SDSQliteOpenHelper将数据库建立在SD卡上

有的时候，做一些软件时因为数据库文件较大，如果采取内置的数据库是不可取的，这时我们可以引用别人写的SDSQliteHelper
SDSqliteHelper跟系统的SQliteHelper操作差不多，只有一个地方不同
不同点：
SDSQliteHelper的数据库名称要带格式如sqlite.db
而系统的SqliteHelper的数据库不用带格式，直接文件名如sqlite

SDSQliteHelper.java内容如下，使用的时候只需，复制SDSQliteHelper.java文件到相应包，其他的操作参考系统引用SQliteHelper的例子或参考http://7071976.blog.51cto.com/blog/7061976/1232364

import java.io.File;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.os.Environment;
import android.util.Log;
/**
* A helper class to manage database creation and version management.
* You create a subclass implementing {@link #onCreate}, {@link #onUpgrade} and
* optionally {@link #onOpen}, and this class takes care of opening the database
* if it exists, creating it if it does not, and upgrading it as necessary.
* Transactions are used to make sure the database is always in a sensible state.
* <p>For an example, see the NotePadProvider class in the NotePad sample application,
* in the <em>samples/</em> directory of the SDK.</p>
*/
public abstract class SDSQLiteOpenHelper {
private static final String TAG = SDSQLiteOpenHelper.class.getSimpleName();
public static String sdcardpath;
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)//得到数据库位置可以看需求相应更改
{
if(this.ExistSDCard()){
sdcardpath = Environment.getExternalStorageDirectory().getPath()+"/";

}
return new File(sdcardpath+ 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) {}

private boolean ExistSDCard() {  //判断SD卡是否存在
Log.d("Exitsdcard",String.valueOf(android.os.Environment.getExternalStorageState().equals(
android.os.Environment.MEDIA_MOUNTED)));
if (android.os.Environment.getExternalStorageState().equals(
android.os.Environment.MEDIA_MOUNTED)) {
return true;
} else
return false;
}
}