在 sqlite 中输入的数据在 android pie 中的应用重启时自动删除
Data entered in sqlite gets deleted automatically on app restart in android pie
SQLite 数据在 android pie.App 中重新启动应用程序后消失，在其他版本上工作正常，但在 android pie 中，当您重新启动应用程序时，最后几个条目不是 visible.Database 并不像其他条目显示的那样完全为空。
我尝试通过禁用 WriteAheadLogging 将 WAL 模式设置为 false，这似乎在某些设备上有效，但问题并未完全解决，因为某些设备仍在报告问题，因此我尝试将 PRAGMA 日志模式设置为 TRUNCATE，但这也确实如此不工作。
public myDbHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onConfigure(SQLiteDatabase db) {
super.onConfigure(db);
db.disableWriteAheadLogging();
Cursor c1=db.rawQuery("PRAGMA journal_mode=TRUNCATE",null);
c1.close();
}
public static synchronized myDbHelper getInstance(Context context) {
if (mInstance == null) {
mInstance = new myDbHelper(context.getApplicationContext());
mInstance.setWriteAheadLoggingEnabled(false);
}
return mInstance;
}
然后在我的片段中：
myDbHelper dbHelper = myDbHelper.getInstance(getActivity());
我没有收到任何错误消息，只是最后几个条目没有显示，就好像它们没有保存在 database.Any 帮助中非常感谢。
我不认为这个问题直接是由于 WAL 模式是否打开，而是您可能没有正确确定最后几个条目.
编码mInstance.setWriteAheadLoggingEnabled(false);会在onConfigure本身被调用之前直接关闭WAL（见下文）
我要做的第一件事就是改变
public myDbHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
至：-
private myDbHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
确保您不会无意中获得 rouge myDBHelper.
实例
作为临时措施，您可能还希望将以下方法添加到您的 myDBHeleper class :-
public void logMode(SQLiteDatabase db, String tagextra, String dbname, Context context) {
Log.d("BUILD","Build is " + Build.VERSION.SDK_INT);
File dbf = new File(context.getDatabasePath(dbname).toString());
File dbfwal = new File(dbf.getPath() + "-wal");
File dbfshm = new File(dbf.getPath() + "-shm");
if (dbfwal.exists()) {
Log.d("-WALCHK " + tagextra,"The -wal file was found an is " + String.valueOf(dbfwal.length()));
} else {
Log.d("-WALCHK " + tagextra,"The -wal file doesn't exist.");
}
if (dbfshm.exists()) {
Log.d("-SHMCHK " + tagextra,"The -shm file was found an is " + String.valueOf(dbfwal.length()));
} else {
Log.d("-SHMCHK " + tagextra,"The -shm file doesn't exist");
}
if (db == null) {
db = this.getWritableDatabase();
}
Cursor csr = db.rawQuery("PRAGMA journal_mode",null);
if (csr.moveToFirst()) {
Log.d("LOGMODE " + tagextra ,"Database mode is " + csr.getString(0));
}
}
这可以用来确定模式以及 -wal 和 -shm 文件是否存在以及是否有任何数据。
简而言之，它可以用来消除任何关于问题是由 WAL 模式引起的担忧。
例如使用下面的近似你的myDatabaseHelperclass。但是除了你的代码：-
- 上述 logMode 方法的调用已包含在相关点。
- 已包含 onCreateMethod 以创建 table 并添加初始行。
- 构造函数已设为 私有
所以它看起来像:-
public class myDbHelper extends SQLiteOpenHelper {
public static final String DATABASE_NAME = "mydb";
public static final int DATABASE_VERSION = 1;
public static final String TBL_USER = "user";
public static final String COL_USER_ID = BaseColumns._ID;
public static final String COl_USER_NAME = "_name";
public static final String COL_USER_EMAIL = "_email";
public static final String COl_USER_PASSWORD = "_password";
private static myDbHelper mInstance;
private Context mContext;
private myDbHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
mContext = context;
logMode(this.getWritableDatabase(),"CONSTRUCT",DATABASE_NAME,context); // Note will force an open
}
@Override
public void onConfigure(SQLiteDatabase db) {
logMode(db, "ONCONFIG1", DATABASE_NAME,mContext);
super.onConfigure(db);
db.disableWriteAheadLogging();
