關(guān)于android sqlite database存儲(chǔ)到sdcard上的問題

點(diǎn)點(diǎn)滴滴 2012-04-28

展開全文

關(guān)于android sqlite database存儲(chǔ)到sdcard上的問題 [復(fù)制鏈接]

發(fā)表于 2010-7-23 10:36:55 |只看該作者 |倒序?yàn)g覽

分享有獎(jiǎng)： 0

最近碰到apk和后臺(tái)的cpp code都需要訪問一個(gè)數(shù)據(jù)庫的問題。結(jié)果發(fā)現(xiàn)apk中創(chuàng)建的數(shù)據(jù)庫外部的進(jìn)程是沒有權(quán)限去讀/寫的。這就需要把數(shù)據(jù)庫文件創(chuàng)建到sdcard上。
后來發(fā)現(xiàn)在SQLiteOpenHelper(frameworks/base/core/java/android/database/sqlite /SQLiteOpenHelper.java)這個(gè)類中，創(chuàng)建數(shù)據(jù)庫文件的路徑是使用傳入的contex的getDatabasePath獲取的，這個(gè) 是不允許修改的（至少我沒有找到）。
那我就仿照這個(gè)SQLiteOpenHelper寫了一個(gè)abstract class SDSQLiteOpenHelper，其使用和SQLiteOpenHelper一樣，然后只要加上相應(yīng)的permission，這樣就可以實(shí)現(xiàn)把數(shù)據(jù)庫存儲(chǔ)到sdcard上了。

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.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.
* For an example, see the NotePadProvider class in the NotePad sample application,
* in the samples/ directory of the SDK.
*/
public abstract class SDSQLiteOpenHelper {
private static final String TAG = SDSQLiteOpenHelper.class.getSimpleName();
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.
*
* 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.
*
* @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.DatabopenOrCreatease(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)
{
return new File("/sdcard/" + 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.
*
* The SQLite ALTER TABLE documentation can be found
* <a href="http:///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) {}
}

復(fù)制代碼

改動(dòng)的部分我就不標(biāo)識(shí)出來了，有興趣可以去研究下源碼。

本站是提供個(gè)人知識(shí)管理的網(wǎng)絡(luò)存儲(chǔ)空間，所有內(nèi)容均由用戶發(fā)布，不代表本站觀點(diǎn)。請注意甄別內(nèi)容中的聯(lián)系方式、誘導(dǎo)購買等信息，謹(jǐn)防詐騙。如發(fā)現(xiàn)有害或侵權(quán)內(nèi)容，請點(diǎn)擊一鍵舉報(bào)。

轉(zhuǎn)藏 分享

QQ空間 QQ好友新浪微博微信

獻(xiàn)花（0） +1

來自：點(diǎn)點(diǎn)滴滴 > 《android》

舉報(bào)/認(rèn)領(lǐng)