我正在尝试实现从服务器（JSON）格式获取数据的代码，然后将其发送到Sqlite数据库，并从Sqlite发送到列表视图。但是我得到了一个nullpointer exeption。任何帮助表示赞赏：）
从GCMBroadcastReceiver调用该活动。可能是问题所在，因为代码本身可以工作，但是当它从广播接收器调用时却不能。
ReceiveActivity。
package com.techlovejump.gcm;
import java.util.ArrayList;
import java.util.List;
import org.apache.http.NameValuePair;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import com.techlovejump.user.GCM.ContactListAdapter;
import com.techlovejump.user.GCM.ContactListItems;
import com.techlovejump.user.GCM.SqlDbHelper;
import com.techlovejump.user.GCM.SqlHandler;
import android.os.AsyncTask;
import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.database.Cursor;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.TextView;
public class ReceiveActivity extends Activity {
SqlHandler sqlHandler;
ListView lvCustomList;
EditText IconBearing, BusName, DistanceInfo;
Button btnsubmit;
JSONParser jsonParser = new JSONParser();
JSONArray products = null;
private static String URL_Distance = "http://10.0.2.2/GET_EVERYTHING_TOGTHER/Get_Distance_From_Database.php";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
sqlHandler = new SqlHandler(this);
new Get_Distance_Data().execute();
showList();
}
private void showList() {
ArrayList<ContactListItems> contactList = new ArrayList<ContactListItems>();
contactList.clear();
String query = "SELECT * FROM GPS_INFORMATION ";
Cursor c1 = sqlHandler.selectQuery(query);
if (c1 != null && c1.getCount() != 0) {
if (c1.moveToFirst()) {
do {
ContactListItems contactListItems = new ContactListItems();
contactListItems.setIcon_Bearing(c1.getString(c1
.getColumnIndex("Bus_Name")));
contactListItems.setBus_Name(c1.getString(c1
.getColumnIndex("Distance_Info")));
contactListItems.setDistance_Info(c1.getString(c1
.getColumnIndex("Icon_Bearing")));
contactList.add(contactListItems);
} while (c1.moveToNext());
}
}
c1.close();
ContactListAdapter contactListAdapter = new ContactListAdapter(
ReceiveActivity.this, contactList);
lvCustomList.setAdapter(contactListAdapter);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
// getMenuInflater().inflate(R.menu.receive, menu);
return true;
}
class Get_Distance_Data extends AsyncTask<String, String, String> {
/**
* Before starting background thread Show Progress Dialog
* */
@Override
protected void onPreExecute() {
super.onPreExecute();
}
/**
* Creating product
* */
protected String doInBackground(String... args) {
// Building Parameters
List<NameValuePair> params = new ArrayList<NameValuePair>();
// getting JSON string from URL
JSONObject json = jsonParser.makeHttpRequest(URL_Distance, "GET",
params);
// Check your log cat for JSON reponse
Log.d("All Products: ", json.toString());
try {
// Checking for SUCCESS TAG
int success = json.getInt("success");
if (success == 1) {
// products found
// Getting Array of Products
products = json.getJSONArray("products");
// looping through All Products
for (int i = 0; i < products.length(); i++) {
JSONObject c = products.getJSONObject(i);
// Storing each json item in variable
String Distance = c.getString("Distance");
String Image = "none";
String BusName = "Bus1";
Log.i("Distance", Distance);
try {
String query = "INSERT INTO GPS_INFORMATION(Bus_Name,Distance_Info,Icon_Bearing) values ('"
+ Image + "','" + BusName +"','" + Distance +"')";
sqlHandler.executeQuery(query);
} catch (Exception e) {
Log.i("error","this is where the error happens");
}
}
}
} catch (JSONException e) {
e.printStackTrace();
}
return null;
}
/**
* After completing background task Dismiss the progress dialog
* **/
protected void onPostExecute(String file_url) {
// dismiss the dialog once done
}
}
}
这是SqlHandler类
package com.techlovejump.user.GCM;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
public class SqlHandler {
public static final String DATABASE_NAME = "DataBaseLocal";
public static final int DATABASE_VERSION = 1;
Context context;
SQLiteDatabase sqlDatabase;
SqlDbHelper dbHelper;