logMode(db,"ONCONFIG2",DATABASE_NAME,mContext);
Cursor c1=db.rawQuery("PRAGMA journal_mode=TRUNCATE",null);
c1.close();
logMode(db,"ONCONFIG3",DATABASE_NAME,mContext);
}
public static synchronized myDbHelper getInstance(Context context) {
if (mInstance == null) {
mInstance = new myDbHelper(context.getApplicationContext());
mInstance.setWriteAheadLoggingEnabled(false);
}
mInstance.logMode(mInstance.getWritableDatabase(),"INSTANCE",mInstance.getDatabaseName(),context );
return mInstance;
}
@Override
public void onCreate(SQLiteDatabase db) {
logMode(db,"ONCREATE1",DATABASE_NAME,mContext);
db.execSQL("CREATE TABLE IF NOT EXISTS " + TBL_USER +
"(" +
COL_USER_ID + " INTEGER PRIMARY KEY," +
COl_USER_NAME + " TEXT UNIQUE," +
COL_USER_EMAIL + " TEXT," +
COl_USER_PASSWORD + " TEXT" +
")");
//Add a row when oncreate is called
db.execSQL("INSERT INTO " + TBL_USER + " (" +
COl_USER_NAME + "," +
COL_USER_EMAIL + "," +
COl_USER_PASSWORD +
") VALUES('testuser','testuser@mail.com','1234567890')");
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
public long addUser(String name, String email, String passowrd) {
ContentValues cv = new ContentValues();
cv.put(COl_USER_NAME,name);
cv.put(COL_USER_EMAIL,email);
cv.put(COl_USER_PASSWORD,passowrd);
SQLiteDatabase db = this.getWritableDatabase();
logMode(db,"ADDUSER1",DATABASE_NAME,mContext);
return db.insert(TBL_USER,null,cv);
}
public void logMode(SQLiteDatabase db, String tagextra, String dbname, Context context) {
Log.d("BUILD","Build is " + Build.VERSION.SDK_INT);
File dbf = new File(context.getDatabasePath(dbname).toString());
File dbfwal = new File(dbf.getPath() + "-wal");
File dbfshm = new File(dbf.getPath() + "-shm");
if (dbfwal.exists()) {
Log.d("-WALCHK " + tagextra,"The -wal file was found an is " + String.valueOf(dbfwal.length()));
} else {
Log.d("-WALCHK " + tagextra,"The -wal file doesn't exist.");
}
if (dbfshm.exists()) {
Log.d("-SHMCHK " + tagextra,"The -shm file was found an is " + String.valueOf(dbfwal.length()));
} else {
Log.d("-SHMCHK " + tagextra,"The -shm file doesn't exist");
}
if (db == null) {
db = this.getWritableDatabase();
}
Cursor csr = db.rawQuery("PRAGMA journal_mode",null);
if (csr.moveToFirst()) {
Log.d("LOGMODE " + tagextra ,"Database mode is " + csr.getString(0));
}
}
}
下面是片段的onStart方法：-
@Override
public void onStart() {
super.onStart();
myDbHelper dbHelper = myDbHelper.getInstance(getActivity());
dbHelper.logMode(dbHelper.getWritableDatabase(),"FRGONSTRT1",myDbHelper.DATABASE_NAME,getActivity());
dbHelper.addUser("Fred","fred@fredmail.com","password");
Cursor csr = dbHelper.getReadableDatabase().query(myDbHelper.TBL_USER,null,null,null,null,null,null);
DatabaseUtils.dumpCursor(csr);
csr.close();
}
就是这样:-
- 获取一个 myDBHelper 实例。
- 调用 logMode 方法。
- 添加一行。
- 将所有数据提取到 Cursor 中并转储 Cursor。
测试
测试 1
在具有 API 28 和 运行 的 Android（模拟器）上卸载应用程序会导致：-
2019-07-07 10:38:56.022 D/BUILD: Build is 28
2019-07-07 10:38:56.022 D/-WALCHK ONCONFIG1: The -wal file was found an is 16512
2019-07-07 10:38:56.022 D/-SHMCHK ONCONFIG1: The -shm file was found an is 16512
2019-07-07 10:38:56.023 D/LOGMODE ONCONFIG1: Database mode is wal
2019-07-07 10:38:56.038 D/BUILD: Build is 28
2019-07-07 10:38:56.038 D/-WALCHK ONCONFIG2: The -wal file doesn't exist.
