Question

我有一个数据库存储在名为myDatabase.db的资产/数据库中，我想使用此处的代码将其复制到内部存储：

public class DatabaseOpener extends SQLiteOpenHelper {

private static String DB_PATH;

private static String DB_NAME = "table1.db";

private static int DB_VERSION = 4;

private SQLiteDatabase myDataBase;

private static Context myContext;

private static DatabaseOpener instance;

private DatabaseOpener(Context context) {
    super(context, DB_NAME, null, DB_VERSION);
    this.myContext = context;
}

public static synchronized DatabaseOpener getInstance(Context context) {
    if (instance==null) {
        instance = new DatabaseOpener(context);
    }

    if(Build.VERSION.SDK_INT >= 4.2) {
        DB_PATH = myContext.getApplicationInfo().dataDir + "/databases/";
    } else {
        DB_PATH = "/data/data/" + myContext.getPackageName() + "/databases/";
    }
    return instance;
}

public void createDataBase() throws IOException {
    boolean dbExist = checkDataBase();
    if(dbExist) {

    } else {
        this.getReadableDatabase();
        try {
            copyDataBase();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

private boolean checkDataBase(){
    SQLiteDatabase checkDB = null;
    try{
        String myPath = DB_PATH + DB_NAME;
        File file = new File(myPath);
        if (file.exists() && !file.isDirectory()) {
            checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
        }
    }catch(SQLiteException e){
        e.printStackTrace();
    }

    if(checkDB != null){
        checkDB.close();
    }

    return checkDB != null ? true : false;
}

private void copyDataBase() throws IOException{
    //Open your local db as the input stream
    InputStream myInput = myContext.getAssets().open(DB_NAME);

    // Path to the just created empty db
    String outFileName = DB_PATH + DB_NAME;

    //Open the empty db as the output stream
    OutputStream myOutput = new FileOutputStream(outFileName);

    //transfer bytes from the inputfile to the outputfile
    byte[] buffer = new byte[1024];
    int length;
    while ((length = myInput.read(buffer))>0){
        myOutput.write(buffer, 0, length);
    }

    //Close the streams
    myOutput.flush();
    myOutput.close();
    myInput.close();
}

public void openDataBase() throws SQLException {
    String myPath = DB_PATH + DB_NAME;
    File file = new File(myPath);
    if (file.exists() && !file.isDirectory()) {
        myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
    }
}

@Override
public synchronized void close() {
    if(myDataBase != null)
        myDataBase.close();

    super.close();
}

@Override
public void onCreate(SQLiteDatabase db) {

}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

}

上述代码成功运行，直到我卸载了我的应用程序。问题是数据库没有成功复制。我拥有的文件没问题，但是当它被复制到路径中时，如果我把它拿到数据库浏览器中打开它，它就没有表格了。如果我将它推入模拟器，它会再次工作，但我无法将其推入无根设备。唯一的方法是在路径上创建一个DB文件并从资产中复制一个。那么，我做错了什么？另外，这就是我调用DatabaseOpener类的方法：

    DatabaseOpener db = DatabaseOpener.getInstance(context);
    try {
        db.createDataBase();
    } catch (IOException e) {
        throw new Error ("Unable to create database");
    }
    try {
        db.openDataBase();
    }catch(SQLException sqle){
        throw sqle;
    }

    Object object = db.getObjectByName(name);

    db.close();
    return object;

编辑：我收到的错误是android.database.sqlite.SQLiteException: no such table: table1 (code 1): , while compiling。

Answer 1

卸载应用程序后，android会删除与应用程序相关的所有本地数据存储，因此SQLDatabase将被销毁。

当您重新安装应用程序时，您在创建表之前尝试访问它，因此会抛出错误。确保在操作其数据之前创建表。

您需要写入System.out.println((String) arrayList.get(0));

onCreate(SQLiteDatabase db)

Answer 2

我用以下代码解决了这个问题：

public DatabaseOpener(Context context) throws IOException {
    super(context, DB_NAME, null, DB_VERSION);
    this.myContext = context;

    if (Build.VERSION.SDK_INT >= 4.2) {
        DB_PATH = myContext.getApplicationInfo().dataDir + "/databases/";
    } else {
        DB_PATH = "/data/data/" + myContext.getPackageName() + "/databases/";
    }

    boolean dbexist = checkDataBase();
    if (dbexist) {
        openDataBase();
    } else {
        System.out.println("Database doesn't exist");
        createDataBase();
    }
}

public void createDataBase() throws IOException {
    boolean dbexist = checkDataBase();
    if (dbexist) {
        // System.out.println(" Database exists.");
    } else {
        this.getReadableDatabase();
        try {
            copyDataBase();
        } catch (IOException e) {
            throw new Error("Error copying database");
        }
    }
}

private boolean checkDataBase() {
    boolean checkdb = false;
    try {
        String myPath = DB_PATH + DB_NAME;
        File dbfile = new File(myPath);
        checkdb = dbfile.exists();
    } catch (SQLiteException e) {
        System.out.println("Database doesn't exist");
    }
    return checkdb;
}

private void copyDataBase() throws IOException {
    // Open your local db as the input stream
    InputStream myinput = myContext.getAssets().open("databases/" + DB_NAME);

    // Path to the just created empty db
    String outfilename = DB_PATH + DB_NAME;

    // Open the empty db as the output stream
    OutputStream myoutput = new FileOutputStream(DB_PATH + DB_NAME);

    // transfer byte to inputfile to outputfile
    byte[] buffer = new byte[1024];
    int length;
    while ((length = myinput.read(buffer)) > 0) {
        myoutput.write(buffer, 0, length);
    }

    // Close the streams
    myoutput.flush();
    myoutput.close();
    myinput.close();
}

public void openDataBase() throws SQLException {
    // Open the database
    String mypath = DB_PATH + DB_NAME;
    myDataBase = SQLiteDatabase.openDatabase(mypath, null, SQLiteDatabase.OPEN_READWRITE);
}

@Override
public synchronized void close() {
    if (myDataBase != null)
        myDataBase.close();

    super.close();
}

没有这样的表：从资产复制数据库时出现table1错误

2 个答案: