我们知道数据库创建的时候默认保存到系统data/data/项目名 下面了，有没有一种方法保存到自己指定的SDCard上的文件夹里面呢？答案是可以的。我们只需要找到SQLiteOpenHelper这个类，了解一下就不难发现其保存的路径是固定了的，那么我们只需要改动一下getWritableDatabase()，即写入的时候的路径：
public synchronized SQLiteDatabase getWritableDatabase() {
if (mDatabase != null && mDatabase.isOpen() && !mDatabase.isReadOnly()) {
return mDatabase; // The database is already open for business
}
if (mIsInitializing) {
throw new IllegalStateException("getWritableDatabase called recursively");
}
// If we have a read-only database open, someone could be using it
// (though they shouldn't), which would cause a lock to be held on
// the file, and our attempts to open the database read-write would
// fail waiting for the file lock. To prevent that, we acquire the
// lock on the read-only database, which shuts out other users.
boolean success = false;
SQLiteDatabase db = null;
if (mDatabase != null) mDatabase.lock();
try {
mIsInitializing = true;
if (mName == null) {
db = SQLiteDatabase.create(null);
} else {
db = mContext.openOrCreateDatabase(mName, 0, mFactory);
}
int version = db.getVersion();
if (version != mNewVersion) {
db.beginTransaction();
try {
if (version == 0) {
onCreate(db);
} else {
onUpgrade(db, version, mNewVersion);
}
db.setVersion(mNewVersion);
db.setTransactionSuccessful();
} finally {
db.endTransaction();
}
}
onOpen(db);
success = true;
return db;
} finally {
mIsInitializing = false;
if (success) {
if (mDatabase != null) {
try { mDatabase.close(); } catch (Exception e) { }
mDatabase.unlock();
}
mDatabase = db;
} else {
if (mDatabase != null) mDatabase.unlock();
if (db != null) db.close();
}
}
}
注意标志的红色的部分，这是创建数据库的地方，我们再看看openOrCreateDatabase（）
这个方法，openOrCreateDatabase（）这个方法存在于package android.content;下面的public abstract class Context{}类里面，
public abstract SQLiteDatabase openOrCreateDatabase(String name,int mode, CursorFactory factory);
我们发现在package android.database.sqlite;包下的public class SQLiteDatabase extends SQLiteClosable {}里面也有一个
public static SQLiteDatabase openOrCreateDatabase(String path, CursorFactory factory) {
return openDatabase(path, factory, CREATE_IF_NECESSARY);
}
相同的方法，只是参数不同，这个可以传一个路径进去，我们就调用这个方法。
然后我们还要有一个我们指定文件夹的路径的方法：
public File getDatabasePath(String name) {
String EXTERN_PATH = null;
//判断是否有SDcard
if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)==true)
{
//判断是否存在指定的文件夹，如果没有就创建它
EXTERN_PATH = android.os.Environment.getExternalStorageDirectory().getAbsolutePath()
+ "/database/";
File f=new File(EXTERN_PATH);
if(!f.exists())
{
f.mkdirs();
}
}
return new File(EXTERN_PATH+ name);
}
及对SDcard进行写和读的权限：
<!-- 在SDCard中创建于删除文件权限 -->
<uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS" />
<!-- 往SDCard写入数据权限 -->
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
最后当我们创建数据库的时候直接继承我们自己定义的SDSQLiteOpenHelper（），不用系统自带SQLiteOpenHelper（）即可。
参考我在eoeAndroid中文章：http://www.eoeandroid.com/thread-53985-1-1.html
自已定义的SDSQLiteOpenHelper（）：
public abstract class SDSQLiteOpenHelper {
private static final String TAG = SDSQLiteOpenHelper.class.getSimpleName();
@SuppressWarnings("unused")
private final Context mContext;
private final String mName;
private final CursorFactory mFactory;
private final int mNewVersion;
private SQLiteDatabase mDatabase = null;
private boolean mIsInitializing = false;
/**
* Create a helper object to create, open, and/or manage a database. The
* database is not actually created or opened until one of
* {@link #getWritableDatabase} or {@link #getReadableDatabase} is called.
*
* @param context
* to use to open or create the database
* @param name
* of the database file, or null for an in-memory database
* @param factory
* to use for creating cursor objects, or null for the default
* @param version
* number of the database (starting at 1); if the database is
* older, {@link #onUpgrade} will be used to upgrade the database
*/
public SDSQLiteOpenHelper(Context context, String name,
CursorFactory factory, int version) {
if (version < 1)
throw new IllegalArgumentException("Version must be >= 1, was "
+ version);
mContext = context;
mName = name;
mFactory = factory;
mNewVersion = version;
}
/**
* Create and/or open a database that will be used for reading and writing.
* 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
* {@link #close} when you no longer need it.