2019-07-07 10:38:56.038 D/-SHMCHK ONCONFIG2: The -shm file doesn't exist
2019-07-07 10:38:56.039 D/LOGMODE ONCONFIG2: Database mode is truncate
2019-07-07 10:38:56.039 D/BUILD: Build is 28
2019-07-07 10:38:56.039 D/-WALCHK ONCONFIG3: The -wal file doesn't exist.
2019-07-07 10:38:56.039 D/-SHMCHK ONCONFIG3: The -shm file doesn't exist
2019-07-07 10:38:56.040 D/LOGMODE ONCONFIG3: Database mode is truncate
2019-07-07 10:38:56.041 D/BUILD: Build is 28
2019-07-07 10:38:56.042 D/-WALCHK ONCREATE1: The -wal file doesn't exist.
2019-07-07 10:38:56.043 D/-SHMCHK ONCREATE1: The -shm file doesn't exist
2019-07-07 10:38:56.043 D/LOGMODE ONCREATE1: Database mode is truncate
2019-07-07 10:38:56.054 D/BUILD: Build is 28
2019-07-07 10:38:56.054 D/-WALCHK CONSTRUCT: The -wal file doesn't exist.
2019-07-07 10:38:56.055 D/-SHMCHK CONSTRUCT: The -shm file doesn't exist
2019-07-07 10:38:56.055 D/LOGMODE CONSTRUCT: Database mode is truncate
2019-07-07 10:38:56.056 D/BUILD: Build is 28
2019-07-07 10:38:56.057 D/-WALCHK INSTANCE: The -wal file doesn't exist.
2019-07-07 10:38:56.057 D/-SHMCHK INSTANCE: The -shm file doesn't exist
2019-07-07 10:38:56.058 D/LOGMODE INSTANCE: Database mode is truncate
2019-07-07 10:38:56.058 D/BUILD: Build is 28
2019-07-07 10:38:56.058 D/-WALCHK FRGONSTRT1: The -wal file doesn't exist.
2019-07-07 10:38:56.058 D/-SHMCHK FRGONSTRT1: The -shm file doesn't exist
2019-07-07 10:38:56.059 D/LOGMODE FRGONSTRT1: Database mode is truncate
2019-07-07 10:38:56.059 D/BUILD: Build is 28
2019-07-07 10:38:56.059 D/-WALCHK ADDUSER1: The -wal file doesn't exist.
2019-07-07 10:38:56.059 D/-SHMCHK ADDUSER1: The -shm file doesn't exist
2019-07-07 10:38:56.060 D/LOGMODE ADDUSER1: Database mode is truncate
2019-07-07 10:38:56.069 I/System.out: >>>>> Dumping cursor android.database.sqlite.SQLiteCursor@4f533b6
2019-07-07 10:38:56.070 I/System.out: 0 {
2019-07-07 10:38:56.070 I/System.out: _id=1
2019-07-07 10:38:56.070 I/System.out: _name=testuser
2019-07-07 10:38:56.070 I/System.out: _email=testuser@mail.com
2019-07-07 10:38:56.070 I/System.out: _password=1234567890
2019-07-07 10:38:56.070 I/System.out: }
2019-07-07 10:38:56.070 I/System.out: 1 {
2019-07-07 10:38:56.070 I/System.out: _id=2
2019-07-07 10:38:56.070 I/System.out: _name=Fred
2019-07-07 10:38:56.070 I/System.out: _email=fred@fredmail.com
2019-07-07 10:38:56.070 I/System.out: _password=password
2019-07-07 10:38:56.070 I/System.out: }
2019-07-07 10:38:56.070 I/System.out: <<<<<
在这种情况下，由于线路
logMode(this.getWritableDatabase(),"CONSTRUCT",DATABASE_NAME,context); // Note will force an open
