【发布时间】：2017-01-25 09:46:54
【问题描述】：
我正在尝试在广播（CONNECTIVITY_CHANGE）发生时进行一些数据库操作，当我的应用程序运行正常时，但在应用程序被杀死后它给出了异常：
09-17 12:10:01.175 31502-31515/com.example.deepak.broadcastrecieverswithdatabase W/System.err: java.lang.NullPointerException
09-17 12:10:01.175 31502-31515/com.example.deepak.broadcastrecieverswithdatabase W/System.err: at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:224)
09-17 12:10:01.175 31502-31515/com.example.deepak.broadcastrecieverswithdatabase W/System.err: at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:164)
09-17 12:10:01.175 31502-31515/com.example.deepak.broadcastrecieverswithdatabase W/System.err: at com.example.deepak.broadcastrecieverswithdatabase.Operations.doInBackground(Operations.java:43)
09-17 12:10:01.175 31502-31515/com.example.deepak.broadcastrecieverswithdatabase W/System.err: at com.example.deepak.broadcastrecieverswithdatabase.Operations.doInBackground(Operations.java:14)
09-17 12:10:01.175 31502-31515/com.example.deepak.broadcastrecieverswithdatabase W/System.err: at android.os.AsyncTask$2.call(AsyncTask.java:288)
09-17 12:10:01.185 31502-31515/com.example.deepak.broadcastrecieverswithdatabase W/System.err: at java.util.concurrent.FutureTask.run(FutureTask.java:237)
09-17 12:10:01.185 31502-31515/com.example.deepak.broadcastrecieverswithdatabase W/System.err: at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
09-17 12:10:01.185 31502-31515/com.example.deepak.broadcastrecieverswithdatabase W/System.err: at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
09-17 12:10:01.185 31502-31515/com.example.deepak.broadcastrecieverswithdatabase W/System.err: at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
09-17 12:10:01.185 31502-31515/com.example.deepak.broadcastrecieverswithdatabase W/System.err: at java.lang.Thread.run(Thread.java:841)
我最近开始开发安卓应用，谁能帮我解决这个问题？此外，任何有关优化我的代码的提示将不胜感激。 我的代码是这样的：
package com.example.deepak.broadcastrecieverswithdatabase;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.os.AsyncTask;
import java.util.ArrayList;
import java.util.List;
public class Operations extends AsyncTask<String, String, List<Integer>> {
DBHelper dbHelper;
SQLiteDatabase db;
Cursor cursor;
List<Integer> counterList;
public static final String DB_NAME = "db_name.db";
public static final int VERSION = 1;
public static final String TABLE = "counters";
public static final String COUNTER1 = "counter1";
public static final String COUNTER2 = "counter2";
String opType = "";
Context context = null;
String operation;
int counter1, counter2;
ContentValues contentValues;
public Operations(MainActivity activity, String operation, String opType, int counter1, int counter2){
if(activity!=null)
this.context = activity.getApplicationContext();
this.operation = operation;
this.counter1 = counter1;
this.counter2 = counter2;
this.opType = opType;
}
@Override
protected List<Integer> doInBackground(String... strings) {
try {
dbHelper = new DBHelper();
db = dbHelper.getWritableDatabase();
switch (operation) {
case "insert":
contentValues = new ContentValues();
contentValues.put(COUNTER1, counter1);
contentValues.put(COUNTER2, counter2);
db.insertWithOnConflict(TABLE, null, contentValues, SQLiteDatabase.CONFLICT_IGNORE);
break;
case "update":
counterList = new ArrayList<>();
Cursor cursor1 = getCursor();
try {
cursor.moveToFirst();
while (!cursor.isAfterLast()) {
counterList.add(Integer.parseInt(cursor.getString(cursor.getColumnIndex("counter1"))));
counterList.add(Integer.parseInt(cursor.getString(cursor.getColumnIndex("counter2"))));
cursor.moveToNext();
}
} finally {
cursor.close();
}
counter1 = counterList.get(0);
counter2 = counterList.get(1);
if(opType.equals("alwaysOn"))
{
counter1++;
}
else
{
counter2++;
}
if (counter1 > 0) {
contentValues = new ContentValues();
contentValues.put(COUNTER1, counter1);
contentValues.put(COUNTER2, counter2);
db.update(TABLE, contentValues, COUNTER1 + "=" + (counter1 - 1), null);
}
List<Integer> counters = new ArrayList<>();
counters.add(counter1);
counters.add(counter2);
return counters;
case "get":
counterList = new ArrayList<>();
Cursor cursor = getCursor();
try {
cursor.moveToFirst();
while (!cursor.isAfterLast()) {
counterList.add(Integer.parseInt(cursor.getString(cursor.getColumnIndex("counter1"))));
counterList.add(Integer.parseInt(cursor.getString(cursor.getColumnIndex("counter2"))));
cursor.moveToNext();
}
return counterList;
} finally {
cursor.close();
}
}
}catch (Exception npe)
{npe.printStackTrace();} finally {
dbHelper.close();
}
return null;
}
public Cursor getCursor(){
cursor = db.query(TABLE, null, null, null, null, null, null);
return cursor;
}
@Override
protected void onPostExecute(List<Integer> counterList) {
super.onPostExecute(counterList);
if(counterList!=null && context!=null) {
MainActivity.alwaysOnValue.setText(""+counterList.get(0));
MainActivity.onDemandValue.setText(""+counterList.get(1));
}
}
class DBHelper extends SQLiteOpenHelper {
public DBHelper() {
super(context, DB_NAME, null, VERSION);
}
@Override
public void onCreate(SQLiteDatabase sqLiteDatabase) {
String sql = String.format("create table %s"+"(%s int primary key, %s int)", TABLE, COUNTER1,COUNTER2);
sqLiteDatabase.execSQL(sql);
}
@Override
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int oldVersion, int newVersion) {
sqLiteDatabase.execSQL("drop table if exists "+ TABLE);
onCreate(sqLiteDatabase);
}
}
}
【问题讨论】：
-
没有帮助，
-
因为你还不知道如何管理 NPE。了解 NPE 是什么以及它为什么会发生。然后你就会看到光明。
-
我试图寻找这个，经过一段时间的搜索，我找到了 NPE 的原因（之前我正在发送活动，但是当应用程序被杀死时，不会有任何我没想到的活动，但是广播接收器的受限上下文将在那里，所以现在我正在发送它，这解决了我的问题），现在我更正了它，谢谢，但是对于学习者（像我一样），你应该更详细一点，无论如何谢谢大家.
标签： android database sqlite nullpointerexception android-sqlite