我在要手动放置的软件包数据库下的资产文件夹中有一个SQLite文件（例如：src-> main-> asset-> databases-> q-db（q-db是我的SQLite文件）。 / p>
现在，我想读取其版本号，如果要将此版本放置在我自己的应用程序中，则要进行匹配，如果不存在，则需要将其复制到我的数据库中，否则将跳过。当然，这是第一次从文件复制，而下次每次打开应用程序时，它将检查版本号。
我用Google搜索了很多，但是无法获取文件的版本号，我得到的是我不想使用的SQLite版本号。非常感谢您的支持。
供参考：我正在关注与此类似的人
答案 0 :(得分：0)
没有单个版本号，而是版本号可以是多个值。
猜测您正在与Android SDK SQLiteOpenHelper使用的 user_version 相邻。
还有 application_id ，它可以像user_version一样用作用户变量。
您已经遇到了SQLite_Version，因此可以打折。
还有data_version，它不太可能是版本号，因为它旨在指示数据库文件是否已实时修改。
也有schema_version，您可能不希望将其用作 警告：滥用此编译指示可能会导致数据库损坏。
如前所述，您可能正在谈论 user_version 。首先要注意的是，它是一个用户控制的变量/字段，可自定义使用。 SQlite不会使用或更改 user_version ，但允许对其进行更改和使用。
此外，SQLite管理器（例如DB Browser，Navicat等）不会自动更改版本号。因此，在将数据库文件复制到Assets文件夹之前，您必须故意更改user_version使其可用（请注意，如果这样做，并且您正在使用SQLiteOpenHelper的子类，则onUpgrade并且可以调用onDowngrade方法。
如果未专门更改user_version并且仅通过SQLite Manager工具访问该数据库，则它的user_version将为0。如果通过从使用SQLiteOpenHelper子类的Android应用程序复制数据库文件来打开数据库文件，则它的user_version将为1或更大（取决于最后一个值用作SQLiteOpenHelper的构造函数的第4个参数）。当然，如果以编程方式更改了user_version，则如果将文件复制到SQlite Manager工具中，也会反映出这种变化。
在复制文件之前，通常会在SQlite Manager工具中将user_version更改为适当的值。
您可以使用SQL PRAGMA user_version = 5;更改 user_version
您可以使用PRAGMA user_version或SELECT * FROM pragma_user_version;
如果需要在打开数据库之前检查版本，则可以读取偏移量60处的4个字节并将4个字节转换为整数，以对照另一个值检查user_version。否则，您可能必须从assets文件夹复制文件（可能使用不同的名称），将其作为SQLiteDatabase打开，并使用上述SQL检索user_version，然后对照其他值进行检查，以关闭数据库文件。不需要时删除文件，否则删除先前的数据库文件，然后重命名复制的文件。
以下是一个有效的示例（请注意，我很少使用Kotlin，并且已使用Java的AS Studio对其进行了转换。）
这使用了一个类，即 SQLAssetVersionCheck ，该类从文件中提取版本号，而不是将文件作为SQLiteDatabase打开。
class SQLAssetVersionCheck
/**
* Full SQLAssetVersionCheck Constructor - sub directories can be specified
* @param context Assets are part of package so use the context to get the asset file
* @param dbName The database name (i.e. the file name)
* @param subDirectories The sub-directories as per the heirarchial order
* @param dbVersion The database version to check against
*/
(context: Context, val databaseName: String, subDirectories: Array<String>?, dbVersion: Int) {
val assetPath: String
var databaseVersion: Int = 0
private set
var result: Int = 0
private set
init {
assetPath = applySubDirectories(databaseName, subDirectories)
Log.d("SQLAVC", "Looking for Asset $assetPath")
var stage = 0
try {
val `is` = context.assets.open(assetPath)
stage++
// Get the first 64 bytes of the header
val v = ByteArray(64)
`is`.read(v, 0, 64)
// only interested in the 4 bytes from offset 60 so get them
val v2 = ByteArray(4)
for (i in 60..63) {
v2[i - 60] = v[i]
}
stage++
// Done with the InputStream so close it
`is`.close()
// Extarct the stored DBVersion
databaseVersion = ByteBuffer.wrap(v2).int
if (databaseVersion < dbVersion) {
result = ASSETVERSIONLOW
}
if (databaseVersion > dbVersion) {
result = ASSETVERSIONHIGH
}
if (databaseVersion == dbVersion) {
result = ASSETVERSIONMATCH
}
} catch (e: IOException) {
e.printStackTrace()
when (stage) {
0 -> result = ASSETNOTFOUND
