无法从资产中复制预先创建的数据库
Can't copy pre-created db from assets
android 无法从资产复制我预先创建的数据库，旧数据库仍然存在于 data/data/packagename/dabases，我想用新数据库更改旧数据库
ive tried to change this.getReadableDatabase(); into SQLiteDatabse db = this.getReadabledatabase()
if (db.isOpen()){
db.close();
}
public void createDatabase(){
boolean dbExist = checkDatabase();
if(!dbExist){
this.getReadableDatabase();
SQl
try {
copyDatabase();
}catch (IOException e){
Log.e(this.getClass().toString(),"eror kopi");
throw new Error("error kopi");
}
}else{
Log.i(this.getClass().toString(),"databse udah ada");
}
}
private void copyDatabase() throws IOException {
InputStream externalDBStream =
context.getAssets().open(DATABASE_NAME);
String outFileName = DB_PATH + DATABASE_NAME;
OutputStream localDBStream = new FileOutputStream(outFileName);
byte[] buffer = new byte[1024];
int bytesRead;
while ((bytesRead = externalDBStream.read(buffer)) > 0) {
localDBStream.write(buffer, 0, bytesRead);
}
localDBStream.flush();
localDBStream.close();
externalDBStream.close();
}
我希望使用我预先创建的数据库
你有很多问题，假设你想用另一个副本替换现有的预先存在的数据库。
您面临的问题是，由于存在数据库，因此复制将不会继续，即 checkDatabase() 将 return 为真。
如果您只是简单地调用 copyDatabase()，那么每次应用 运行 时都会复制数据库，如果数据库可以由用户修改。
你需要做的是有一个指标，可以测试，看看是否已经改变了预先存在的数据库。有多种方法，但最 likely/common 的方法是利用 SQLite user_version。这是一个整数值，经常用于通过 onUpgrade 方法更新当前数据库。
作为打开数据库的一部分，SQLiteOpenHelper（因此是其子类）将存储在数据库中的 user_version 与提供的版本号（[= 的第 4 个参数）进行比较122=]iteOpenHelper 超级调用），如果后者大于数据库中存储的值，则调用 onUpgrade 方法。 （如果相反，那么 onDowngrade 方法将被调用，并且在没有被编码的情况下会发生异常）。
user_version可以在SQL站点管理工具用户SQLPRAGMA user_version = n.
中设置
另一个问题是，从Android9开始，数据库默认以WAL（Write-Ahead Logging）模式打开。使用 this.getReadableDatabase(); 的上述代码导致创建 -shm 和 -wal 文件。它们的存在会导致陷入错误（因为它们与复制的数据库不匹配），然后导致 SQLiteOpenHelper 创建一个空的（理论上可用的数据库）基本上擦除复制的数据库（我相信这就是发生的事情).
之所以使用this.getReadableDatabase();是因为它解决了当没有应用程序数据时，数据库 folder/directory没有的问题t 存在并使用上面的创建它。正确的方法是创建数据库 directory/folder 如果它不存在。因此，不会创建 -wal 和 -shm 文件。
以下是一个 DatabseHelper 示例，它克服了这些问题，并且还允许根据更改 user_version.
复制预先存在的数据库的修改版本
public class DBHelperV001 extends SQLiteOpenHelper {
public static final String DBNAME = "test.db"; //<<<<<<<<<< obviously change accordingly
//
private static int db_user_version, asset_user_version, user_version_offset = 60, user_version_length = 4;
private static String stck_trc_msg = " (see stack-trace above)";
private static String sqlite_ext_journal = "-journal";
private static String sqlite_ext_shm = "-shm";
private static String sqlite_ext_wal = "-wal";
private static int copy_buffer_size = 1024 * 8; //Copy data in 8k chucks, change if wanted.
SQLiteDatabase mDB;
/**
* Instantiate the DBHelper, copying the databse from the asset folder if no DB exists
* or if the user_version is greater than the user_version of the current database.
* NOTE The pre-existing database copied into the assets folder MUST have the user version set
* to 1 or greater. If the user_version in the assets folder is increased above the
*
* @param context
*/
public DBHelperV001(Context context) {
// Note get the version according to the asset file
// avoid having to maintain the version number passed
super(context, DBNAME, null, setUserVersionFromAsset(context,DBNAME));
if (!ifDbExists(context,DBNAME)) {
copyDBFromAssets(context, DBNAME,DBNAME);
} else {
setUserVersionFromAsset(context,DBNAME);
setUserVersionFromDB(context,DBNAME);
if (asset_user_version > db_user_version) {
copyDBFromAssets(context,DBNAME,DBNAME);
}
}
// Force open (and hence copy attempt) when constructing helper
mDB = this.getWritableDatabase();
}
@Override
public void onCreate(SQLiteDatabase db) {
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
@Override
public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
/**
* Check to see if the databse file exists
* @param context The Context
* @param dbname The databse name
* @return true id database file exists, else false
*/
private static boolean ifDbExists(Context context, String dbname) {
File db = context.getDatabasePath(dbname);
if (db.exists()) return true;
if (!db.getParentFile().exists()) {
db.getParentFile().mkdirs();
}
return false;
}
/**
* set the db_user_version according to the user_version obtained from the current database file
* @param context The Context
* @param dbname The database (file) name
* @return The user_version
*/
private static int setUserVersionFromDB(Context context, String dbname) {
File db = context.getDatabasePath(dbname);
InputStream is;
try {
is = new FileInputStream(db);
} catch (IOException e) {
throw new RuntimeException("IOError Opening " + db.getPath() + " as an InputStream" + stck_trc_msg);
}
db_user_version = getUserVersion(is);
Log.d("DATABASEUSERVERSION","Obtained user_version from current DB, it is " + String.valueOf(db_user_version)); //TODO remove for live App
return db_user_version;
}
/**
* set the asset_user_version according to the user_version from the asset file
* @param context
* @param assetname
* @return
*/
private static int setUserVersionFromAsset(Context context, String assetname) {
InputStream is;
try {
is = context.getAssets().open(assetname);
} catch (IOException e) {
e.printStackTrace();
throw new RuntimeException("IOError Getting asset " + assetname + " as an InputStream" + stck_trc_msg);
}
asset_user_version = getUserVersion(is);
Log.d("ASSETUSERVERSION","Obtained user_version from asset, it is " + String.valueOf(asset_user_version)); //TODO remove for Live App
return asset_user_version;
}
/**
* Retrieve SQLite user_version from the provied InputStream
* @param is The InputStream
* @return the user_version
*/
private static int getUserVersion(InputStream is) {
String ioerrmsg = "Reading DB header bytes(60-63) ";
int rv;
byte[] buffer = new byte[user_version_length];
byte[] header = new byte[64];
try {
is.skip(user_version_offset);
is.read(buffer,0,user_version_length);
ByteBuffer bb = ByteBuffer.wrap(buffer);
rv = ByteBuffer.wrap(buffer).getInt();
ioerrmsg = "Closing DB ";
is.close();
return rv;
} catch (IOException e) {
e.printStackTrace();
throw new RuntimeException("IOError " + ioerrmsg + stck_trc_msg);
}
}
/**
* Copy the database file from the assets
* Note backup of existing files may not be required
* @param context The Context
* @param dbname The database (file)name
* @param assetname The asset name (may therefore be different but )
*/
private static void copyDBFromAssets(Context context, String dbname, String assetname) {
String tag = "COPYDBFROMASSETS";
Log.d(tag,"Copying Database from assets folder");
String backup_base = "bkp_" + String.valueOf(System.currentTimeMillis());
String ioerrmsg = "Opening Asset " + assetname;
// Prepare Files that could be used
File db = context.getDatabasePath(dbname);
File dbjrn = new File(db.getPath() + sqlite_ext_journal);
File dbwal = new File(db.getPath() + sqlite_ext_wal);
File dbshm = new File(db.getPath() + sqlite_ext_shm);
File dbbkp = new File(db.getPath() + backup_base);
File dbjrnbkp = new File(db.getPath() + backup_base);
File dbwalbkp = new File(db.getPath() + backup_base);
File dbshmbkp = new File(db.getPath() + backup_base);
byte[] buffer = new byte[copy_buffer_size];
int bytes_read = 0;
int total_bytes_read = 0;
int total_bytes_written = 0;
// Backup existing sqlite files
if (db.exists()) {
db.renameTo(dbbkp);
dbjrn.renameTo(dbjrnbkp);
dbwal.renameTo(dbwalbkp);
dbshm.renameTo(dbshmbkp);
}
// ALWAYS delete the additional sqlite log files
dbjrn.delete();
dbwal.delete();
dbshm.delete();
//Attempt the copy
try {
ioerrmsg = "Open InputStream for Asset " + assetname;
InputStream is = context.getAssets().open(assetname);
ioerrmsg = "Open OutputStream for Databse " + db.getPath();
OutputStream os = new FileOutputStream(db);
ioerrmsg = "Read/Write Data";
while((bytes_read = is.read(buffer)) > 0) {
total_bytes_read = total_bytes_read + bytes_read;
os.write(buffer,0,bytes_read);
total_bytes_written = total_bytes_written + bytes_read;
}
ioerrmsg = "Flush Written data";
os.flush();
ioerrmsg = "Close DB OutputStream";
os.close();
ioerrmsg = "Close Asset InputStream";
is.close();
Log.d(tag,"Databsse copied from the assets folder. " + String.valueOf(total_bytes_written) + " bytes were copied.");
// Delete the backups
dbbkp.delete();
dbjrnbkp.delete();
dbwalbkp.delete();
dbshmbkp.delete();
} catch (IOException e) {
e.printStackTrace();
throw new RuntimeException("IOError attempting to " + ioerrmsg + stck_trc_msg);
}
}
}
用法示例
考虑以下资产文件（sqlite 数据库）（警告，因为它们是应用程序将失败）：-
所以有两个数据库（使用 PRAGMA user_version = 1 和 PRAGMA user_version = 2 respectively/according 设置的 user_version 与文件名相同）
对于全新的，第一次 运行 应用程序（即卸载）然后文件 test.dbV1 重命名为 test.db 并使用以下 activity :-
public class MainActivity extends AppCompatActivity {
DBHelperV001 mDbhlpr;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mDbhlpr = new DBHelperV001(this);
DatabaseUtils.dumpCursor(
mDbhlpr.getWritableDatabase().query(
"sqlite_master",
null,null,null,null,null,null
)
);
}
}
- 这只是实例化数据库助手（它将复制或使用数据库）然后转储 sqlite_master table.
日志包含：-
04-02 12:55:36.258 644-644/aaa.so55441840 D/ASSETUSERVERSION: Obtained user_version from asset, it is 1
04-02 12:55:36.258 644-644/aaa.so55441840 D/COPYDBFROMASSETS: Copying Database from assets folder
04-02 12:55:36.262 644-644/aaa.so55441840 D/COPYDBFROMASSETS: Databsse copied from the assets folder. 69632 bytes were copied.
04-02 12:55:36.265 644-644/aaa.so55441840 I/System.out: >>>>> Dumping cursor android.database.sqlite.SQLiteCursor@d121f9c
04-02 12:55:36.265 644-644/aaa.so55441840 I/System.out: 0 {
04-02 12:55:36.265 644-644/aaa.so55441840 I/System.out: type=table
04-02 12:55:36.265 644-644/aaa.so55441840 I/System.out: name=android_metadata
04-02 12:55:36.265 644-644/aaa.so55441840 I/System.out: tbl_name=android_metadata
04-02 12:55:36.265 644-644/aaa.so55441840 I/System.out: rootpage=3
04-02 12:55:36.265 644-644/aaa.so55441840 I/System.out: sql=CREATE TABLE android_metadata (locale TEXT)
04-02 12:55:36.266 644-644/aaa.so55441840 I/System.out: }
04-02 12:55:36.266 644-644/aaa.so55441840 I/System.out: 1 {
04-02 12:55:36.266 644-644/aaa.so55441840 I/System.out: type=table
04-02 12:55:36.266 644-644/aaa.so55441840 I/System.out: name=shops
..........
