安卓开发中怎么修改数据库中的数据

public

class

DatabaseHelper

extends

SQLiteOpenHelper

{

private

static

DatabaseHelper

mInstance

=

null

/**

数据库名称

**/

public

static

final

String

DATABASE_NAME

=

"xys.db"

/**

数据库版本号

**/

private

static

final

int

DATABASE_VERSION

=

1

/**数据库SQL语句

添加一个表**/

private

static

final

String

NAME_TABLE_CREATE

=

"create

table

test("

+

"_id

INTEGER

PRIMARY

KEY

AUTOINCREMENT,"

+

"name

TEXT,"+"hp

INTEGER

DEFAULT

100,"+

"mp

INTEGER

DEFAULT

100,"

+

"number

INTEGER)"

DatabaseHelper(Context

context)

{

super(context,

DATABASE_NAME,

null,

DATABASE_VERSION)

}

/**单例模式**/

static

synchronized

DatabaseHelper

getInstance(Context

context)

{

if

(mInstance

==

null)

{

mInstance

=

new

DatabaseHelper(context)

}

return

mInstance

}

@Override

public

void

onCreate(SQLiteDatabase

db)

{

/**向数据中添加表**/

db.execSQL(NAME_TABLE_CREATE)

}

@Override

public

void

onUpgrade(SQLiteDatabase

db,

int

oldVersion,

int

newVersion)

{

/**可以拿到当前数据库的版本信息

与之前数据库的版本信息

用来更新数据库**/

}

/**

*

删除数据库

*

@param

context

*

@return

*/

public

boolean

deleteDatabase(Context

context)

{

return

context.deleteDatabase(DATABASE_NAME)

}

}

These files will be ones that get deleted first when the device runs low on storage. There is no guarantee when these files will be deleted.

但是，最好不要依赖系统来管理，应该自己设定一个最大容量，当超出这个值时自己删除。

Context.getFilesDir(),Context.openFileOutput(String, int),Context.getFileStreamPath(String),Context.getDir(String, int)

/data/data/files

Android支持在SD卡上的应用私有目录，在Froyo版本后，通过getExternalFilesDir()可以获得具体路径。该路径依赖与应用的包名，如果你包为hello.file那么SD开上的应用私有目录为\mnt\sdcard\Android\data\hello.file\files\.

在使用SD卡目录时，需注意SD卡是否挂载，可通过Environment.getExternalStorageState()方法进行判断，如果返回值为Envirnment.MEDIA_MOUNTED表示SD卡处于挂载状态，可以放心使用。

getExternalCacheDir()和getCacheDir()比较

共同点：

files will be deleted when the application is uninstalled

不同点：

1、The platform does not monitor the space available in external storage, and thus will not automatically delete these files. Note that you should be managing the maximum space you will use for these anyway, just like with getCacheDir().

2、External files are not always available: they will disappear if the user mounts the external storage on a computer or removes it. See the APIs on Environment for information in the storage state.

3、There is no security enforced with these files. All applications can read and write files placed here.

---