我正在尝试从 mysql 数据库中获取数据并将其加载到 ListView 中，但无法执行此操作，因为在出现进度对话框后应用程序崩溃了。logcat 显示错误为执行 doInBackground() 时发生错误。请帮忙我，这是我的java文件
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import org.apache.http.NameValuePair;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.app.ListActivity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;
public class CompScience extends ListActivity{
// 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://10.0.2.2/books/get_all_books.php";
// JSON Node names
private static final String TAG_SUCCESS = "success";
private static final String TAG_PRODUCTS = "computerscience";
private static final String TAG_PID = "bid";
private static final String TAG_NAME = "title";
private static final String TAG_DESCRIPTION = "author";
// products JSONArray
JSONArray computerscience = null;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_comp_science);
// Hashmap for ListView
productsList = new ArrayList<HashMap<String, String>>();
// Loading products in Background Thread
new LoadAllProducts().execute();
// Get listview
ListView lv = getListView();
// on seleting single product
// launching Product Screen
lv.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
//String description = ((TextView) view).getText().toString();
Intent i = new Intent(CompScience.this,List1.class);
// i.putExtra("description", description);
startActivity(i);
}
});
}
class LoadAllProducts extends AsyncTask<String, String, String> {
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(CompScience.this);
pDialog.setMessage("Loading...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(false);
pDialog.show();
}
protected String doInBackground(String... args) {
// 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("All Products: ", json.toString());
try {
// Checking for SUCCESS TAG
int success = json.getInt(TAG_SUCCESS);
if (success == 1) {
// products found
// Getting Array of Products
computerscience = json.getJSONArray(TAG_PRODUCTS);
// looping through All Products
for (int i = 0; i < computerscience.length(); i++) {
JSONObject c = computerscience.getJSONObject(i);
// Storing each json item in variable
String id = c.getString(TAG_PID);
String name = c.getString(TAG_NAME);
String description = c.getString(TAG_DESCRIPTION);
// 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_DESCRIPTION, description);
// adding HashList to ArrayList
productsList.add(map);
}
} else {
Log.e(TAG_PRODUCTS, "No products found");
}
} 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
* */
ListAdapter adapter = new SimpleAdapter(
CompScience.this, productsList,
R.layout.list_item, new String[] { TAG_PID,
TAG_NAME,TAG_DESCRIPTION},
new int[] { R.id.bid, R.id.title,R.id.author });
// updating listview
setListAdapter(adapter);
}
});
}
}
这是日志
04-08 02:59:40.928: E/AndroidRuntime(2224): FATAL EXCEPTION: AsyncTask #1
04-08 02:59:40.928: E/AndroidRuntime(2224): java.lang.RuntimeException: An error occured while executing doInBackground()
04-08 02:59:40.928: E/AndroidRuntime(2224): at android.os.AsyncTask$3.done(AsyncTask.java:299)
04-08 02:59:40.928: E/AndroidRuntime(2224): at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:352)
04-08 02:59:40.928: E/AndroidRuntime(2224): at java.util.concurrent.FutureTask.setException(FutureTask.java:219)
04-08 02:59:40.928: E/AndroidRuntime(2224): at java.util.concurrent.FutureTask.run(FutureTask.java:239)
04-08 02:59:40.928: E/AndroidRuntime(2224): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
04-08 02:59:40.928: E/AndroidRuntime(2224): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
04-08 02:59:40.928: E/AndroidRuntime(2224): at java.lang.Thread.run(Thread.java:841)
04-08 02:59:40.928: E/AndroidRuntime(2224): Caused by: java.lang.NullPointerException
04-08 02:59:40.928: E/AndroidRuntime(2224): at com.example.dashboard.CompScience$LoadAllProducts.doInBackground(CompScience.java:94)
04-08 02:59:40.928: E/AndroidRuntime(2224): at com.example.dashboard.CompScience$LoadAllProducts.doInBackground(CompScience.java:1)
04-08 02:59:40.928: E/AndroidRuntime(2224): at android.os.AsyncTask$2.call(AsyncTask.java:287)
04-08 02:59:40.928: E/AndroidRuntime(2224): at java.util.concurrent.FutureTask.run(FutureTask.java:234)
04-08 02:59:40.928: E/AndroidRuntime(2224): ... 3 more
浏览器响应:
{
"computerscience": [
{
"bid": "1",
"title": "Electronic Principles",
"author": "Albert Malvino & David J Bates"
},
{
"bid": "2",
"title": "Electronic Circuits",
"author": "RD Sudhakar"
},
{
"bid": "3",
"title": "Digital Principles & Applications",
"author": "Leach, Malvino, Saha"
}
],
"success": 1
}
最佳答案
试试看:
List<NameValuePair> params = new ArrayList<NameValuePair>();
// getting JSON string from URL
params.add(new BasicNameValuePair(TAG_APPID, appID));
JSONObject json = jParser.makeHttpRequest(url_all_products, "GET",
params);
// Check your log cat for JSON reponse
Log.d("All Products: ", json.toString());
有你需要的参数:
params.add(new BasicNameValuePair(TAG_APPID, appID));
关于java - 致命异常 :Async Task #1，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/22930456/