引入新版本DB时，user_version为2
- 即test.db 原 test.dbV1 重命名为 test.dbV1 然后，
- （有效删除）
- test.dbV2然后重命名为test.db
- （有效引入新资产文件）然后：-
然后应用程序重新运行然后日志包含：-
04-02 13:04:25.044 758-758/? D/ASSETUSERVERSION: Obtained user_version from asset, it is 2
04-02 13:04:25.046 758-758/? D/ASSETUSERVERSION: Obtained user_version from asset, it is 2
04-02 13:04:25.046 758-758/? D/DATABASEUSERVERSION: Obtained user_version from current DB, it is 1
04-02 13:04:25.047 758-758/? D/COPYDBFROMASSETS: Copying Database from assets folder
04-02 13:04:25.048 758-758/? D/COPYDBFROMASSETS: Databsse copied from the assets folder. 69632 bytes were copied.
04-02 13:04:25.051 758-758/? I/System.out: >>>>> Dumping cursor android.database.sqlite.SQLiteCursor@25012da5
04-02 13:04:25.052 758-758/? I/System.out: 0 {
04-02 13:04:25.052 758-758/? I/System.out: type=table
04-02 13:04:25.052 758-758/? I/System.out: name=android_metadata
04-02 13:04:25.052 758-758/? I/System.out: tbl_name=android_metadata
04-02 13:04:25.052 758-758/? I/System.out: rootpage=3
04-02 13:04:25.052 758-758/? I/System.out: sql=CREATE TABLE android_metadata (locale TEXT)
04-02 13:04:25.052 758-758/? I/System.out: }
04-02 13:04:25.052 758-758/? I/System.out: 1 {
04-02 13:04:25.052 758-758/? I/System.out: type=table
04-02 13:04:25.052 758-758/? I/System.out: name=shops
最后，随后的 运行 即没有更新的资产，日志显示：-
04-02 13:05:50.197 840-840/aaa.so55441840 D/ASSETUSERVERSION: Obtained user_version from asset, it is 2
04-02 13:05:50.198 840-840/aaa.so55441840 D/ASSETUSERVERSION: Obtained user_version from asset, it is 2
04-02 13:05:50.198 840-840/aaa.so55441840 D/DATABASEUSERVERSION: Obtained user_version from current DB, it is 2
04-02 13:05:50.201 840-840/aaa.so55441840 I/System.out: >>>>> Dumping cursor android.database.sqlite.SQLiteCursor@d121f9c
04-02 13:05:50.202 840-840/aaa.so55441840 I/System.out: 0 {
04-02 13:05:50.202 840-840/aaa.so55441840 I/System.out: type=table
04-02 13:05:50.202 840-840/aaa.so55441840 I/System.out: name=android_metadata
04-02 13:05:50.202 840-840/aaa.so55441840 I/System.out: tbl_name=android_metadata
04-02 13:05:50.202 840-840/aaa.so55441840 I/System.out: rootpage=3
04-02 13:05:50.202 840-840/aaa.so55441840 I/System.out: sql=CREATE TABLE android_metadata (locale TEXT)
04-02 13:05:50.202 840-840/aaa.so55441840 I/System.out: }
04-02 13:05:50.202 840-840/aaa.so55441840 I/System.out: 1 {
04-02 13:05:50.202 840-840/aaa.so55441840 I/System.out: type=table
04-02 13:05:50.202 840-840/aaa.so55441840 I/System.out: name=shops
即没有复制，因为资产实际上是相同的
android 无法从资产复制我预先创建的数据库，旧数据库仍然存在于 data/data/packagename/dabases，我想用新数据库更改旧数据库
