android sqlite的事务

* There are two kinds of transaction: implicit transactions and explicit
* transactions.
* </p><p>
* An implicit transaction is created whenever a database operation is requested
* and there is no explicit transaction currently in progress.  An implicit transaction
* only lasts for the duration of the database operation in question and then it
* is ended.  If the database operation was successful, then its changes are committed.
* </p><p>
* An explicit transaction is started by calling {@link #beginTransaction} and
* specifying the desired transaction mode.  Once an explicit transaction has begun,
* all subsequent database operations will be performed as part of that transaction.
* To end an explicit transaction, first call {@link #setTransactionSuccessful} if the
* transaction was successful, then call {@link #end}.  If the transaction was
* marked successful, its changes will be committed, otherwise they will be rolled back.
* </p><p>
* Explicit transactions can also be nested.  A nested explicit transaction is
* started with {@link #beginTransaction}, marked successful with
* {@link #setTransactionSuccessful}and ended with {@link #endTransaction}.
* If any nested transaction is not marked successful, then the entire transaction
* including all of its nested transactions will be rolled back

* when the outermost transaction is ended.

for example:----------------------

db.execSQL("update person set amount=amount-10 where personid=?", new Object[]{1});  

or.....

6.  db.beginTransaction();  

7.     try  

8.     {  

9.         db.execSQL("update person set amount=amount-10 where personid=?", new Object[]{1});  

10.         db.execSQL("update person set amount=amount+10 where personid=?", new Object[]{2});  

11.         //设置事务标志为成功，当结束事务时就会提交事务  

12.         db.setTransactionSuccessful();  
13.     }  

14.    catch（Exception e）{
15.         throw(e);

16.     }

17.     finally  
18.     {  

19.         //结束事务  

20.         db.endTransaction();  
20. }