public SqlHandler(Context context) {
dbHelper = new SqlDbHelper(context, DATABASE_NAME, null,
DATABASE_VERSION);
sqlDatabase = dbHelper.getWritableDatabase();
}
public void executeQuery(String query) {
try {
if (sqlDatabase.isOpen()) {
sqlDatabase.close();
}
sqlDatabase = dbHelper.getWritableDatabase();
sqlDatabase.execSQL(query);
} catch (Exception e) {
System.out.println("DATABASE ERROR " + e);
}
}
public Cursor selectQuery(String query) {
Cursor c1 = null;
try {
if (sqlDatabase.isOpen()) {
sqlDatabase.close();
}
sqlDatabase = dbHelper.getWritableDatabase();
c1 = sqlDatabase.rawQuery(query, null);
} catch (Exception e) {
System.out.println("DATABASE ERROR " + e);
}
return c1;
}
}
这是logCat
12-30 09:26:03.369: I/GCM Demo(2111): Working... 1/5 @ 25458954
12-30 09:26:03.898: I/GCM Demo(2111): Working... 2/5 @ 25459479
12-30 09:26:04.465: I/GCM Demo(2111): Working... 3/5 @ 25460046
12-30 09:26:05.036: I/GCM Demo(2111): Working... 4/5 @ 25460618
12-30 09:26:05.549: I/GCM Demo(2111): Working... 5/5 @ 25461132
12-30 09:26:06.059: I/GCM Demo(2111): Completed work @ 25461640
12-30 09:26:06.059: I/MSG(2111): New Distance data
12-30 09:26:06.059: E/msg(2111): New Distance data
12-30 09:26:06.059: I/GCM Demo(2111): Received: Bundle[{message=New Distance data, android.support.content.wakelockid=1, collapse_key=do_not_collapse, from=616159599278}]
12-30 09:26:06.149: I/this(2111): it is working
12-30 09:26:06.999: D/AndroidRuntime(2111): Shutting down VM
12-30 09:26:06.999: W/dalvikvm(2111): threadid=1: thread exiting with uncaught exception (group=0x41465700)
12-30 09:26:07.119: E/AndroidRuntime(2111): FATAL EXCEPTION: main
12-30 09:26:07.119: E/AndroidRuntime(2111): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.techlovejump.gcm/com.techlovejump.gcm.ReceiveActivity}: java.lang.NullPointerException
12-30 09:26:07.119: E/AndroidRuntime(2111): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
12-30 09:26:07.119: E/AndroidRuntime(2111): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
12-30 09:26:07.119: E/AndroidRuntime(2111): at android.app.ActivityThread.access$600(ActivityThread.java:141)
12-30 09:26:07.119: E/AndroidRuntime(2111): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
12-30 09:26:07.119: E/AndroidRuntime(2111): at android.os.Handler.dispatchMessage(Handler.java:99)
12-30 09:26:07.119: E/AndroidRuntime(2111): at android.os.Looper.loop(Looper.java:137)
12-30 09:26:07.119: E/AndroidRuntime(2111): at android.app.ActivityThread.main(ActivityThread.java:5103)
12-30 09:26:07.119: E/AndroidRuntime(2111): at java.lang.reflect.Method.invokeNative(Native Method)
12-30 09:26:07.119: E/AndroidRuntime(2111): at java.lang.reflect.Method.invoke(Method.java:525)
12-30 09:26:07.119: E/AndroidRuntime(2111): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
12-30 09:26:07.119: E/AndroidRuntime(2111): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
12-30 09:26:07.119: E/AndroidRuntime(2111): at dalvik.system.NativeStart.main(Native Method)
12-30 09:26:07.119: E/AndroidRuntime(2111): Caused by: java.lang.NullPointerException
12-30 09:26:07.119: E/AndroidRuntime(2111): at com.techlovejump.gcm.ReceiveActivity.showList(ReceiveActivity.java:81)
12-30 09:26:07.119: E/AndroidRuntime(2111): at com.techlovejump.gcm.ReceiveActivity.onCreate(ReceiveActivity.java:49)
12-30 09:26:07.119: E/AndroidRuntime(2111): at android.app.Activity.performCreate(Activity.java:5133)
12-30 09:26:07.119: E/AndroidRuntime(2111): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
12-30 09:26:07.119: E/AndroidRuntime(2111): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
12-30 09:26:07.119: E/AndroidRuntime(2111): ... 11 more
12-30 09:26:09.999: D/dalvikvm(2111): GC_FOR_ALLOC freed 129K, 5% free 4255K/4464K, paused 129ms, total 129ms
答案 0 :(得分：0)
lvCustomList为空。你从来没有初始化它。
当你收到错误时：
lvCustomList.setAdapter(contactListAdapter);
在onCreate方法上调用setContentView后，必须对其进行初始化。