ive tried to change this.getReadableDatabase(); into SQLiteDatabse db = this.getReadabledatabase()
if (db.isOpen()){
db.close();
}
public void createDatabase(){
boolean dbExist = checkDatabase();
if(!dbExist){
this.getReadableDatabase();
SQl
try {
copyDatabase();
}catch (IOException e){
Log.e(this.getClass().toString(),"eror kopi");
throw new Error("error kopi");
}
}else{
Log.i(this.getClass().toString(),"databse udah ada");
}
}
private void copyDatabase() throws IOException {
InputStream externalDBStream =
context.getAssets().open(DATABASE_NAME);
String outFileName = DB_PATH + DATABASE_NAME;
OutputStream localDBStream = new FileOutputStream(outFileName);
byte[] buffer = new byte[1024];
int bytesRead;
while ((bytesRead = externalDBStream.read(buffer)) > 0) {
localDBStream.write(buffer, 0, bytesRead);
}
localDBStream.flush();
localDBStream.close();
externalDBStream.close();
}
我希望使用我预先创建的数据库
你有很多问题，假设你想用另一个副本替换现有的预先存在的数据库。
您面临的问题是，由于存在数据库，因此复制将不会继续，即 checkDatabase() 将 return 为真。
如果您只是简单地调用 copyDatabase()，那么每次应用 运行 时都会复制数据库，如果数据库可以由用户修改。
你需要做的是有一个指标，可以测试，看看是否已经改变了预先存在的数据库。有多种方法，但最 likely/common 的方法是利用 SQLite user_version。这是一个整数值，经常用于通过 onUpgrade 方法更新当前数据库。
作为打开数据库的一部分，SQLiteOpenHelper（因此是其子类）将存储在数据库中的 user_version 与提供的版本号（[= 的第 4 个参数）进行比较122=]iteOpenHelper 超级调用），如果后者大于数据库中存储的值，则调用 onUpgrade 方法。 （如果相反，那么 onDowngrade 方法将被调用，并且在没有被编码的情况下会发生异常）。
user_version可以在SQL站点管理工具用户SQLPRAGMA user_version = n.
另一个问题是，从Android9开始，数据库默认以WAL（Write-Ahead Logging）模式打开。使用 this.getReadableDatabase(); 的上述代码导致创建 -shm 和 -wal 文件。它们的存在会导致陷入错误（因为它们与复制的数据库不匹配），然后导致 SQLiteOpenHelper 创建一个空的（理论上可用的数据库）基本上擦除复制的数据库（我相信这就是发生的事情).
之所以使用this.getReadableDatabase();是因为它解决了当没有应用程序数据时，数据库 folder/directory没有的问题t 存在并使用上面的创建它。正确的方法是创建数据库 directory/folder 如果它不存在。因此，不会创建 -wal 和 -shm 文件。
以下是一个 DatabseHelper 示例，它克服了这些问题，并且还允许根据更改 user_version.
复制预先存在的数据库的修改版本public class DBHelperV001 extends SQLiteOpenHelper {
public static final String DBNAME = "test.db"; //<<<<<<<<<< obviously change accordingly
//
private static int db_user_version, asset_user_version, user_version_offset = 60, user_version_length = 4;
private static String stck_trc_msg = " (see stack-trace above)";
private static String sqlite_ext_journal = "-journal";
private static String sqlite_ext_shm = "-shm";
private static String sqlite_ext_wal = "-wal";
private static int copy_buffer_size = 1024 * 8; //Copy data in 8k chucks, change if wanted.
SQLiteDatabase mDB;
/**
* Instantiate the DBHelper, copying the databse from the asset folder if no DB exists
* or if the user_version is greater than the user_version of the current database.
