问题描述
这是我的代码，
public DBHelper(Context context) {
super(context, DB_NAME, null, 2);
this.context = context;
DB_PATH = context.getDatabasePath(DB_NAME).getAbsolutePath();
}
@Override
public void onCreate(SQLiteDatabase db) {
createDataBase();
}
private void createDataBase() {
boolean dbExist = checkDataBase();
if (!dbExist) {
copyDataBase();
}
}
private boolean checkDataBase() {
System.out.println("DB_PATH : " + DB_PATH);
File dbFile = new File(DB_PATH);
return dbFile.exists();
}
private void copyDataBase() {
Log.i("Database",
"New database is being copied to device!");
byte[] buffer = new byte[1024];
OutputStream myOutput;
int length;
InputStream myInput;
try {
myInput = context.getAssets().open(DB_NAME);
myOutput = new FileOutputStream(DB_PATH);
while ((length = myInput.read(buffer)) > 0) {
myOutput.write(buffer, 0, length);
}
myOutput.close();
myOutput.flush();
myInput.close();
Log.i("Database",
"New database has been copied to device!");
} catch (IOException e) {
e.printStackTrace();
}
}
一切正常，我什至得到日志New database has been copied to device!，但是当我尝试从db读取数据时，却出现了no such table异常.
Everything works fine, and I even get the log New database has been copied to device!, but when I try to read the data from db, I am getting no such table exception.
注意:我正在尝试更新我的一个旧应用程序，该代码在5.0和更低版本的旧设备版本中也可以使用，但是当我尝试使用最新设备更新该应用程序时，该代码无法正常工作.
Note: I'm trying to update one of my old app, this same code works in older device versions like 5.0 and below, but when I try to update the app using latest devices its not working.
推荐答案
假设您复制到资产文件夹的数据库确实包含该表，那么我认为您的问题是您正在实例化该实例. DBHelper，然后通过隐式或显式调用getWritableDatabase或getReadableDatabase隐式打开数据库，然后使用 onCreate 方法启动副本.
Assuming that the database you have copied to the assets folder does contain the table(s) then I believe that your issue is that you are instantiating an instance of the DBHelper and then you have implicitly opened the database by either implicitly or explicitly calling getWritableDatabase or getReadableDatabase and are then using the onCreate method to initiate the copy.
如果是这样，则get?ableDatabase将创建一个空数据库，副本将覆盖此数据库，但是在更高版本的Android 9+上，-shm和-wal文件将保留原样，并且在数据库建立时保留打开，然后由于-shm和-wal文件与原始的空数据库不匹配，因此检测到损坏，因此当SDK代码尝试提供可用的数据库时，创建的新数据库为空.
If so then the get????ableDatabase will create an empty database, the copy overwrites this but on later versions, Android 9+, the -shm and -wal files are left as they were and when the database is then opened, then due to the -shm and -wal files not matching the original empty database a corruption is detected so a new database is created that is empty, as the SDK code tries to provide a usable database.
- 默认情况下，从Android 9+开始，默认情况下使用 WAL(提前写入日志)，这就是创建和使用-shm和-wal文件的原因.
- From Android 9+ by default WAL (Write Ahead Logging) is used by default, this is what creates and uses the -shm and -wal files.
有3个修复程序.
-
使用 disableWriteAheadLogging 方法通过重写SQLiteOpenHelper类的onConfigure方法.然后，它将使用较旧的日记模式.
use the disableWriteAheadLogging method by overriding the onConfigure method of the SQLiteOpenHelper class. This then uses the older journal mode.
确保未调用getWritableDatabase/getReadableDatabase.这可以通过确保在实例化DBHelper实例时完成复制来完成.
Ensure that getWritableDatabase/getReadableDatabase is not called. This could be done by ensuring the copy is done when instantiating the DBHelper instance.
确保-wal和-shm文件(如果在复制时存在)被删除.
Ensuring that the -wal and -shm files, if they exist at the time of the copy, are deleted.
使用第一种方法可能只会延迟不可避免的情况，因此不建议这样做，因为它没有利用WAL模式的好处.
Using the first is perhaps only delaying the inevitable and is not really recommended as it does not take advantage of the benefits of WAL mode.
