在这个应用程序中，我创建了几个类别来从本地服务器带来新闻，它在类Art中我写了一个代码，允许从服务器中的URL加载图像，当我启动我的模拟器时选择Art，强行关闭
package com.example.mobilemagazine;
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.ImageView;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.TextView;
public class Art extends ListActivity {
// Progress Dialog
private ProgressDialog pDialog;
// Creating JSON Parser object
JSONParser jParser = new JSONParser();
ArrayList<HashMap<String, String>> newsList;
// url to get all products list
private static String url_all_news = "http://10.0.2.2/android_connect/news_art.php";
// JSON Node names
private static final String TAG_SUCCESS = "success";
private static final String TAG_NEWS = "news";
private static final String TAG_NEWID = "id";
private static final String TAG_TITLE = "title";
// products JSONArray
JSONArray News = null;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.news);
// Loader image - will be shown before loading image
int loader = R.drawable.ic_launcher;
// Imageview to show
ImageView image = (ImageView) findViewById(R.id.image);
// Image url
String image_url = "http://10.0.2.2/Images/1.jpg";
// ImageLoader class instance
ImageLoader imgLoader = new ImageLoader(getApplicationContext());
// whenever you want to load an image from url
// call DisplayImage function
// url - image url to load
// loader - loader image, will be displayed before getting image
// image - ImageView
imgLoader.DisplayImage(image_url, loader, image);
// Hashmap for ListView
newsList = new ArrayList<HashMap<String, String>>();
// Loading products in Background Thread
// 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 nid = ((TextView) view.findViewById(R.id.newid)).getText()
.toString();
// Starting new intent
Intent in = new Intent(getApplicationContext(),
Details.class);
// sending nid to next activity
in.putExtra(TAG_NEWID, nid);
// starting new activity and expecting some response back
startActivityForResult(in, 100);
}
});
new LoadAllProducts().execute();
}
//
@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);
}
}
class LoadAllProducts extends AsyncTask<String, String, String> {
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(Art.this);
pDialog.setMessage("Loading News. Please wait...");
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_news, "GET", params);
// Check your log cat for JSON reponse
Log.d("All News: ", json.toString());
try {
// Checking for SUCCESS TAG
int success = json.getInt(TAG_SUCCESS);
if (success == 1) {
// products found
// Getting Array of Products
News = json.getJSONArray(TAG_NEWS);
// looping through All Products
for (int i = 0; i < News.length(); i++) {
JSONObject c = News.getJSONObject(i);
// Storing each json item in variable
String id = c.getString(TAG_NEWID);
String title = c.getString(TAG_TITLE);
// creating new HashMap
HashMap<String, String> map = new HashMap<String, String>();
// adding each child node to HashMap key => value
map.put(TAG_NEWID, id);
map.put(TAG_TITLE, title);
// adding HashList to ArrayList
newsList.add(map);
}
}
else {
// no products found
// Launch Add New product Activity
Intent i = new Intent(getApplicationContext(), Empty.class);
// Closing all previous activities
i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(i);
}
} catch (JSONException e) {
e.printStackTrace();
}
return null;
}
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() {
ListAdapter adapter = new SimpleAdapter(
Art.this, newsList,
R.layout.tab_new, new String[] { TAG_NEWID, TAG_TITLE},
new int[] { R.id.newid, R.id.newtitle });
// updating listview
setListAdapter(adapter);
}
});
}}
}
LOG CAT：
10-26 20:30:37.738: E/AndroidRuntime(311): FATAL EXCEPTION: main
10-26 20:30:37.738: E/AndroidRuntime(311): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.mobilemagazine/com.example.mobilemagazine.TabList}: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.mobilemagazine/com.example.mobilemagazine.Art}: java.lang.NullPointerException
10-26 20:30:37.738: E/AndroidRuntime(311): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
10-26 20:30:37.738: E/AndroidRuntime(311): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
10-26 20:30:37.738: E/AndroidRuntime(311): at android.app.ActivityThread.access$2300(ActivityThread.java:125)
10-26 20:30:37.738: E/AndroidRuntime(311): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
10-26 20:30:37.738: E/AndroidRuntime(311): at android.os.Handler.dispatchMessage(Handler.java:99)
10-26 20:30:37.738: E/AndroidRuntime(311): at android.os.Looper.loop(Looper.java:123)
10-26 20:30:37.738: E/AndroidRuntime(311): at android.app.ActivityThread.main(ActivityThread.java:4627)
10-26 20:30:37.738: E/AndroidRuntime(311): at java.lang.reflect.Method.invokeNative(Native Method)
10-26 20:30:37.738: E/AndroidRuntime(311): at java.lang.reflect.Method.invoke(Method.java:521)
10-26 20:30:37.738: E/AndroidRuntime(311): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
10-26 20:30:37.738: E/AndroidRuntime(311): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
10-26 20:30:37.738: E/AndroidRuntime(311): at dalvik.system.NativeStart.main(Native Method)
10-26 20:30:37.738: E/AndroidRuntime(311): Caused by: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.mobilemagazine/com.example.mobilemagazine.Art}: java.lang.NullPointerException
10-26 20:30:37.738: E/AndroidRuntime(311): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
10-26 20:30:37.738: E/AndroidRuntime(311): at android.app.ActivityThread.startActivityNow(ActivityThread.java:2503)
10-26 20:30:37.738: E/AndroidRuntime(311): at android.app.LocalActivityManager.moveToState(LocalActivityManager.java:127)
10-26 20:30:37.738: E/AndroidRuntime(311): at android.app.LocalActivityManager.startActivity(LocalActivityManager.java:339)
10-26 20:30:37.738: E/AndroidRuntime(311): at android.widget.TabHost$IntentContentStrategy.getContentView(TabHost.java:651)
10-26 20:30:37.738: E/AndroidRuntime(311): at android.widget.TabHost.setCurrentTab(TabHost.java:323)
10-26 20:30:37.738: E/AndroidRuntime(311): at android.widget.TabHost.addTab(TabHost.java:213)
10-26 20:30:37.738: E/AndroidRuntime(311): at com.example.mobilemagazine.TabList.onCreate(TabList.java:68)
10-26 20:30:37.738: E/AndroidRuntime(311): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
10-26 20:30:37.738: E/AndroidRuntime(311): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
10-26 20:30:37.738: E/AndroidRuntime(311): ... 11 more
10-26 20:30:37.738: E/AndroidRuntime(311): Caused by: java.lang.NullPointerException
10-26 20:30:37.738: E/AndroidRuntime(311): at com.example.mobilemagazine.ImageLoader.DisplayImage(ImageLoader.java:46)
10-26 20:30:37.738: E/AndroidRuntime(311): at com.example.mobilemagazine.Art.onCreate(Art.java:78)
10-26 20:30:37.738: E/AndroidRuntime(311): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
10-26 20:30:37.738: E/AndroidRuntime(311): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
10-26 20:30:37.738: E/AndroidRuntime(311): ... 20 more