.R;
import android.util.Log;
/** A class to parse json data */
public class JSONParser {
// Receives a JSONObject and returns a list
public List<HashMap<String,Object>> parse(JSONObject jObject){
JSONArray jProducts = null;
try {
// Retrieves all the elements in the 'countries' array
jProducts = jObject.getJSONArray("products");
} catch (JSONException e) {
e.printStackTrace();
}
// Invoking getCountries with the array of json object
// where each json object represent a country
return getProducts(jProducts);
}
private List<HashMap<String, Object>> getProducts(JSONArray jProducts){
int productsCount = jProducts.length();
List<HashMap<String, Object>> productList = new ArrayList<HashMap<String,Object>>();
HashMap<String, Object> product = null;
// Taking each country, parses and adds to list object
for(int i=0; i<productsCount;i++){
try {
// Call getCountry with country JSON object to parse the country
product = getJSON((JSONObject)jProducts.get(i));
productList.add(product);
} catch (JSONException e) {
e.printStackTrace();
}
}
return productList;
}
// Parsing the Country JSON object
private HashMap<String, Object> getJSON(JSONObject f){
HashMap<String, Object> country = new HashMap<String, Object>();
String id = "";
String naam = "";
String status = "";
String prijs = "";
String productnum = "";
try {
String priceone = f.getString("prijsex");
id = f.getString("id");
naam = f.getString("naam");
status = f.getString("status");
prijs = "€" + priceone;
productnum = f.getString("productnum");
country.put("id", id);
country.put("naam", naam);
country.put("img", com.lars.R.drawable.tlogotrans);
country.put("prijs", prijs);
country.put("img_path", "http://www.lars.com/images/" + productnum + ".jpg");
if(Integer.parseInt(status) > 0){
country.put("status", com.lars.R.drawable.stock);
}else{
country.put("status", com.lars.R.drawable.nostock);
}
} catch (JSONException e) {
e.printStackTrace();
}
return country;
}
}
下载任务和 Listview 加载器：
/** A method to download json data from url */
private String downloadUrl(String strUrl) throws IOException{
String data = "";
InputStream iStream = null;
try{
URL url = new URL(strUrl);
// Creating an http connection to communicate with url
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
// Connecting to url
urlConnection.connect();
// Reading data from url
iStream = urlConnection.getInputStream();
BufferedReader br = new BufferedReader(new InputStreamReader(iStream));
StringBuffer sb = new StringBuffer();
String line = "";
while( ( line = br.readLine()) != null){
sb.append(line);
}
data = sb.toString();
br.close();
}catch(Exception e){
Log.d("Exception while downloading url", e.toString());
}finally{
iStream.close();
}
return data;
}
/** AsyncTask to download json data */
private class DownloadTask extends AsyncTask<String, Integer, String>{
String data = null;
@Override
protected String doInBackground(String... url) {
try{
data = downloadUrl(url[0]);
}catch(Exception e){
Log.d("Background Task",e.toString());
}
return data;
}
@Override
protected void onPostExecute(String result) {
// The parsing of the xml data is done in a non-ui thread
ListViewLoaderTask listViewLoaderTask = new ListViewLoaderTask();
Log.i("Result", result);
if(result.equals(" ")){
Log.i("No img", "No Img");
}else{
listViewLoaderTask.execute(result);
}
// Start parsing xml data
}
}
/** AsyncTask to parse json data and load ListView */
private class ListViewLoaderTask extends AsyncTask<String, Void, SimpleAdapter>{
JSONObject jObject;
private List<HashMap<String, Object>> products;
// Doing the parsing of xml data in a non-ui thread
@Override
protected SimpleAdapter doInBackground(String... strJson) {
try{
jObject = new JSONObject(strJson[0]);
JSONParser jsonpars = new JSONParser();
jsonpars.parse(jObject);
}catch(Exception e){
Log.d("JSON Exception1",e.toString());
}
// Instantiating json parser class
JSONParser jsonpars = new JSONParser();
// A list object to store the parsed countries list
try{
// Getting the parsed data as a List construct
if(set == 0){
products = jsonpars.parse(jObject);
}else{
products.addAll(jsonpars.parse(jObject));
}
}catch(Exception e){
Log.d("Exception",e.toString());
}
// Keys used in Hashmap
String[] from = { "img","naam","status","prijs"};
// Ids of views in listview_layout
int[] to = { R.id.imPThumb,R.id.tvPRName,R.id.imstock,R.id.tvPRPrijs};
// Instantiating an adapter to store each items
// R.layout.listview_layout defines the layout of each item
SimpleAdapter adapter = new SimpleAdapter(getBaseContext(), products, R.layout.productlijstrow, from, to);
return adapter;
}
@Override
protected void onProgressUpdate(Void... values) {
// TODO Auto-generated method stub
publishProgress();
Log.i("ListView Loader Task", "Update");
super.onProgressUpdate(values);
}
/** Invoked by the Android on "doInBackground" is executed */
@SuppressWarnings("unchecked")
@Override
protected void onPostExecute(SimpleAdapter adapter) {
// View v = getLayoutInflater().inflate(R.layout.footerview, null);
//list.addFooterView(v);
// Setting adapter for the listview
list.setAdapter(adapter);
if(set == 0){
list.setOnScrollListener(onAnswersScrolled);
set++;
}
list.setOnItemClickListener(onAnswerClicked);
list.setTextFilterEnabled(true);
/* list.setOnItemClickListener(new OnItemClickListener() {
