我使用读写数据库没有任何问题.但我无法找出差异.我在互联网上搜索但不太清楚.有人能告诉我区别吗？在哪种情况下我应该使用getWritable Database()或getReadableDatabase()？

检查 Reference

公共同步sqliteDatabase getReadableDatabase()

自：API级别1

Create and/or open a database. This will be the same object returned
by getWritableDatabase() unless some problem,such as a full disk,
requires the database to be opened read-only. In that case,a
read-only database object will be returned. If the problem is fixed,a
future call to getWritableDatabase() may succeed,in which case the
read-only database object will be closed and the read/write object
will be returned in the future.

与getWritableDatabase()一样,此方法可能需要很长时间才能返回,因此您不应从应用程序主线程(包括ContentProvider.onCreate())调用它.
返回

a database object valid until getWritableDatabase() or close() is called.

抛出
sqliteException如果无法打开数据库

公共同步sqliteDatabase getWritableDatabase()

自：API级别1

Create and/or open a database that will be used for reading and
writing. The first time this is called,the database will be opened
and onCreate(sqliteDatabase),onUpgrade(sqliteDatabase,int,int)
and/or onopen(sqliteDatabase) will be called.

Once opened successfully,the database is cached,so you can call this
method every time you need to write to the database. (Make sure to
call close() when you no longer need the database.) Errors such as bad
permissions or a full disk may cause this method to fail,but future
attempts may succeed if the problem is fixed.

数据库升级可能需要很长时间,您不应该从应用程序主线程调用此方法,包括从ContentProvider.onCreate().
返回

a read/write database object valid until close() is called

抛出sqliteException如果无法打开数据库进行写入

我收到了错误

02-15 08:36:13.097: I/sqliteDatabaseCpp(404): sqlite returned: error
code = 1,msg = near “null”: Syntax error,
db=/data/data/com.lifeApp/databases/contactsManager

在我的代码的第157行.这是该方法下的部分

getAllContacts()

无效的代码是

sqliteDatabase db = this.getWritableDatabase();

完整示例：

package com.lifeApp;

import android.content.Context;
import android.database.sqlite.sqliteDatabase;
import android.database.sqlite.sqliteOpenHelper;

import java.util.ArrayList;
import java.util.List;

import android.content.ContentValues;
import android.database.Cursor;

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 = "contactsManager";

   // Contacts table name
   private static final String TABLE_CONTACTS = "contacts";

   // Contacts Table Columns names
   private static final String KEY_ID = "id";
   private static final String FirsTNAME = "firstname";
   private static final String LASTNAME = "lastname";
   private static final String PASSWORD = "password";
   private static final String EMAIL = "email";

   private static final String KEY_PH_NO = "phone_number";

private static final String KEY_NAME = null;

   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_CONTACTS + "("
               + KEY_ID + " INTEGER PRIMARY KEY," 
               + KEY_NAME + " TEXT,"
               + FirsTNAME + " TEXT,"
               + LASTNAME + " TEXT,"
               + PASSWORD  + " TEXT"
               + EMAIL + " TEXT"
               + KEY_PH_NO + " TEXT" + ")";
       db.execsql(CREATE_CONTACTS_TABLE);
   }

   // Upgrading database
   @Override
   public void onUpgrade(sqliteDatabase db,int oldVersion,int newVersion) {
       // Drop older table if existed
       db.execsql("DROP TABLE IF EXISTS " + TABLE_CONTACTS);

       // Create tables again
       onCreate(db);
   }

   /**
    * All CRUD(Create,Read,Update,Delete) Operations
    */

   // Adding new contact
   void addContact(Contact contact) {
       sqliteDatabase db = this.getWritableDatabase();

       ContentValues values = new ContentValues();
       values.put(KEY_NAME,contact.getName()); // Contact Name
       values.put(FirsTNAME,contact.getFirstname());
       values.put(LASTNAME,contact.getLastname());
       values.put(EMAIL,contact.getEmail());
       values.put(PASSWORD,contact.getpassword());
       values.put(KEY_PH_NO,contact.getPhoneNumber()); // Contact Phone

