blocks|key|280460|text|DBHelper类处理sqlite数据库的打开和关闭以及sa的创建和更新，here是一篇关于它是如何工作的很好的文章。当我开始使用android的时候，它非常有用(然而，我最近使用了objective-c，忘记了它的大部分用途。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|280461|entityMap|0|LINK|mutability|MUTABLE|url|http://www.vogella.com/articles/AndroidSQLite/article.html^0|11|4|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

The DBHelper class is what handles the opening and closing of sqlite databases as well sa creation and updating, and a decent article on how it all works is <a href="http://www.vogella.com/articles/AndroidSQLite/article.html" rel="nofollow">here</a>. When I started android it was very useful (however I've been objective-c lately, and forgotten most of it to be any use.

blocks|key|280513|text|使用Helper类，您可以访问SQLite数据库，并可以通过覆盖onCreate()和onUpgrade()方法对其执行各种操作。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|280514|http://technologyguid.com/android-sqlite-database-app-example/|offset|length|280515|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|1Q|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@$D|O|E|P|1|Q]]|A|$]]|$1|F|3|-4|5|6|7|R|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|C]]]]

Using Helper class you can access SQLite Database and can perform the various operations on it by overriding the onCreate() and onUpgrade() methods.

<a href="http://technologyguid.com/android-sqlite-database-app-example/" rel="nofollow noreferrer">http://technologyguid.com/android-sqlite-database-app-example/</a>

blocks|key|497388|text|Sqlite+helper类帮助我们管理数据库创建和版本管理。SQLiteOpenHelper负责所有数据库管理活动。要使用它，|type|unstyled|depth|inlineStyleRanges|entityRanges|data|497389|1.重写SQLiteOpenHelper的onCreate(),+onUpgrade()方法。可以选择覆盖onOpen()方法。|offset|length|style|CODE|497390|2.使用这个子类创建一个可读或可写的数据库，并使用SQLiteDatabase的四个insert(),+execSQL(),+update(),+delete()方法来创建、读取、更新和删除表中的行。|497391|创建MyEmployees表以及选择和插入记录的示例：|497392|public+class+MyDatabaseHelper+extends+SQLiteOpenHelper+{

++++private+static+final+String+DATABASE_NAME+=+"DBName";

++++private+static+final+int+DATABASE_VERSION+=+2;

++++//+Database+creation+sql+statement
++++private+static+final+String+DATABASE_CREATE+=+"create+table+MyEmployees
+++++++++++++++++++++++++++++++++(+_id+integer+primary+key,name+text+not+null);";

++++public+MyDatabaseHelper(Context+context)+{
++++++++super(context,+DATABASE_NAME,+null,+DATABASE_VERSION);
++++}

++++//+Method+is+called+during+creation+of+the+database
++++@Override
++++public+void+onCreate(SQLiteDatabase+database)+{
++++++++database.execSQL(DATABASE_CREATE);
++++}

++++//+Method+is+called+during+an+upgrade+of+the+database,
++++@Override
++++public+void+onUpgrade(SQLiteDatabase+database,int+oldVersion,int+newVersion){
++++++++Log.w(MyDatabaseHelper.class.getName(),
+++++++++++++++++++++++++"Upgrading+database+from+version+"+%2B+oldVersion+%2B+"+to+"
+++++++++++++++++++++++++%2B+newVersion+%2B+",+which+will+destroy+all+old+data");
++++++++database.execSQL("DROP+TABLE+IF+EXISTS+MyEmployees");
++++++++onCreate(database);
++++}
}|code-block|syntax|javascript|497393|现在您可以使用这个类，如下所示：|497394|public+class+MyDB{++

++++private+MyDatabaseHelper+dbHelper;++

++++private+SQLiteDatabase+database;++

++++public+final+static+String+EMP_TABLE="MyEmployees";+//+name+of+table+

++++public+final+static+String+EMP_ID="_id";+//+id+value+for+employee
++++public+final+static+String+EMP_NAME="name";++//+name+of+employee

++++/**+
+++++*+
+++++*+@param+context+
+++++*/++
++++public+MyDB(Context+context){++
++++++++dbHelper+=+new+MyDatabaseHelper(context);++
++++++++database+=+dbHelper.getWritableDatabase();++
++++}


++++public+long+createRecords(String+id,+String+name){++
++++++++ContentValues+values+=+new+ContentValues();++
++++++++values.put(EMP_ID,+id);++
++++++++values.put(EMP_NAME,+name);++
++++++++return+database.insert(EMP_TABLE,+null,+values);++
++++}++++