*
* <p>
* Errors such as bad permissions or a full disk may cause this operation to
* fail, but future attempts may succeed if the problem is fixed.
* </p>
*
* @throws SQLiteException
* if the database cannot be opened for writing
* @return a read/write database object valid until {@link #close} is called
*/
public synchronized SQLiteDatabase getWritableDatabase() {
if (mDatabase != null && mDatabase.isOpen() && !mDatabase.isReadOnly()) {
return mDatabase; // The database is already open for business
}
if (mIsInitializing) {
throw new IllegalStateException(
"getWritableDatabase called recursively");
}
// If we have a read-only database open, someone could be using it
// (though they shouldn't), which would cause a lock to be held on
// the file, and our attempts to open the database read-write would
// fail waiting for the file lock. To prevent that, we acquire the
// lock on the read-only database, which shuts out other users.
boolean success = false;
SQLiteDatabase db = null;
try {
mIsInitializing = true;
if (mName == null) {
db = SQLiteDatabase.create(null);
} else {
String path = getDatabasePath(mName).getPath();
db = SQLiteDatabase.openOrCreateDatabase(path, mFactory);
}
int version = db.getVersion();
if (version != mNewVersion) {
db.beginTransaction();
try {
if (version == 0) {
onCreate(db);
} else {
onUpgrade(db, version, mNewVersion);
}
db.setVersion(mNewVersion);
db.setTransactionSuccessful();
} finally {
db.endTransaction();
}
}
onOpen(db);
success = true;
return db;
} finally {
mIsInitializing = false;
if (success) {
if (mDatabase != null) {
try {
mDatabase.close();
} catch (Exception e) {
}
}
mDatabase = db;
} else {
if (db != null)
db.close();
}
}
}
/**
* Create and/or open a database. This will be the same object returned by
* {@link #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 {@link #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.
*
* @throws SQLiteException
* if the database cannot be opened
* @return a database object valid until {@link #getWritableDatabase} or
* {@link #close} is called.
*/
public synchronized SQLiteDatabase getReadableDatabase() {
if (mDatabase != null && mDatabase.isOpen()) {
return mDatabase; // The database is already open for business
}
if (mIsInitializing) {
throw new IllegalStateException(
"getReadableDatabase called recursively");
}
try {
return getWritableDatabase();
} catch (SQLiteException e) {
if (mName == null)
throw e; // Can't open a temp database read-only!
Log.e(TAG, "Couldn't open " + mName
+ " for writing (will try read-only):", e);
}
SQLiteDatabase db = null;
try {
mIsInitializing = true;
String path = getDatabasePath(mName).getPath();
db = SQLiteDatabase.openDatabase(path, mFactory,
SQLiteDatabase.OPEN_READWRITE);
if (db.getVersion() != mNewVersion) {
throw new SQLiteException(
"Can't upgrade read-only database from version "
+ db.getVersion() + " to " + mNewVersion + ": "
+ path);
}
onOpen(db);
Log.w(TAG, "Opened " + mName + " in read-only mode");
mDatabase = db;
return mDatabase;
} finally {
mIsInitializing = false;
if (db != null && db != mDatabase)
db.close();
}
}
/**
* Close any open database object.
*/
public synchronized void close() {
if (mIsInitializing)
throw new IllegalStateException("Closed during initialization");
if (mDatabase != null && mDatabase.isOpen()) {
mDatabase.close();
mDatabase = null;
}
}
public File getDatabasePath(String name) {
String EXTERN_PATH = null;
if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)==true)
{
EXTERN_PATH = android.os.Environment.getExternalStorageDirectory().getAbsolutePath()
+ "/db/";
File f=new File(EXTERN_PATH);
if(!f.exists())
{
f.mkdirs();
}
}
return new File(EXTERN_PATH+ name);
}
/**
* Called when the database is created for the first time. This is where the
* creation of tables and the initial population of the tables should
* happen.
*
* @param db
* The database.
*/
public abstract void onCreate(SQLiteDatabase db);
/**
* Called when the database needs to be upgraded. The implementation should
* use this method to drop tables, add tables, or do anything else it needs
* to upgrade to the new schema version.
*
* <p>
* The SQLite ALTER TABLE documentation can be found <a
* href="http://sqlite.org/lang_altertable.html">here</a>. If you add new
* columns you can use ALTER TABLE to insert them into a live table. If you
* rename or remove columns you can use ALTER TABLE to rename the old table,
* then create the new table and then populate the new table with the
* contents of the old table.
*
* @param db
* The database.
* @param oldVersion
* The old database version.
* @param newVersion
* The new database version.
*/
public abstract void onUpgrade(SQLiteDatabase db, int oldVersion,
int newVersion);
/**
* Called when the database has been opened. Override method should check
* {@link SQLiteDatabase#isReadOnly} before updating the database.
*
* @param db
* The database.
*/
public void onOpen(SQLiteDatabase db) {
}
}