java - ASyncTask 导致 getDatabaseLocked

Question

我有一个名为 CheckForUpdates 的专用类，它扩展了 ASyncTask，用于解析来自 Internet 的 JSON 文件。创建 CheckForUpdates 类并从主 Activity 调用更新方法。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，当我尝试向数据库添加某些内容(该数据库也有一个管理它的类)时，我总是收到错误 getDatabaseLocked。我已经尝试关闭所有打开的游标和数据库，删除 MainActivity 中 CheckForUpdates 的其他实例，甚至尝试将 DatabaseHandler 实例传递给 CheckForUpdates 类，这给我带来了 nullPointerException。正如您所看到的，我已经尝试了很多方法来尝试解决这种情况，但似乎 Asynctask 正在锁定 SQLite 数据库，无论 Asynctask 的 onPostExecute 或 doInBackground() 中的编码如何。

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();
         }
     }

}

Answer 1

getDatabaseLocked()只是 SQLiteOpenHelper 中的一个方法当您传递 null 时，您会在 NPE 堆栈跟踪中看到它对于Context并正在尝试打开数据库。

null 来自哪里:CheckForUpdates有两个构造函数，其中只有另一个构造函数初始化您的 context传递给 sqlite 帮助器的成员变量。 CheckForUpdates.check()创建一个新的 CheckForUpdates使用未初始化的构造函数的实例 context 。砰。

• 删除不初始化的无参数构造函数 context .

• check()是 CheckForUpdates 的方法已经。也许它不应该创建新的 CheckForUpdates实例本身。