1 -> result = ASSETIOERROR
}
}
}
constructor(context: Context, dbName: String, dbVersion: Int) : this(context, dbName, null, dbVersion) {}
private fun applySubDirectories(dbname: String, subDirectories: Array<String>?): String {
val base = StringBuffer("")
var firstdirectory = true
if (subDirectories != null) {
for (d in subDirectories) {
if (!firstdirectory) {
base.append(File.separatorChar)
}
firstdirectory = false
base.append(d)
}
}
if (base.length > 0) {
base.append(File.separatorChar)
}
base.append(dbname)
return base.toString()
}
companion object {
val ASSETNOTFOUND = -2
val ASSETIOERROR = -3
val ASSETVERSIONMATCH = 0
val ASSETVERSIONHIGH = 1
val ASSETVERSIONLOW = -1
}
}
这是一个Activity，它使用上述类两次来尝试检查 testdb 文件中的版本。
第一次使用时未在 assets 文件夹（不是数据库子目录）中找到数据库文件 testdb 。
第二种用法是找到 testdb 文件，因为指定了子目录 databases （完整构造函数的第3个参数），在资产/数据库/ 文件夹，即资产/数据库/ testdb ：-
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val db_version_to_check_against = 100
var mAVC1 = SQLAssetVersionCheck(this, "testdb", 100)
var result = ""
when (mAVC1.result) {
SQLAssetVersionCheck.ASSETIOERROR -> result = "IO ERROR detected - check the Log"
SQLAssetVersionCheck.ASSETNOTFOUND -> result = "The Asset, for Database " + mAVC1.databaseName + " was not located at " + mAVC1.assetPath
SQLAssetVersionCheck.ASSETVERSIONHIGH -> result = "The Asset was located and the version number being " +
mAVC1.databaseVersion.toString() +
" was higher than the version to be checked which was " +
db_version_to_check_against.toString()
SQLAssetVersionCheck.ASSETVERSIONLOW -> result = "The Asset was located and the version number being " +
mAVC1.databaseVersion.toString() +
" was lower than the version to be checked which was " +
db_version_to_check_against.toString()
SQLAssetVersionCheck.ASSETVERSIONMATCH -> result = "The Asset version and the version to be check ed are the same."
}
Log.d("ASSETVERSIONCHECK", "The result of the version check was - $result")
var mAVC2 = SQLAssetVersionCheck(this, "testdb", arrayOf("databases"), db_version_to_check_against)
result = ""
when (mAVC2.result) {
SQLAssetVersionCheck.ASSETIOERROR -> result = "IO ERROR detected - check the Log"
SQLAssetVersionCheck.ASSETNOTFOUND -> result = "The Asset, for Database " + mAVC2.databaseName + " was not located at " + mAVC2.assetPath
SQLAssetVersionCheck.ASSETVERSIONHIGH -> result = "The Asset was located and the version number being " +
mAVC2.databaseVersion.toString() +
" was higher than the version to be checked which was " +
db_version_to_check_against.toString()
SQLAssetVersionCheck.ASSETVERSIONLOW -> result = "The Asset was located and the version number being " +
mAVC2.databaseVersion.toString() +
" was lower than the version to be checked which was " +
db_version_to_check_against.toString()
SQLAssetVersionCheck.ASSETVERSIONMATCH -> result = "The Asset version and the version to be check ed are the same."
