android - 使用预填充的数据库发布 android 应用程序
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,我什至得到了日志New database has been copied to device!
,但是当我尝试从 db 读取数据时,我遇到了no such table
异常。
注意:我正在尝试更新我的一个旧应用程序,相同的代码适用于 5.0 及以下的旧设备版本,但是当我尝试使用最新设备更新应用程序时,它不起作用。
解决方案
假设您复制到 assets 文件夹的数据库确实包含表,那么我相信您的问题是您正在实例化 DBHelper 的实例,然后您通过隐式或显式调用 getWritableDatabase 或getReadableDatabase 然后使用onCreate方法启动复制。
如果是这样,那么 get????ableDatabase 将创建一个空数据库,副本会覆盖它,但在以后的版本中,Android 9+,-shm 和 -wal 文件保持原样,然后打开数据库时,然后由于 -shm 和 -wal 文件与原始空数据库不匹配,因此检测到损坏,因此创建一个空的新数据库,因为 SDK 代码试图提供可用的数据库。
- 从 Android 9+ 开始,默认使用WAL(预写日志),这就是创建和使用 -shm 和 -wal 文件的原因。
有 3 个修复。
通过覆盖 SQLiteOpenHelper 类的 onConfigure 方法来使用disableWriteAheadLogging方法。然后使用较旧的日志模式。
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。
确保删除 -wal 和 -shm 文件(如果它们在复制时存在)。
使用第一个可能只是延迟不可避免的事情,并且不推荐使用,因为它没有利用 WAL 模式的好处。
您的 DBHelper 的以下版本包含第二个修复程序以及作为预防措施的第三个修复程序:-
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();
}
}
}
这已经在 Android 5 和 Android 10 上使用来自活动的以下代码进行了测试(以及用于转储模式的附加代码(注意显然不是您的数据库,而是可用的数据库)):-
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: <<<<<
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