之前被调用
mInstance.setWriteAheadLoggingEnabled(false);
数据库最初处于 WAL 模式，但 onConfigure 方法中的行 db.disableWriteAheadLogging(); 将模式更改为截断并在这样做时提交事务（-wal 中有未完成的事务 文件，因为它的大小大于 0，（-shm 基本上是 -wal 文件的副本））根据 :-
2019-07-07 10:38:56.022 D/-WALCHK ONCONFIG1: The -wal file was found an is 16512
事务已提交，因为在所有后续输出中 -wal 文件已被删除。
测试 2
应用程序重新运行（即现在使用现有数据）输出为：-
2019-07-07 10:52:11.722 I/InstantRun: starting instant run server: is main process
2019-07-07 10:52:11.812 D/BUILD: Build is 28
2019-07-07 10:52:11.812 D/-WALCHK ONCONFIG1: The -wal file was found an is 0
2019-07-07 10:52:11.812 D/-SHMCHK ONCONFIG1: The -shm file was found an is 0
2019-07-07 10:52:11.813 D/LOGMODE ONCONFIG1: Database mode is wal
........... subsequent output the same as first bar times
虽然数据库最初是在 WAL 中，但没有未完成的事务（唯一的区别）。
测试 3
如果注释掉行 logMode(this.getWritableDatabase(),"CONSTRUCT",DATABASE_NAME,context); // Note will force an open 并且应用程序被卸载并重新运行：-
2019-07-07 10:56:23.314 I/InstantRun: starting instant run server: is main process
2019-07-07 10:56:23.437 D/BUILD: Build is 28
2019-07-07 10:56:23.438 D/-WALCHK ONCONFIG1: The -wal file doesn't exist.
2019-07-07 10:56:23.438 D/-SHMCHK ONCONFIG1: The -shm file doesn't exist
2019-07-07 10:56:23.439 D/LOGMODE ONCONFIG1: Database mode is truncate
........... subsequent output the same as first bar times
然后第一次使用 （因为在调用 db.disableWriteAheadLogging(); 之前不强制打开） 导致数据库处于 TRUNCATE 模式。
SQLite 数据在 android pie.App 中重新启动应用程序后消失，在其他版本上工作正常，但在 android pie 中，当您重新启动应用程序时，最后几个条目不是 visible.Database 并不像其他条目显示的那样完全为空。
我尝试通过禁用 WriteAheadLogging 将 WAL 模式设置为 false，这似乎在某些设备上有效，但问题并未完全解决，因为某些设备仍在报告问题，因此我尝试将 PRAGMA 日志模式设置为 TRUNCATE，但这也确实如此不工作。
public myDbHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onConfigure(SQLiteDatabase db) {
super.onConfigure(db);
db.disableWriteAheadLogging();
Cursor c1=db.rawQuery("PRAGMA journal_mode=TRUNCATE",null);
c1.close();
}
public static synchronized myDbHelper getInstance(Context context) {
if (mInstance == null) {
mInstance = new myDbHelper(context.getApplicationContext());
mInstance.setWriteAheadLoggingEnabled(false);
}
return mInstance;
}
然后在我的片段中： myDbHelper dbHelper = myDbHelper.getInstance(getActivity());
我没有收到任何错误消息，只是最后几个条目没有显示，就好像它们没有保存在 database.Any 帮助中非常感谢。
我不认为这个问题直接是由于 WAL 模式是否打开，而是您可能没有正确确定最后几个条目.
编码mInstance.setWriteAheadLoggingEnabled(false);会在onConfigure本身被调用之前直接关闭WAL（见下文）
我要做的第一件事就是改变
public myDbHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
至：-
private myDbHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
确保您不会无意中获得 rouge myDBHelper.