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
@SuppressWarnings("unchecked")
HashMap<String, String> o = (HashMap<String, String>) lv.getItemAtPosition(position);
Bundle extra = new Bundle();
Intent i = new Intent("com.lars.productdescription");
extra.putString("id", o.get("id"));
i.putExtras(extra);
startActivity(i);
}
});*/
for(int i=0;i<adapter.getCount();i++){
HashMap<String, Object> hm = (HashMap<String, Object>) adapter.getItem(i);
String imgUrl = (String) hm.get("img_path");
Log.i("imgurlonPost", imgUrl);
ImageLoaderTask imageLoaderTask = new ImageLoaderTask();
HashMap<String, Object> hmDownload = new HashMap<String, Object>();
hmDownload.put("img_path",imgUrl);
hmDownload.put("position", i);
// Starting ImageLoaderTask to download and populate image in the listview
imageLoaderTask.execute(hmDownload);
adapter.notifyDataSetChanged();
}
/* list.setOnScrollListener(new OnScrollListener(){
});*/
}
}
/** AsyncTask to download and load an image in ListView */
private class ImageLoaderTask extends AsyncTask<HashMap<String, Object>, Void, HashMap<String, Object>>{
@Override
protected HashMap<String, Object> doInBackground(HashMap<String, Object>... hm) {
InputStream iStream=null;
String imgUrl = (String) hm[0].get("img_path");
int position = (Integer) hm[0].get("position");
HashMap<String, Object> hmBitmap = new HashMap<String, Object>();
URL url;
try {
url = new URL(imgUrl);
// Creating an http connection to communicate with url
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
Log.i("imgUrl", imgUrl);
// Connecting to url
urlConnection.connect();
// Log.i("Response", urlConnection.getResponseMessage());
// Reading data from url
if(urlConnection.getResponseMessage().contains("OK")){
iStream = urlConnection.getInputStream();
// Getting Caching directory
File cacheDirectory = getBaseContext().getCacheDir();
cacheDirectory.delete();
// Temporary file to store the downloaded image
File tmpFile = new File(cacheDirectory.getPath() + "/wpta_"+position+".png");
// The FileOutputStream to the temporary file
FileOutputStream fOutStream = new FileOutputStream(tmpFile);
// Creating a bitmap from the downloaded inputstream
Bitmap b = BitmapFactory.decodeStream(iStream);
// Writing the bitmap to the temporary file as png file
b.compress(Bitmap.CompressFormat.PNG,100, fOutStream);
// Flush the FileOutputStream
fOutStream.flush();
//Close the FileOutputStream
fOutStream.close();
// Create a hashmap object to store image path and its position in the listview
// Storing the path to the temporary image file
hmBitmap.put("img",tmpFile.getPath());
// Storing the position of the image in the listview
hmBitmap.put("position",position);
// Returning the HashMap object containing the image path and position
return hmBitmap;
}else{
Log.i("nope", "nb");
String uriStr = "android.resource://" + "com.lars" + "/" + R.drawable.ic_launcher;
hmBitmap.put("img", uriStr);
hmBitmap.put("position",position);
return hmBitmap;
}
}catch (Exception e) {
e.printStackTrace();
}
return null;
}
@SuppressWarnings("unchecked")
@Override
protected void onPostExecute(HashMap<String, Object> result) {
// Getting the path to the downloaded image
String path = (String) result.get("img");
// Getting the position of the downloaded image
int position = (Integer) result.get("position");
// Getting adapter of the listview
adapter = (SimpleAdapter ) list.getAdapter();
// Getting the hashmap object at the specified position of the listview
HashMap<String, Object> hm = (HashMap<String, Object>) adapter.getItem(position);
// Overwriting the existing path in the adapter
hm.put("img",path);
// Noticing listview about the dataset changes
adapter.notifyDataSetChanged();
}
@Override
protected void onProgressUpdate(Void... values) {
// TODO Auto-generated method stub
publishProgress();
adapter.notifyDataSetChanged();
Log.i("Image Task", "Update");
super.onProgressUpdate(values);
}
}
private OnItemClickListener onAnswerClicked = new OnItemClickListener() {
public void onItemClick(AdapterView<?> parent, View view, int position,
long id) {
@SuppressWarnings("unchecked")
HashMap<String, String> o = (HashMap<String, String>) parent.getItemAtPosition(position);
Bundle extra = new Bundle();
Intent i = new Intent("com.lars.productdescription");
extra.putString("id", o.get("id"));
i.putExtras(extra);
startActivity(i);
}
};
private OnScrollListener onAnswersScrolled = new OnScrollListener() {
public void onScroll(AbsListView view, int first, int visibleitems, int totalitemcount) {
// TODO Auto-generated method stub
int lastInScreen = first + visibleitems;
if(lastInScreen == totalitemcount){
if(kf == 0){
Log.i("onScroll", "" + c);
Log.i("kf", "0");
String filfinal = keuze.replace(" ", "thisisaspace");
String strUrl = "http://www.lars.nl/getName.php?name=" + filfinal + "&page=" + c ;
DownloadTask downloadTask = new DownloadTask();
downloadTask.execute(strUrl);
c = c + o;
Log.i("After Scroll", "" + c);
}else{
Log.i("onScroll", "" + c);
Log.i("kf", "1");
String strUrl = "http://www.lars.nl/get.php?id=" + filter + "&page=" + c ;
DownloadTask downloadTask = new DownloadTask();
downloadTask.execute(strUrl);
c = c + o;
Log.i("After Scroll", "" + c);
}
}
}
public void onScrollStateChanged(AbsListView view, int scrollstate) {
// TODO Auto-generated method stub
}
};
}