* NOTE The pre-existing database copied into the assets folder MUST have the user version set
* to 1 or greater. If the user_version in the assets folder is increased above the
*
* @param context
*/
public DBHelperV001(Context context) {
// Note get the version according to the asset file
// avoid having to maintain the version number passed
super(context, DBNAME, null, setUserVersionFromAsset(context,DBNAME));
if (!ifDbExists(context,DBNAME)) {
copyDBFromAssets(context, DBNAME,DBNAME);
} else {
setUserVersionFromAsset(context,DBNAME);
setUserVersionFromDB(context,DBNAME);
if (asset_user_version > db_user_version) {
copyDBFromAssets(context,DBNAME,DBNAME);
}
}
// Force open (and hence copy attempt) when constructing helper
mDB = this.getWritableDatabase();
}
@Override
public void onCreate(SQLiteDatabase db) {
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
@Override
public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
/**
* Check to see if the databse file exists
* @param context The Context
* @param dbname The databse name
* @return true id database file exists, else false
*/
private static boolean ifDbExists(Context context, String dbname) {
File db = context.getDatabasePath(dbname);
if (db.exists()) return true;
if (!db.getParentFile().exists()) {
db.getParentFile().mkdirs();
}
return false;
}
/**
* set the db_user_version according to the user_version obtained from the current database file
* @param context The Context
* @param dbname The database (file) name
* @return The user_version
*/
private static int setUserVersionFromDB(Context context, String dbname) {
File db = context.getDatabasePath(dbname);
InputStream is;
try {
is = new FileInputStream(db);
} catch (IOException e) {
throw new RuntimeException("IOError Opening " + db.getPath() + " as an InputStream" + stck_trc_msg);
}
db_user_version = getUserVersion(is);
Log.d("DATABASEUSERVERSION","Obtained user_version from current DB, it is " + String.valueOf(db_user_version)); //TODO remove for live App
return db_user_version;
}
/**
* set the asset_user_version according to the user_version from the asset file
* @param context
* @param assetname
* @return
*/
private static int setUserVersionFromAsset(Context context, String assetname) {
InputStream is;
try {
is = context.getAssets().open(assetname);
} catch (IOException e) {
e.printStackTrace();
throw new RuntimeException("IOError Getting asset " + assetname + " as an InputStream" + stck_trc_msg);
}
asset_user_version = getUserVersion(is);
Log.d("ASSETUSERVERSION","Obtained user_version from asset, it is " + String.valueOf(asset_user_version)); //TODO remove for Live App
return asset_user_version;
}
/**
* Retrieve SQLite user_version from the provied InputStream
* @param is The InputStream
* @return the user_version
*/
private static int getUserVersion(InputStream is) {
String ioerrmsg = "Reading DB header bytes(60-63) ";
int rv;
byte[] buffer = new byte[user_version_length];
byte[] header = new byte[64];
try {
is.skip(user_version_offset);
is.read(buffer,0,user_version_length);
ByteBuffer bb = ByteBuffer.wrap(buffer);
rv = ByteBuffer.wrap(buffer).getInt();
ioerrmsg = "Closing DB ";
is.close();
return rv;
} catch (IOException e) {
e.printStackTrace();
throw new RuntimeException("IOError " + ioerrmsg + stck_trc_msg);
}
}
/**
* Copy the database file from the assets
* Note backup of existing files may not be required
* @param context The Context
* @param dbname The database (file)name
* @param assetname The asset name (may therefore be different but )
*/
private static void copyDBFromAssets(Context context, String dbname, String assetname) {
String tag = "COPYDBFROMASSETS";