实例作为临时措施，您可能还希望将以下方法添加到您的 myDBHeleper class :-
public void logMode(SQLiteDatabase db, String tagextra, String dbname, Context context) {
Log.d("BUILD","Build is " + Build.VERSION.SDK_INT);
File dbf = new File(context.getDatabasePath(dbname).toString());
File dbfwal = new File(dbf.getPath() + "-wal");
File dbfshm = new File(dbf.getPath() + "-shm");
if (dbfwal.exists()) {
Log.d("-WALCHK " + tagextra,"The -wal file was found an is " + String.valueOf(dbfwal.length()));
} else {
Log.d("-WALCHK " + tagextra,"The -wal file doesn't exist.");
}
if (dbfshm.exists()) {
Log.d("-SHMCHK " + tagextra,"The -shm file was found an is " + String.valueOf(dbfwal.length()));
} else {
Log.d("-SHMCHK " + tagextra,"The -shm file doesn't exist");
}
if (db == null) {
db = this.getWritableDatabase();
}
Cursor csr = db.rawQuery("PRAGMA journal_mode",null);
if (csr.moveToFirst()) {
Log.d("LOGMODE " + tagextra ,"Database mode is " + csr.getString(0));
}
}
这可以用来确定模式以及 -wal 和 -shm 文件是否存在以及是否有任何数据。
简而言之，它可以用来消除任何关于问题是由 WAL 模式引起的担忧。
例如使用下面的近似你的myDatabaseHelperclass。但是除了你的代码：-
- 上述 logMode 方法的调用已包含在相关点。
- 已包含 onCreateMethod 以创建 table 并添加初始行。
- 构造函数已设为 私有
所以它看起来像:-
public class myDbHelper extends SQLiteOpenHelper {
public static final String DATABASE_NAME = "mydb";
public static final int DATABASE_VERSION = 1;
public static final String TBL_USER = "user";
public static final String COL_USER_ID = BaseColumns._ID;
public static final String COl_USER_NAME = "_name";
public static final String COL_USER_EMAIL = "_email";
public static final String COl_USER_PASSWORD = "_password";
private static myDbHelper mInstance;
private Context mContext;
private myDbHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
mContext = context;
logMode(this.getWritableDatabase(),"CONSTRUCT",DATABASE_NAME,context); // Note will force an open
}
@Override
public void onConfigure(SQLiteDatabase db) {
logMode(db, "ONCONFIG1", DATABASE_NAME,mContext);
super.onConfigure(db);
db.disableWriteAheadLogging();
logMode(db,"ONCONFIG2",DATABASE_NAME,mContext);
Cursor c1=db.rawQuery("PRAGMA journal_mode=TRUNCATE",null);
c1.close();
logMode(db,"ONCONFIG3",DATABASE_NAME,mContext);
}
public static synchronized myDbHelper getInstance(Context context) {
if (mInstance == null) {
mInstance = new myDbHelper(context.getApplicationContext());
mInstance.setWriteAheadLoggingEnabled(false);
}
mInstance.logMode(mInstance.getWritableDatabase(),"INSTANCE",mInstance.getDatabaseName(),context );
return mInstance;
}
@Override
public void onCreate(SQLiteDatabase db) {
logMode(db,"ONCREATE1",DATABASE_NAME,mContext);
db.execSQL("CREATE TABLE IF NOT EXISTS " + TBL_USER +
"(" +
COL_USER_ID + " INTEGER PRIMARY KEY," +
COl_USER_NAME + " TEXT UNIQUE," +
COL_USER_EMAIL + " TEXT," +
COl_USER_PASSWORD + " TEXT" +
")");
//Add a row when oncreate is called
db.execSQL("INSERT INTO " + TBL_USER + " (" +
COl_USER_NAME + "," +
COL_USER_EMAIL + "," +
COl_USER_PASSWORD +
") VALUES('testuser','testuser@mail.com','1234567890')");
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
public long addUser(String name, String email, String passowrd) {
ContentValues cv = new ContentValues();