++++public+Cursor+selectRecords()+{
++++++++String[]+cols+=+new+String[]+{EMP_ID,+EMP_NAME};++
++++++++Cursor+mCursor+=+database.query(true,+EMP_TABLE,cols,null++
++++++++++++,+null,+null,+null,+null,+null);++
++++++++if+(mCursor+!=+null)+{++
++++++++++++mCursor.moveToFirst();++
++++++++}++
++++++++return+mCursor;+//+iterate+to+get+each+value.
++++}
}|497395|现在，您可以在活动中使用MyDB类来执行所有的数据库操作。创建记录将帮助您插入值，类似地，您可以使用自己的更新和删除函数。|497396|entityMap^0|0|4|G|L|N|0|16|13|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Z|8|@$D|10|E|11|F|G]|$D|12|E|13|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|14|8|@$D|15|E|16|F|G]]|9|@]|A|$]]|$1|J|3|K|5|6|7|17|8|@]|9|@]|A|$]]|$1|L|3|M|5|N|7|18|8|@]|9|@]|A|$O|P]]|$1|Q|3|R|5|6|7|19|8|@]|9|@]|A|$]]|$1|S|3|T|5|N|7|1A|8|@]|9|@]|A|$O|P]]|$1|U|3|V|5|6|7|1B|8|@]|9|@]|A|$]]|$1|W|3|-4|5|6|7|1C|8|@]|9|@]|A|$]]]|X|$]]

Sqlite helper class helps us to manage database creation and version management.
SQLiteOpenHelper takes care of all database management activities. To use it, 
 1.Override <code>onCreate(), onUpgrade()</code> methods of <code>SQLiteOpenHelper</code>. Optionally override onOpen() method.
 2.Use this subclass to create either a readable or writable database and use the SQLiteDatabase's four API methods <code>insert(), execSQL(), update(), delete()</code> to create, read, update and delete rows of your table.

Example to create a MyEmployees table and to select and insert records: 

<pre><code>public class MyDatabaseHelper extends SQLiteOpenHelper {

 private static final String DATABASE_NAME = "DBName";

 private static final int DATABASE_VERSION = 2;

 // Database creation sql statement
 private static final String DATABASE_CREATE = "create table MyEmployees
 ( _id integer primary key,name text not null);";

 public MyDatabaseHelper(Context context) {
 super(context, DATABASE_NAME, null, DATABASE_VERSION);
 }

 // Method is called during creation of the database
 @Override
 public void onCreate(SQLiteDatabase database) {
 database.execSQL(DATABASE_CREATE);
 }

 // Method is called during an upgrade of the database,
 @Override
 public void onUpgrade(SQLiteDatabase database,int oldVersion,int newVersion){
 Log.w(MyDatabaseHelper.class.getName(),
 "Upgrading database from version " + oldVersion + " to "
 + newVersion + ", which will destroy all old data");
 database.execSQL("DROP TABLE IF EXISTS MyEmployees");
 onCreate(database);
 }
}
</code></pre>

Now you can use this class as below,

<pre><code>public class MyDB{ 

 private MyDatabaseHelper dbHelper; 

 private SQLiteDatabase database; 

 public final static String EMP_TABLE="MyEmployees"; // name of table 

 public final static String EMP_ID="_id"; // id value for employee
 public final static String EMP_NAME="name"; // name of employee

 /** 
 * 
 * @param context 
 */ 
 public MyDB(Context context){ 
 dbHelper = new MyDatabaseHelper(context); 
 database = dbHelper.getWritableDatabase(); 
 }


 public long createRecords(String id, String name){ 
 ContentValues values = new ContentValues(); 
 values.put(EMP_ID, id); 
 values.put(EMP_NAME, name); 
 return database.insert(EMP_TABLE, null, values); 
 } 

 public Cursor selectRecords() {
 String[] cols = new String[] {EMP_ID, EMP_NAME}; 
 Cursor mCursor = database.query(true, EMP_TABLE,cols,null 
 , null, null, null, null, null); 
 if (mCursor != null) { 
 mCursor.moveToFirst(); 
 } 
 return mCursor; // iterate to get each value.
 }
}
</code></pre>

Now you can use MyDB class in you activity to have all the database operations. The create records will help you to insert the values similarly you can have your own functions for update and delete.

I am new to Android and I have to create an application where I need to use a SQLite database.
I am not so well equipped with the SQLite.

Could you tell me what the purpose and use of the <code>SQLiteOpenHelper</code> class, and provide a simple database creation and insertion example?

Android SQLite Example

数据库管理

数据库

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我是安卓新手，我必须创建一个需要使用SQLite数据库的应用程序。我对SQLite的装备不是很好。您能否告诉我SQLiteOpenHelper类的用途和用法，并提供一个简单的数据库创建和插入示例？

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