Log.d(tag,"Copying Database from assets folder");
String backup_base = "bkp_" + String.valueOf(System.currentTimeMillis());
String ioerrmsg = "Opening Asset " + assetname;
// Prepare Files that could be used
File db = context.getDatabasePath(dbname);
File dbjrn = new File(db.getPath() + sqlite_ext_journal);
File dbwal = new File(db.getPath() + sqlite_ext_wal);
File dbshm = new File(db.getPath() + sqlite_ext_shm);
File dbbkp = new File(db.getPath() + backup_base);
File dbjrnbkp = new File(db.getPath() + backup_base);
File dbwalbkp = new File(db.getPath() + backup_base);
File dbshmbkp = new File(db.getPath() + backup_base);
byte[] buffer = new byte[copy_buffer_size];
int bytes_read = 0;
int total_bytes_read = 0;
int total_bytes_written = 0;
// Backup existing sqlite files
if (db.exists()) {
db.renameTo(dbbkp);
dbjrn.renameTo(dbjrnbkp);
dbwal.renameTo(dbwalbkp);
dbshm.renameTo(dbshmbkp);
}
// ALWAYS delete the additional sqlite log files
dbjrn.delete();
dbwal.delete();
dbshm.delete();
//Attempt the copy
try {
ioerrmsg = "Open InputStream for Asset " + assetname;
InputStream is = context.getAssets().open(assetname);
ioerrmsg = "Open OutputStream for Databse " + db.getPath();
OutputStream os = new FileOutputStream(db);
ioerrmsg = "Read/Write Data";
while((bytes_read = is.read(buffer)) > 0) {
total_bytes_read = total_bytes_read + bytes_read;
os.write(buffer,0,bytes_read);
total_bytes_written = total_bytes_written + bytes_read;
}
ioerrmsg = "Flush Written data";
os.flush();
ioerrmsg = "Close DB OutputStream";
os.close();
ioerrmsg = "Close Asset InputStream";
is.close();
Log.d(tag,"Databsse copied from the assets folder. " + String.valueOf(total_bytes_written) + " bytes were copied.");
// Delete the backups
dbbkp.delete();
dbjrnbkp.delete();
dbwalbkp.delete();
dbshmbkp.delete();
} catch (IOException e) {
e.printStackTrace();
throw new RuntimeException("IOError attempting to " + ioerrmsg + stck_trc_msg);
}
}
}
用法示例
考虑以下资产文件（sqlite 数据库）（警告，因为它们是应用程序将失败）：-
所以有两个数据库（使用 PRAGMA user_version = 1 和 PRAGMA user_version = 2 respectively/according 设置的 user_version 与文件名相同）
对于全新的，第一次 运行 应用程序（即卸载）然后文件 test.dbV1 重命名为 test.db 并使用以下 activity :-
public class MainActivity extends AppCompatActivity {
DBHelperV001 mDbhlpr;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mDbhlpr = new DBHelperV001(this);
DatabaseUtils.dumpCursor(
mDbhlpr.getWritableDatabase().query(
"sqlite_master",
null,null,null,null,null,null
)
);
}
}
- 这只是实例化数据库助手（它将复制或使用数据库）然后转储 sqlite_master table.
日志包含：-
04-02 12:55:36.258 644-644/aaa.so55441840 D/ASSETUSERVERSION: Obtained user_version from asset, it is 1
04-02 12:55:36.258 644-644/aaa.so55441840 D/COPYDBFROMASSETS: Copying Database from assets folder
04-02 12:55:36.262 644-644/aaa.so55441840 D/COPYDBFROMASSETS: Databsse copied from the assets folder. 69632 bytes were copied.
04-02 12:55:36.265 644-644/aaa.so55441840 I/System.out: >>>>> Dumping cursor android.database.sqlite.SQLiteCursor@d121f9c
04-02 12:55:36.265 644-644/aaa.so55441840 I/System.out: 0 {
04-02 12:55:36.265 644-644/aaa.so55441840 I/System.out: type=table
04-02 12:55:36.265 644-644/aaa.so55441840 I/System.out: name=android_metadata
04-02 12:55:36.265 644-644/aaa.so55441840 I/System.out: tbl_name=android_metadata
04-02 12:55:36.265 644-644/aaa.so55441840 I/System.out: rootpage=3
04-02 12:55:36.265 644-644/aaa.so55441840 I/System.out: sql=CREATE TABLE android_metadata (locale TEXT)
04-02 12:55:36.266 644-644/aaa.so55441840 I/System.out: }
04-02 12:55:36.266 644-644/aaa.so55441840 I/System.out: 1 {
04-02 12:55:36.266 644-644/aaa.so55441840 I/System.out: type=table
04-02 12:55:36.266 644-644/aaa.so55441840 I/System.out: name=shops
..........