以下版本的DBHelper包含第二个修订，并且作为预防措施还包含了第三个修订:-
The following version of your DBHelper incorporates the second fixand also as a precaution the third fix :-
public class DBHelper extends SQLiteOpenHelper {
public static final String DB_NAME = "myDBName";
public static String DB_PATH;
Context context;
public DBHelper(Context context) {
super(context, DB_NAME, null, 2);
this.context = context;
//<<<<<<<<<< ADDED (moved from createDatabase) 1st Fix >>>>>>>>>>
DB_PATH = context.getDatabasePath(DB_NAME).getAbsolutePath();
if (!checkDataBase()) {
copyDataBase();
}
//<<<<<<<<<< END OF ADDED CODE >>>>>>>>>>
this.getWritableDatabase(); //<<<<<<<<<< Added to force an open after the copy - not essential
}
@Override
public void onCreate(SQLiteDatabase db) {
//createDataBase(); <<<<<<<<<< relying on this was the cause of the issue >>>>>>>>>>
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
//<<<<<<<<<< NOT NEEDED AND SHOULD NOT BE CALLED >>>>>>>>>
private void createDataBase() {
boolean dbExist = checkDataBase();
if (!dbExist) {
copyDataBase();
}
}
private boolean checkDataBase() {
System.out.println("DB_PATH : " + DB_PATH);
File dbFile = new File(DB_PATH);
if (dbFile.exists()) return true;
//<<<<<<<<<< ADDED to create the databases directory if it doesn't exist >>>>>>>>>>
//it may be that getWritableDatabase was used to circumvent the issue that the copy would fail in the databases directory does not exist, hence this fix is included
if (!new File(dbFile.getParent()).exists()) {
new File(dbFile.getParent()).mkdirs();
}
return false;
}
private void copyDataBase() {
Log.i("Database",
"New database is being copied to device!");
byte[] buffer = new byte[1024];
//<<<<<<<<<< ADDED to delete wal and shm files if they exist (3rd fix) >>>>>>>>>>
File dbDirectory = new File(new File(DB_PATH).getParent());
File dbwal = new File(dbDirectory.getPath() + File.separator + DB_NAME + "-wal");
if (dbwal.exists()) {
dbwal.delete();
}
File dbshm = new File(dbDirectory.getPath() + File.separator + DB_NAME + "-shm");
if (dbshm.exists()) {
dbshm.delete();
}
//<<<<<<<<<< END OF ADDED CODE >>>>>>>>>>
OutputStream myOutput;
int length;
InputStream myInput;
try {
myInput = context.getAssets().open(DB_NAME);
myOutput = new FileOutputStream(DB_PATH);
while ((length = myInput.read(buffer)) > 0) {
myOutput.write(buffer, 0, length);
}
myOutput.close();
myOutput.flush();
myInput.close();
Log.i("Database",
"New database has been copied to device!");
} catch (IOException e) {
e.printStackTrace();
}
}
}
这已在Android 5和Android 10上使用活动中的以下代码进行了测试(以及用于转储模式的其他代码(请注意，不是您的数据库而是可用的数据库)):-
This has been tested on both Android 5 and Android 10 using the following code from an activity (along with additional code to dump the schema (note obviously NOT your database rather one that was available )):-
DBHelper mDBHlpr;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mDBHlpr = new DBHelper(this);
根据日志的结果:-
2019-05-07 06:20:53.148 I/System.out: DB_PATH : /data/user/0/soa.usingyourownsqlitedatabaseblog/databases/myDBName
2019-05-07 06:20:53.148 I/Database: New database is being copied to device!
2019-05-07 06:20:53.149 I/Database: New database has been copied to device!
2019-05-07 06:20:53.168 I/System.out: >>>>> Dumping cursor android.database.sqlite.SQLiteCursor@e3fe34f
2019-05-07 06:20:53.169 I/System.out: 0 {
2019-05-07 06:20:53.169 I/System.out: type=table
2019-05-07 06:20:53.169 I/System.out: name=Categories
2019-05-07 06:20:53.169 I/System.out: tbl_name=Categories
2019-05-07 06:20:53.169 I/System.out: rootpage=2
2019-05-07 06:20:53.169 I/System.out: sql=CREATE TABLE "Categories" (
2019-05-07 06:20:53.169 I/System.out: "not_id" integer NOT NULL,
2019-05-07 06:20:53.169 I/System.out: "CategoryLabel" TEXT,
2019-05-07 06:20:53.169 I/System.out: "Colour" integer,
2019-05-07 06:20:53.169 I/System.out: PRIMARY KEY ("not_id")
2019-05-07 06:20:53.169 I/System.out: )
2019-05-07 06:20:53.170 I/System.out: }
2019-05-07 06:20:53.170 I/System.out: 1 {
2019-05-07 06:20:53.170 I/System.out: type=table
2019-05-07 06:20:53.170 I/System.out: name=Content
2019-05-07 06:20:53.170 I/System.out: tbl_name=Content
2019-05-07 06:20:53.170 I/System.out: rootpage=3
2019-05-07 06:20:53.170 I/System.out: sql=CREATE TABLE "Content" (
2019-05-07 06:20:53.170 I/System.out: "again_not_id" INTEGER NOT NULL,
2019-05-07 06:20:53.170 I/System.out: "Text" TEXT,
2019-05-07 06:20:53.170 I/System.out: "Source" VARCHAR,
2019-05-07 06:20:53.170 I/System.out: "Category" integer,
2019-05-07 06:20:53.170 I/System.out: "VerseOrder" integer,
2019-05-07 06:20:53.170 I/System.out: PRIMARY KEY ("again_not_id")
2019-05-07 06:20:53.170 I/System.out: )
2019-05-07 06:20:53.170 I/System.out: }
2019-05-07 06:20:53.171 I/System.out: 2 {
2019-05-07 06:20:53.171 I/System.out: type=table
2019-05-07 06:20:53.171 I/System.out: name=android_metadata
2019-05-07 06:20:53.171 I/System.out: tbl_name=android_metadata
2019-05-07 06:20:53.171 I/System.out: rootpage=4
2019-05-07 06:20:53.171 I/System.out: sql=CREATE TABLE android_metadata (locale TEXT)
2019-05-07 06:20:53.171 I/System.out: }
2019-05-07 06:20:53.171 I/System.out: <<<<<
这篇关于使用预先填充的数据库运送android应用的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！