如何从Android中放置在资产文件夹中的数据库文件中读取版本号

我在asset文件夹中的一个包databases下有一个SQLite文件，我手动将其放置如下：src->main->asset->databases->q-db q-db是我的SQLite文件

现在，我想读取它的版本号，并想匹配这个版本是否放在我自己的应用程序中，如果没有，则需要复制到我的数据库中，否则将跳过。当然，这是它第一次从文件中复制，下一次每当应用打开时，它都会检查版本号

我在谷歌上搜索了很多，但无法获得文件的版本号，我得到的是我的SQLite版本号，在我的案例中我不想要。我们将非常感谢您的支持

供参考：我的以下内容与此类似：

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没有单个版本号，而版本号可以是多个值

据猜测，您谈论的是Android SDK SQLiteOpenHelper使用的用户_版本

还有application_id，它与user_版本一样可以用作用户变量

您已经遇到了SQLite_版本，因此可以打折

还有data_版本，这不太可能是版本号，因为它用于指示是否实时修改了数据库文件

还有schema_版本，您可能不想将其用作警告：误用此pragma可能会导致数据库损坏

用户版本 如前所述，您可能正在谈论用户版本。首先要注意的是，它是一个用户控制的变量/字段，可供自定义使用。SQlite不使用或更改用户_版本，但允许对其进行更改和使用

此外，诸如DB Browser、Navicat等SQLite管理器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，您必须有意更改user_版本以使其可用，注意如果这样做，并且您使用的是SQLiteOpenHelper的子类，则可能会调用onUpgrade和onDowngrade方法

如果未专门更改用户_版本，并且数据库仅由SQLite管理器工具访问，则其用户_版本将为0。如果数据库文件是通过从使用SQLiteOpenHelper子类的Android应用程序复制数据库文件打开的，则根据用作SQLiteOpenHelper构造函数的第四个参数的最后一个值，它将具有1或更多的用户_版本。当然，如果用户版本是通过编程方式更改的，那么如果文件被复制到SQlite管理器工具中，这种更改也会反映出来

在复制文件之前，通常会在SQlite管理器工具中将用户版本更改为适当的值

您可以使用SQL PRAGMA user_version=5更改用户_版本； 您可以使用PRAGMA user\u version或从PRAGMA\u user\u version中选择*来检索用户\u版本

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用户的版本。否则，您可能必须从assets文件夹中复制文件（可能使用不同的名称），将其作为SQLiteDatabase打开，并使用上面的SQL检索user_版本，然后对照其他值检查它，关闭数据库文件。如果不需要，则删除该文件，否则删除先前的数据库文件，然后重命名复制的文件

实例 下面是一个工作示例，注意到我很少使用Kotlin，这是从java使用AS studio转换而来的

这使用了一个类，即SQLAssetVersionCheck，它从文件中提取版本号，而不是将文件作为SQLiteDatabase打开

SQLAssetVersionCheck.kt：- 结果日志：- 然后在Navicat中关闭连接后将文件复制到assets文件夹，这样我就有两个testdb文件，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

i、 e.新文件的用户_版本为101，因此第一个文件会找到该文件，第二个文件会像以前一样找到文件用户_版本5。

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

PRAGMA user_version = 101;

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