我有一个名为CheckForUpdates的专用类，用于扩展ASyncTask，该类可从Internet解析JSON文件。创建CheckForUpdates类，并从主活动中调用update方法。我使用一个名为DatabaseHandler的类来扩展SQLiteOpenHelper并管理数据库。但是，无论我做什么，当我尝试向数据库中添加一些也具有管理它的类的东西时，总是会收到错误getDatabaseLocked。我已经尝试关闭所有打开的游标和数据库，删除MainActivity中CheckForUpdates的另一个实例，甚至尝试将DatabaseHandler的实例传递给CheckForUpdates类，这使我得到了nullPointerException。如您所见，我已经尝试了很多方法来解决这种情况，但是无论Asynctask的onPostExecute或doInBackground()中的编码如何，Asynctask似乎都在锁定SQLite数据库。
编辑不确定内容提供商是否可以在这种情况下提供帮助，但是我想知道为什么它现在不能直接工作。
MainActivity.class
package com.andreyonadam.Contacts;
import com.andreyonadam.Contacts.R;
import android.os.Bundle;
import android.provider.Settings.Secure;
import android.annotation.SuppressLint;
import android.app.Activity;
import android.widget.Toast;
@SuppressLint("NewApi")
public class MainActivity extends Activity {
DatabaseHandler DBHandler;
CheckForUpdates CheckForUpdates;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
DBHandler = new DatabaseHandler(this);
CheckForUpdates = new CheckForUpdates(this.getApplicationContext());
CheckForUpdates.check(this, DBHandler);
}
private void databaseUpdateLists() {
// TODO Auto-generated method stub
if(!DBHandler.getAllOne().isEmpty() && !DBHandler.getAllTwo().isEmpty()){
//fetch the SQL to local Array
}else{
Toast toast = Toast.makeText(this, Integer.toString(DBHandler.getAllOne().size()), 1000);
toast.show();
//fetch the SQL to local Array
}
}
}
CheckForUpdates.class
package com.andreyonadam.Contacts;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.net.URL;
import java.util.ArrayList;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.content.Context;
import android.os.AsyncTask;
import android.util.Log;
public class CheckForUpdates extends AsyncTask<URL, Void, JSONObject> {
static InputStream is = null;
static JSONObject jObj = null;
static String json = "";
JSONArray contacts = null;
public final int version = 0;
Context context;
DatabaseHandler DBHandler;
public CheckForUpdates(Context c){
context = c;
}
public CheckForUpdates(){
}
public void check(Context c, DatabaseHandler dBHandlertemp){
context = c;
new CheckForUpdates().execute();
}
public JSONObject getJSONFromUrl(String url) {
Log.d("Update Check", "Started");
// Making HTTP request
try {
// defaultHttpClient
DefaultHttpClient httpClient = new DefaultHttpClient();
HttpPost httpPost = new HttpPost(url);
HttpResponse httpResponse = httpClient.execute(httpPost);
HttpEntity httpEntity = httpResponse.getEntity();
is = httpEntity.getContent();
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
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 + "\n");
}
is.close();
json = sb.toString();
} 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
return jObj;
}
@Override
protected JSONObject doInBackground(URL... params) {
// TODO Auto-generated method stub
JSONObject json = getJSONFromUrl("http://www.myurl.com/test/demo.json");
return json;
}
protected void onPostExecute(JSONObject jsonObj) {
DBHandler = new DatabaseHandler(context);
ArrayList<Double> one = new ArrayList<Double>();
ArrayList<Double> two = new ArrayList<Double>();
//If it wasn't able to get the JSON file it will return null
if(jsonObj != null){
try {
// Getting Array of Contacts
contacts = jsonObj.getJSONArray("test");
// looping through All Contacts
for(int i = 0; i < contacts.length(); i++){
JSONObject c = contacts.getJSONObject(i);
// Storing each json item in variable
one.add(c.getDouble("1"));
two.add(c.getDouble("2"));
//Fill array then copy
