您好我想从我的服务器下载一个json文件并将此json添加到列表视图我使用asyncktask方法和列表适配器处理片段 但是我得到了这个错误
10-27 14:45:30.385: E/AndroidRuntime(2074): FATAL EXCEPTION: main
10-27 14:45:30.385: E/AndroidRuntime(2074): java.lang.NullPointerException
10-27 14:45:30.385: E/AndroidRuntime(2074): at com.mihanServer.Fragments.NewsFragment$JsonReader.onPostExecute(NewsFragment.java:89)
10-27 14:45:30.385: E/AndroidRuntime(2074): at com.mihanServer.Fragments.NewsFragment$JsonReader.onPostExecute(NewsFragment.java:1)
10-27 14:45:30.385: E/AndroidRuntime(2074): at android.os.AsyncTask.finish(AsyncTask.java:631)
10-27 14:45:30.385: E/AndroidRuntime(2074): at android.os.AsyncTask.access$600(AsyncTask.java:177)
10-27 14:45:30.385: E/AndroidRuntime(2074): at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644)
10-27 14:45:30.385: E/AndroidRuntime(2074): at android.os.Handler.dispatchMessage(Handler.java:99)
10-27 14:45:30.385: E/AndroidRuntime(2074): at android.os.Looper.loop(Looper.java:137)
10-27 14:45:30.385: E/AndroidRuntime(2074): at android.app.ActivityThread.main(ActivityThread.java:5041)
10-27 14:45:30.385: E/AndroidRuntime(2074): at java.lang.reflect.Method.invokeNative(Native Method)
10-27 14:45:30.385: E/AndroidRuntime(2074): at java.lang.reflect.Method.invoke(Method.java:511)
10-27 14:45:30.385: E/AndroidRuntime(2074): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
10-27 14:45:30.385: E/AndroidRuntime(2074): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
10-27 14:45:30.385: E/AndroidRuntime(2074): at dalvik.system.NativeStart.main(Native Method)
这是我的片段代码
import java.util.ArrayList;
import java.util.List;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import com.mihanServer.sedasema.CustomListAdapter;
import com.mihanServer.sedasema.JSONParser;
import com.mihanServer.sedasema.MainActivity;
import com.mihanServer.sedasema.News;
import com.mihanServer.sedasema.R;
import android.app.ProgressDialog;
import android.database.DataSetObservable;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.webkit.WebView.FindListener;
import android.widget.ListView;
public class NewsFragment extends Fragment {
private static final String url = "http://192.168.1.6/web/app_dev.php/news/list";
private List<News> newsList = new ArrayList<News>();
private ListView listView;
private CustomListAdapter adapter;
private JSONArray jArray;
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.news , container, false);
listView = (ListView)rootView.findViewById(R.id.list);
try
{
adapter = new CustomListAdapter(getActivity(),newsList);
listView.setAdapter(adapter);
}
catch(Exception ex)
{
ex.printStackTrace();
}
new JsonReader().execute();
return rootView;
}
public class JsonReader extends AsyncTask<String, String, JSONObject>{
private ProgressDialog pDialog;
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(getActivity());
pDialog.setMessage("Getting Data ...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(true);
pDialog.show();
}
@Override
protected JSONObject doInBackground(String... args) {
JSONParser jParser = new JSONParser();
JSONObject json = jParser.getJSONFromUrl(url);
return json;
}
@Override
protected void onPostExecute(JSONObject json) {
pDialog.dismiss();
try {
// Getting JSON Array
jArray = json.getJSONArray("news");
for (int i = 0; i < jArray.length(); i++) {
try {
News news = new News();
JSONObject obj = jArray.getJSONObject(i);
news.setNewsTitle(obj.getString("title"));
news.setNewsThumbnailUrl(obj.getString("thumbnail"));
news.setNewsReleaseTime( obj.getString("created"));
news.setNewsBody(obj.getString("body"));
news.setNewsId(obj.getInt("id"));
// adding app to app array
newsList.add(news);
}
catch (JSONException e) {
e.printStackTrace();
}
adapter.notifyDataSetChanged();
}
}
catch (JSONException ex){
ex.printStackTrace();
}
}
}
}
在行通知数据集更改后，我收到错误。
这是我的列表适配器代码
import com.mihanServer.sedasema.R;
import java.util.List;
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.view.LayoutInflater;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.TextView;
import com.android.volley.toolbox.ImageLoader;
import com.android.volley.toolbox.NetworkImageView;
import com.mihanServer.sedasema.MainActivity;
import com.mihanServer.sedasema.AppController;
import com.mihanServer.sedasema.News;
public class CustomListAdapter extends BaseAdapter {
private final Activity actitity;
private LayoutInflater inflater;
private List<News> newsItems;
ImageLoader imageLoader = AppController.getInstance().getImageLoader();
News news;
public CustomListAdapter(Activity activity,List<News> newsItems) {
this.newsItems = newsItems;
this.actitity =activity;
imageLoader = new AppController().getImageLoader();
}
@Override
public int getCount() {
return newsItems.size();
}
@Override
public Object getItem(int location) {
return newsItems.get(location);
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(final int position, View convertView, ViewGroup parent) {
final Context context = parent.getContext();
inflater = (LayoutInflater)context.getSystemService
(Context.LAYOUT_INFLATER_SERVICE);
//inflater = (LayoutInflater) activity
// .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
if (convertView == null)
convertView = inflater.inflate(R.layout.news_list, null);
//comment for image reading
if (imageLoader == null)
imageLoader = AppController.getInstance().getImageLoader();
NetworkImageView newsthumbnail = (NetworkImageView) convertView
.findViewById(R.id.news_image);