引入新版本DB时，user_version为2
- 即test.db 原 test.dbV1 重命名为 test.dbV1 然后，
- （有效删除）
- test.dbV2然后重命名为test.db
- （有效引入新资产文件）然后：-
然后应用程序重新运行然后日志包含：-
04-02 13:04:25.044 758-758/? D/ASSETUSERVERSION: Obtained user_version from asset, it is 2
04-02 13:04:25.046 758-758/? D/ASSETUSERVERSION: Obtained user_version from asset, it is 2
04-02 13:04:25.046 758-758/? D/DATABASEUSERVERSION: Obtained user_version from current DB, it is 1
04-02 13:04:25.047 758-758/? D/COPYDBFROMASSETS: Copying Database from assets folder
04-02 13:04:25.048 758-758/? D/COPYDBFROMASSETS: Databsse copied from the assets folder. 69632 bytes were copied.
04-02 13:04:25.051 758-758/? I/System.out: >>>>> Dumping cursor android.database.sqlite.SQLiteCursor@25012da5
04-02 13:04:25.052 758-758/? I/System.out: 0 {
04-02 13:04:25.052 758-758/? I/System.out: type=table
04-02 13:04:25.052 758-758/? I/System.out: name=android_metadata
04-02 13:04:25.052 758-758/? I/System.out: tbl_name=android_metadata
04-02 13:04:25.052 758-758/? I/System.out: rootpage=3
04-02 13:04:25.052 758-758/? I/System.out: sql=CREATE TABLE android_metadata (locale TEXT)
04-02 13:04:25.052 758-758/? I/System.out: }
04-02 13:04:25.052 758-758/? I/System.out: 1 {
04-02 13:04:25.052 758-758/? I/System.out: type=table
04-02 13:04:25.052 758-758/? I/System.out: name=shops
最后，随后的 运行 即没有更新的资产，日志显示：-
04-02 13:05:50.197 840-840/aaa.so55441840 D/ASSETUSERVERSION: Obtained user_version from asset, it is 2
04-02 13:05:50.198 840-840/aaa.so55441840 D/ASSETUSERVERSION: Obtained user_version from asset, it is 2
04-02 13:05:50.198 840-840/aaa.so55441840 D/DATABASEUSERVERSION: Obtained user_version from current DB, it is 2
04-02 13:05:50.201 840-840/aaa.so55441840 I/System.out: >>>>> Dumping cursor android.database.sqlite.SQLiteCursor@d121f9c
04-02 13:05:50.202 840-840/aaa.so55441840 I/System.out: 0 {
04-02 13:05:50.202 840-840/aaa.so55441840 I/System.out: type=table
04-02 13:05:50.202 840-840/aaa.so55441840 I/System.out: name=android_metadata
04-02 13:05:50.202 840-840/aaa.so55441840 I/System.out: tbl_name=android_metadata
04-02 13:05:50.202 840-840/aaa.so55441840 I/System.out: rootpage=3
04-02 13:05:50.202 840-840/aaa.so55441840 I/System.out: sql=CREATE TABLE android_metadata (locale TEXT)
04-02 13:05:50.202 840-840/aaa.so55441840 I/System.out: }
04-02 13:05:50.202 840-840/aaa.so55441840 I/System.out: 1 {
04-02 13:05:50.202 840-840/aaa.so55441840 I/System.out: type=table
04-02 13:05:50.202 840-840/aaa.so55441840 I/System.out: name=shops
即没有复制，因为资产实际上是相同的