cv.put(COl_USER_NAME,name);
cv.put(COL_USER_EMAIL,email);
cv.put(COl_USER_PASSWORD,passowrd);
SQLiteDatabase db = this.getWritableDatabase();
logMode(db,"ADDUSER1",DATABASE_NAME,mContext);
return db.insert(TBL_USER,null,cv);
}
public void logMode(SQLiteDatabase db, String tagextra, String dbname, Context context) {
Log.d("BUILD","Build is " + Build.VERSION.SDK_INT);
File dbf = new File(context.getDatabasePath(dbname).toString());
File dbfwal = new File(dbf.getPath() + "-wal");
File dbfshm = new File(dbf.getPath() + "-shm");
if (dbfwal.exists()) {
Log.d("-WALCHK " + tagextra,"The -wal file was found an is " + String.valueOf(dbfwal.length()));
} else {
Log.d("-WALCHK " + tagextra,"The -wal file doesn't exist.");
}
if (dbfshm.exists()) {
Log.d("-SHMCHK " + tagextra,"The -shm file was found an is " + String.valueOf(dbfwal.length()));
} else {
Log.d("-SHMCHK " + tagextra,"The -shm file doesn't exist");
}
if (db == null) {
db = this.getWritableDatabase();
}
Cursor csr = db.rawQuery("PRAGMA journal_mode",null);
if (csr.moveToFirst()) {
Log.d("LOGMODE " + tagextra ,"Database mode is " + csr.getString(0));
}
}
}
下面是片段的onStart方法：-
@Override
public void onStart() {
super.onStart();
myDbHelper dbHelper = myDbHelper.getInstance(getActivity());
dbHelper.logMode(dbHelper.getWritableDatabase(),"FRGONSTRT1",myDbHelper.DATABASE_NAME,getActivity());
dbHelper.addUser("Fred","fred@fredmail.com","password");
Cursor csr = dbHelper.getReadableDatabase().query(myDbHelper.TBL_USER,null,null,null,null,null,null);
DatabaseUtils.dumpCursor(csr);
csr.close();
}
就是这样:-
- 获取一个 myDBHelper 实例。
- 调用 logMode 方法。
- 添加一行。
- 将所有数据提取到 Cursor 中并转储 Cursor。
测试
测试 1
在具有 API 28 和 运行 的 Android（模拟器）上卸载应用程序会导致：-
2019-07-07 10:38:56.022 D/BUILD: Build is 28
2019-07-07 10:38:56.022 D/-WALCHK ONCONFIG1: The -wal file was found an is 16512
2019-07-07 10:38:56.022 D/-SHMCHK ONCONFIG1: The -shm file was found an is 16512
2019-07-07 10:38:56.023 D/LOGMODE ONCONFIG1: Database mode is wal
2019-07-07 10:38:56.038 D/BUILD: Build is 28
2019-07-07 10:38:56.038 D/-WALCHK ONCONFIG2: The -wal file doesn't exist.
2019-07-07 10:38:56.038 D/-SHMCHK ONCONFIG2: The -shm file doesn't exist
2019-07-07 10:38:56.039 D/LOGMODE ONCONFIG2: Database mode is truncate
2019-07-07 10:38:56.039 D/BUILD: Build is 28
2019-07-07 10:38:56.039 D/-WALCHK ONCONFIG3: The -wal file doesn't exist.
2019-07-07 10:38:56.039 D/-SHMCHK ONCONFIG3: The -shm file doesn't exist
2019-07-07 10:38:56.040 D/LOGMODE ONCONFIG3: Database mode is truncate
2019-07-07 10:38:56.041 D/BUILD: Build is 28
2019-07-07 10:38:56.042 D/-WALCHK ONCREATE1: The -wal file doesn't exist.
2019-07-07 10:38:56.043 D/-SHMCHK ONCREATE1: The -shm file doesn't exist
2019-07-07 10:38:56.043 D/LOGMODE ONCREATE1: Database mode is truncate
2019-07-07 10:38:56.054 D/BUILD: Build is 28
2019-07-07 10:38:56.054 D/-WALCHK CONSTRUCT: The -wal file doesn't exist.
2019-07-07 10:38:56.055 D/-SHMCHK CONSTRUCT: The -shm file doesn't exist
2019-07-07 10:38:56.055 D/LOGMODE CONSTRUCT: Database mode is truncate
2019-07-07 10:38:56.056 D/BUILD: Build is 28
2019-07-07 10:38:56.057 D/-WALCHK INSTANCE: The -wal file doesn't exist.