       // Inserting Row
       db.insert(TABLE_CONTACTS,values);
       db.close(); // Closing database connection
   }

   // Getting single contact
   Contact getContact(int id) {
       sqliteDatabase db = this.getReadableDatabase();

       Cursor cursor = db.query(TABLE_CONTACTS,new String[] { KEY_ID,KEY_NAME,KEY_PH_NO },KEY_ID + "=?",new String[] { String.valueOf(id) },null);
       if (cursor != null)
           cursor.movetoFirst();

       Contact contact = new Contact(Integer.parseInt(cursor.getString(0)),cursor.getString(1),cursor.getString(2),cursor.getString(3),cursor.getString(4),cursor.getString(5),cursor.getString(6));
       // return contact
       return contact;
   }

   // Getting All Contacts
   public List<Contact> getAllContacts() {
       List<Contact> contactList = new ArrayList<Contact>();
       // Select All Query
       String selectQuery = "SELECT  * FROM " + TABLE_CONTACTS;

       sqliteDatabase db = this.getWritableDatabase();
       Cursor cursor = db.rawQuery(selectQuery,null);

       // looping through all rows and adding to list
       if (cursor.movetoFirst()) {
           do {
               Contact contact = new Contact();
               contact.setID(Integer.parseInt(cursor.getString(0)));
               contact.setFirstname(cursor.getString(1));
               contact.setLastname(cursor.getString(2));
               contact.setPassword(cursor.getString(3));
               contact.setEmail(cursor.getString(4));
               // Adding contact to list
               contactList.add(contact);
           } while (cursor.movetoNext());
       }

       // return contact list
       return contactList;
   }

   // Updating single contact
   public int updateContact(Contact contact) {
       sqliteDatabase db = this.getWritableDatabase();

       ContentValues values = new ContentValues();
       values.put(KEY_NAME,contact.getName());
       values.put(FirsTNAME,contact.getLastname());
       values.put(PASSWORD,contact.getpassword());
       values.put(EMAIL,contact.getEmail());
       values.put(KEY_PH_NO,contact.getPhoneNumber());

       // updating row
       return db.update(TABLE_CONTACTS,values,KEY_ID + " = ?",new String[] { String.valueOf(contact.getID()) });
   }

   // Deleting single contact
   public void deleteContact(Contact contact) {
       sqliteDatabase db = this.getWritableDatabase();
       db.delete(TABLE_CONTACTS,new String[] { String.valueOf(contact.getID()) });
       db.close();
   }

   // Getting contacts Count
   public int getContactsCount() {
       String countQuery = "SELECT  * FROM " + TABLE_CONTACTS;
       sqliteDatabase db = this.getReadableDatabase();
       Cursor cursor = db.rawQuery(countQuery,null);
       cursor.close();

       // return count
       return cursor.getCount();
   }

}

在CREATE_CONTACTS_TABLE中,您会遗漏一些逗号

String CREATE_CONTACTS_TABLE = "CREATE TABLE " + TABLE_CONTACTS + "("
           + KEY_ID + " INTEGER PRIMARY KEY," 
           + KEY_NAME + " TEXT,"
           + FirsTNAME + " TEXT,"
           + LASTNAME + " TEXT,"
           + PASSWORD  + " TEXT"           <==
           + EMAIL + " TEXT"               <==
           + KEY_PH_NO + " TEXT" + ")";
   db.execsql(CREATE_CONTACTS_TABLE);

这两种方法有什么区别吗？两者都返回一个打开的sqlite Database.如果不存在,则两者都可以创建数据库.当需要读/写时,sqliteOpenHelper也有getWriteableDatabase …

我应该使用哪种方法？基于我见过的示例代码,我首先使用sqliteOpenHelper创建数据库,但在需要使用数据库时调用sqliteDatabase.openDatabase.

openDatabase()更灵活,允许您指定区域设置等,但在大多数情况下,您不需要显式提供这些详细信息,Android documentation说使用getReadableDatabase()和getWriteableDatabase().