}
} catch (JSONException e) {
e.printStackTrace();
}
DBHandler.addContacts(one, two);
}
}
}
DatabaseHandler.class
package com.andreyonadam.Contacts;
import java.util.ArrayList;
import java.util.List;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.widget.Toast;
public class DatabaseHandler extends SQLiteOpenHelper {
// All Static variables
// Database Version
private static final int DATABASE_VERSION = 1;
// Database Name
private static final String DATABASE_NAME = "test";
// Contacts table name
private static final String TABLE_MAIN = "Main";
// Contacts Table Columns names
private static final String KEY_NAME = "name";
private static final String KEY_LOCATION_ONE = "one";
private static final String KEY_LOCATION_TWO = "two";
public DatabaseHandler(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
// Creating Tables
@Override
public void onCreate(SQLiteDatabase db) {
String CREATE_CONTACTS_TABLE = "CREATE TABLE " + TABLE_MAIN + " ( " +
KEY_LOCATION_ONE + " INTEGER, " +
KEY_LOCATION_TWO + " INTEGER "+ " )";
db.execSQL(CREATE_CONTACTS_TABLE);
db.close();
}
// Upgrading database
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// Drop older table if existed
db.execSQL("DROP TABLE IF EXISTS " + TABLE_MAIN);
// Create tables again
onCreate(db);
db.close();
}
public List<Double> getAllOne() {
List<Double> contactList = new ArrayList<Double>();
// Select All Query
String selectQuery = "SELECT " + KEY_LOCATION_ONE + " FROM " + TABLE_MAIN;
SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.rawQuery(selectQuery, null);
// looping through all rows and adding to list
if (cursor.moveToFirst()) {
do {
contactList.add(cursor.getDouble(0));
} while (cursor.moveToNext());
}
cursor.close();
db.close();
// return contact list
return contactList;
}
public List<Double> getAllTwo() {
List<Double> contactList = new ArrayList<Double>();
// Select All Query
String selectQuery = "SELECT * FROM " + TABLE_MAIN;
SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.rawQuery(selectQuery, null);
// looping through all rows and adding to list
if (cursor.moveToFirst()) {
do {
contactList.add(cursor.getDouble(0));
} while (cursor.moveToNext());
}
cursor.close();
db.close();
// return contact list
return contactList;
}
void addContact(Double One, Double Two) {
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(KEY_LOCATION_ONE, One); // Contact Phone
values.put(KEY_LOCATION_ONE, Two); // Contact Phone
// Inserting Row
db.insert(TABLE_MAIN, null, values);
db.close(); // Closing database connection
}
void voidAddTwo(ArrayList<Double> list){
}
void deleteAllRows(){
SQLiteDatabase db = this.getWritableDatabase();
db.delete(TABLE_MAIN, null, null);
db.close();
}
void addContacts(ArrayList<Double> one, ArrayList<Double> two){
synchronized(this) {
SQLiteDatabase db = this.getWritableDatabase();
String values = null;
for(int i = 0; i <one.size(); i++){
values = values.concat("(" + one.get(i) + ", " + two.get(i) + ")");
if(i != one.size()-1){
values.concat(",");
}
}
String CREATE_CONTACTS_TABLE = "INSERT INTO " + TABLE_MAIN + "VALUES " +
values + "";
db.execSQL(CREATE_CONTACTS_TABLE);
db.close();
}
}
}
最佳答案
getDatabaseLocked()只是SQLiteOpenHelper中的一种方法，当您为null传递了Context并尝试打开数据库时，您会在NPE堆栈跟踪中看到它。
null来自何处：CheckForUpdates有两个构造函数，只有另一个构造函数会初始化您的context成员变量，该成员变量将传递给sqlite助手。 CheckForUpdates.check()使用不初始化CheckForUpdates的构造函数创建一个新的context实例。砰。
删除不初始化context的无参数构造函数。check()是CheckForUpdates的一种方法。可能它本身不应该创建新的CheckForUpdates实例。