2019-07-07 10:38:56.057 D/-SHMCHK INSTANCE: The -shm file doesn't exist
2019-07-07 10:38:56.058 D/LOGMODE INSTANCE: Database mode is truncate
2019-07-07 10:38:56.058 D/BUILD: Build is 28
2019-07-07 10:38:56.058 D/-WALCHK FRGONSTRT1: The -wal file doesn't exist.
2019-07-07 10:38:56.058 D/-SHMCHK FRGONSTRT1: The -shm file doesn't exist
2019-07-07 10:38:56.059 D/LOGMODE FRGONSTRT1: Database mode is truncate
2019-07-07 10:38:56.059 D/BUILD: Build is 28
2019-07-07 10:38:56.059 D/-WALCHK ADDUSER1: The -wal file doesn't exist.
2019-07-07 10:38:56.059 D/-SHMCHK ADDUSER1: The -shm file doesn't exist
2019-07-07 10:38:56.060 D/LOGMODE ADDUSER1: Database mode is truncate
2019-07-07 10:38:56.069 I/System.out: >>>>> Dumping cursor android.database.sqlite.SQLiteCursor@4f533b6
2019-07-07 10:38:56.070 I/System.out: 0 {
2019-07-07 10:38:56.070 I/System.out: _id=1
2019-07-07 10:38:56.070 I/System.out: _name=testuser
2019-07-07 10:38:56.070 I/System.out: _email=testuser@mail.com
2019-07-07 10:38:56.070 I/System.out: _password=1234567890
2019-07-07 10:38:56.070 I/System.out: }
2019-07-07 10:38:56.070 I/System.out: 1 {
2019-07-07 10:38:56.070 I/System.out: _id=2
2019-07-07 10:38:56.070 I/System.out: _name=Fred
2019-07-07 10:38:56.070 I/System.out: _email=fred@fredmail.com
2019-07-07 10:38:56.070 I/System.out: _password=password
2019-07-07 10:38:56.070 I/System.out: }
2019-07-07 10:38:56.070 I/System.out: <<<<<
在这种情况下，由于线路
logMode(this.getWritableDatabase(),"CONSTRUCT",DATABASE_NAME,context); // Note will force an open
之前被调用
mInstance.setWriteAheadLoggingEnabled(false);
数据库最初处于 WAL 模式，但 onConfigure 方法中的行 db.disableWriteAheadLogging(); 将模式更改为截断并在这样做时提交事务（-wal 中有未完成的事务 文件，因为它的大小大于 0，（-shm 基本上是 -wal 文件的副本））根据 :-
2019-07-07 10:38:56.022 D/-WALCHK ONCONFIG1: The -wal file was found an is 16512
事务已提交，因为在所有后续输出中 -wal 文件已被删除。
测试 2
应用程序重新运行（即现在使用现有数据）输出为：-
2019-07-07 10:52:11.722 I/InstantRun: starting instant run server: is main process
2019-07-07 10:52:11.812 D/BUILD: Build is 28
2019-07-07 10:52:11.812 D/-WALCHK ONCONFIG1: The -wal file was found an is 0
2019-07-07 10:52:11.812 D/-SHMCHK ONCONFIG1: The -shm file was found an is 0
2019-07-07 10:52:11.813 D/LOGMODE ONCONFIG1: Database mode is wal
........... subsequent output the same as first bar times
虽然数据库最初是在 WAL 中，但没有未完成的事务（唯一的区别）。
测试 3
如果注释掉行 logMode(this.getWritableDatabase(),"CONSTRUCT",DATABASE_NAME,context); // Note will force an open 并且应用程序被卸载并重新运行：-
2019-07-07 10:56:23.314 I/InstantRun: starting instant run server: is main process
2019-07-07 10:56:23.437 D/BUILD: Build is 28
2019-07-07 10:56:23.438 D/-WALCHK ONCONFIG1: The -wal file doesn't exist.
2019-07-07 10:56:23.438 D/-SHMCHK ONCONFIG1: The -shm file doesn't exist
2019-07-07 10:56:23.439 D/LOGMODE ONCONFIG1: Database mode is truncate
........... subsequent output the same as first bar times
然后第一次使用 （因为在调用 db.disableWriteAheadLogging(); 之前不强制打开） 导致数据库处于 TRUNCATE 模式。