TextView newsTitle = (TextView) convertView.findViewById(R.id.news_title);
//TextView newsBody = (TextView) convertView.findViewById(R.id.news_body);
TextView newsReleaseTime = (TextView) convertView.findViewById(R.id.news_release_time);
// getting news data for the row
news = newsItems.get(position);
//comment for image reading
newsthumbnail.setImageUrl(news.getNewsThumbnailUrl(), imageLoader);
newsTitle.setText(news.getNewsTitle());
newsReleaseTime.setText( news.getNewsReleaseTime());
//newsBody.setText(news.getNewsBody());
convertView.setOnClickListener(new OnClickListener() {
//@Override
public void onClick(View arg0) {
news=newsItems.get(position);
Intent intent = new Intent(actitity.getApplicationContext(),NewsDetails.class).setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
intent.putExtra("title",news.getNewsTitle());
intent.putExtra("body", news.getNewsBody());
intent.putExtra("newsimage", news.getNewsThumbnailUrl());
intent.putExtra("releasedtime", news.getNewsReleaseTime());
actitity.getApplicationContext().startActivity(intent);
}
});
return convertView;
}
}
这是我的json解析器
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.net.Socket;
import java.net.URL;
import java.net.UnknownHostException;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONException;
import org.json.JSONObject;
import android.util.Log;
public class JSONParser {
static InputStream is = null;
static JSONObject jObj = null;
static String json = "";
static Socket socket = null;
public JSONParser() {
}
public JSONObject getJSONFromUrl(String url) {
try{
//try {
//URL urlS = new URL(url);
try {
// defaultHttpClient
DefaultHttpClient httpClient = new DefaultHttpClient();
HttpGet httpGet = new HttpGet(url);
HttpResponse httpResponse = httpClient.execute(httpGet);
HttpEntity httpEntity = httpResponse.getEntity();
is = httpEntity.getContent();
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
/*catch (UnknownHostException e) {
e.printStackTrace();
json = "UnknownHostException: " + e.toString();
}*/
//is = urlS.openStream();
//}
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(
is, "iso-8859-1"), 8);
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = reader.readLine()) != null) {
sb.append(line + "");
}
is.close();
json = sb.toString();
//json = json.replace(""", "\"");
} catch (Exception e) {
Log.e("Buffer Error", "Error converting result " + e.toString());
}
// try parse the string to a JSON object
try {
jObj = new JSONObject(json);
} catch (JSONException e) {
Log.e("JSON Parser", "Error parsing data " + e.toString());
}
// return JSON String
}/*catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
json = "IOException: " + e.toString();*/
// }
finally{
if(socket != null){
try {
socket.close();
}
catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
return jObj;
}
}
我也使用volley lib来下载这样的图像
http://www.androidhive.info/2014/07/android-custom-listview-with-image-and-text-using-volley/
答案 0 :(得分：0)
尝试使用适配器类中的以下更改：
public class CustomListAdapter extends BaseAdapter {
private final Activity actitity;
private LayoutInflater inflater;
private List<News> newsItems;
private AQuery aQuery;
//ImageLoader imageLoader = AppController.getInstance().getImageLoader();
News news;
public CustomListAdapter(Activity activity,List<News> newsItems) {
this.newsItems = newsItems;
this.actitity =activity;
aQuery=new AQuery(activity);
// imageLoader = new AppController().getImageLoader();
}
@Override
public int getCount() {
return newsItems.size();
}
@Override
public Object getItem(int location) {
return newsItems.get(location);
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(final int position, View convertView, ViewGroup parent) {
final Context context = parent.getContext();
inflater = (LayoutInflater)context.getSystemService
(Context.LAYOUT_INFLATER_SERVICE);
//inflater = (LayoutInflater) activity
// .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
if (convertView == null)
convertView = inflater.inflate(R.layout.news_list, null);
//comment for image reading
/*if (imageLoader == null)
imageLoader = AppController.getInstance().getImageLoader();*/
NetworkImageView newsthumbnail = (NetworkImageView) convertView
.findViewById(R.id.news_image);
TextView newsTitle = (TextView) convertView.findViewById(R.id.news_title);
//TextView newsBody = (TextView) convertView.findViewById(R.id.news_body);
TextView newsReleaseTime = (TextView) convertView.findViewById(R.id.news_release_time);
// getting news data for the row
news = newsItems.get(position);
if(news.getNewsThumbnailUrl().length()>0){
aQuery.id(newsthumbnail).image(news.getNewsThumbnailUrl(),true,true);
}else{
newsthumbnail.setVisibility(View.GONE);
}
//comment for image reading
//newsthumbnail.setImageUrl(news.getNewsThumbnailUrl(), imageLoader);
newsTitle.setText(news.getNewsTitle());
newsReleaseTime.setText( news.getNewsReleaseTime());
//newsBody.setText(news.getNewsBody());
convertView.setOnClickListener(new OnClickListener() {
//@Override
public void onClick(View arg0) {
news=newsItems.get(position);
Intent intent = new Intent(actitity.getApplicationContext(),NewsDetails.class).setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
intent.putExtra("title",news.getNewsTitle());
intent.putExtra("body", news.getNewsBody());
intent.putExtra("newsimage", news.getNewsThumbnailUrl());
intent.putExtra("releasedtime", news.getNewsReleaseTime());
actitity.getApplicationContext().startActivity(intent);
}
});
return convertView;
}
}