}
Log.d("ASSETVERSIONCHECK", "The result of the version check was - $result")
}
}
2019-02-19 13:11:34.473 19058-19058/com.example.so54741423assetdbversioning D/SQLAVC: Looking for Asset testdb
2019-02-19 13:11:34.473 19058-19058/com.example.so54741423assetdbversioning W/System.err: java.io.FileNotFoundException: testdb
2019-02-19 13:11:34.474 19058-19058/com.example.so54741423assetdbversioning W/System.err: at android.content.res.AssetManager.nativeOpenAsset(Native Method)
2019-02-19 13:11:34.474 19058-19058/com.example.so54741423assetdbversioning W/System.err: at android.content.res.AssetManager.open(AssetManager.java:744)
2019-02-19 13:11:34.474 19058-19058/com.example.so54741423assetdbversioning W/System.err: at android.content.res.AssetManager.open(AssetManager.java:721)
2019-02-19 13:11:34.474 19058-19058/com.example.so54741423assetdbversioning W/System.err: at com.example.so54741423assetdbversioning.SQLAssetVersionCheck.<init>(SQLAssetVersionCheck.kt:31)
2019-02-19 13:11:34.474 19058-19058/com.example.so54741423assetdbversioning W/System.err: at com.example.so54741423assetdbversioning.SQLAssetVersionCheck.<init>(SQLAssetVersionCheck.kt:67)
2019-02-19 13:11:34.474 19058-19058/com.example.so54741423assetdbversioning W/System.err: at com.example.so54741423assetdbversioning.MainActivity.onCreate(MainActivity.kt:17)
2019-02-19 13:11:34.474 19058-19058/com.example.so54741423assetdbversioning W/System.err: at android.app.Activity.performCreate(Activity.java:7136)
2019-02-19 13:11:34.475 19058-19058/com.example.so54741423assetdbversioning W/System.err: at android.app.Activity.performCreate(Activity.java:7127)
2019-02-19 13:11:34.475 19058-19058/com.example.so54741423assetdbversioning W/System.err: at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)
2019-02-19 13:11:34.475 19058-19058/com.example.so54741423assetdbversioning W/System.err: at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2893)
2019-02-19 13:11:34.475 19058-19058/com.example.so54741423assetdbversioning W/System.err: at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
2019-02-19 13:11:34.475 19058-19058/com.example.so54741423assetdbversioning W/System.err: at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
2019-02-19 13:11:34.475 19058-19058/com.example.so54741423assetdbversioning W/System.err: at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
2019-02-19 13:11:34.475 19058-19058/com.example.so54741423assetdbversioning W/System.err: at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
2019-02-19 13:11:34.475 19058-19058/com.example.so54741423assetdbversioning W/System.err: at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
2019-02-19 13:11:34.475 19058-19058/com.example.so54741423assetdbversioning W/System.err: at android.os.Handler.dispatchMessage(Handler.java:106)
2019-02-19 13:11:34.475 19058-19058/com.example.so54741423assetdbversioning W/System.err: at android.os.Looper.loop(Looper.java:193)
2019-02-19 13:11:34.476 19058-19058/com.example.so54741423assetdbversioning W/System.err: at android.app.ActivityThread.main(ActivityThread.java:6669)
2019-02-19 13:11:34.476 19058-19058/com.example.so54741423assetdbversioning W/System.err: at java.lang.reflect.Method.invoke(Native Method)
2019-02-19 13:11:34.476 19058-19058/com.example.so54741423assetdbversioning W/System.err: at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
2019-02-19 13:11:34.476 19058-19058/com.example.so54741423assetdbversioning W/System.err: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
2019-02-19 13:11:34.476 19058-19058/com.example.so54741423assetdbversioning D/ASSETVERSIONCHECK: The result of the version check was - The Asset, for Database testdb was not located at testdb
2019-02-19 13:11:34.476 19058-19058/com.example.so54741423assetdbversioning D/SQLAVC: Looking for Asset databases/testdb
2019-02-19 13:11:34.477 19058-19058/com.example.so54741423assetdbversioning D/ASSETVERSIONCHECK: The result of the version check was - The Asset was located and the version number being 5 was lower than the version to be checked which was 100
首次尝试找不到文件（显示捕获的异常），并显示行版本检查的结果是-数据库testdb的资产不在testdb上显示。
第二次尝试成功并导致版本检查的结果是-找到资产，并且版本号5低于要检查的版本100 < / p>
添加了空格行以将第二次尝试与第一次尝试分开。
使用SQLite Manager工具（Navicat）并使用：-
PRAGMA user_version = 101;
然后将文件（在Navicat中关闭连接后）复制到资产文件夹（所以我有两个testdb文件），那么结果是：-
2019-02-19 13:50:09.874 19253-19253/com.example.so54741423assetdbversioning D/SQLAVC: Looking for Asset testdb
2019-02-19 13:50:09.874 19253-19253/com.example.so54741423assetdbversioning D/ASSETVERSIONCHECK: The result of the version check was - The Asset was located and the version number being 101 was higher than the version to be checked which was 100
2019-02-19 13:50:09.874 19253-19253/com.example.so54741423assetdbversioning D/SQLAVC: Looking for Asset databases/testdb
2019-02-19 13:50:09.874 19253-19253/com.example.so54741423assetdbversioning D/ASSETVERSIONCHECK: The result of the version check was - The Asset was located and the version number being 5 was lower than the version to be checked which was 100