android - 使用预先填充的数据库运送 android 应用程序

Question

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，我什至收到日志 New database has been copyed to device!，但是当我尝试从 db 读取数据时，我得到 no such table异常。

注意:我正在尝试更新我的一个旧应用程序，同样的代码在旧设备版本(如 5.0 及更低版本)中有效，但当我尝试使用最新设备更新应用程序时，它不起作用。

Answer 1

假设您已复制到 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方式隐式打开了数据库调用 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，但在更高版本的 Android 9+ 上，-shm 和 -wal 文件将保持原样，然后数据库将被删除打开，然后由于 -shm 和 -wal 文件与原始空数据库不匹配，检测到损坏，因此创建了一个空的新数据库，因为 SDK 代码试图提供可用的数据库。

• 默认来自 Android 9+ WAL (Write Ahead Logging)默认使用，这是创建和使用 -shm 和 -wal 文件的原因。

有 3 个修复。

• 使用 disableWriteAheadLogging通过重写 SQLiteOpenHelper 类的 onConfigure 方法来实现。然后使用旧的日志模式。

• 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)。

使用第一个可能只会延迟不可避免的事情，并不真正推荐，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，并且作为预防措施还包含第三个修复程序:-

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 上使用以下 Activity 代码进行了测试(以及用于转储架构的附加代码(请注意，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: <<<<<