Question

我目前正在使用访问外部数据库的android studio构建我的第一个应用程序。然而，该应用程序崩溃并给出错误，说无法打开数据库。我在youtube上关注了视频，但我仍然遇到了问题。

当我从我的桌面复制我的数据库.sqlite文件并将其粘贴到assets文件夹时，我收到错误“文件加载的编码错误：UTF-8”。我试着用几种编码重新加载文件，但我总是得到相同的错误信息。我猜这是个问题。

欢迎并赞赏任何其他提示或说明。

public class DataBaseHelper extends SQLiteOpenHelper {
    //The Android's default system path of your application database.
    private static String DB_PATH = "/data/data/invain3219/databases/";
    private static String DB_NAME = "partyprobeDB.sqlite";
    private SQLiteDatabase myDataBase;
    private final Context myContext;
    /**
     * Constructor
     * Takes and keeps a reference of the passed context in order to access to the application assets and resources.
     * @param context
     */
    public DataBaseHelper(Context context) {
        super(context, DB_NAME, null, 1);
        this.myContext = context;
    }

    /**
     * Creates a empty database on the system and rewrites it with your own database.
     * */
    public void createDataBase() throws IOException {
        boolean dbExist = checkDataBase();

        if(dbExist){
            //do nothing - database already exist
        }else{
            //By calling this method and empty database will be created into the default system path
            //of your application so we are gonna be able to overwrite that database with our database.
            this.getReadableDatabase();

            try {
                copyDataBase();
            } catch (IOException e) {
                throw new Error("Error copying database");
            }
        }
    }

    /**
     * Check if the database already exist to avoid re-copying the file each time you open the application.
     * @return true if it exists, false if it doesn't
     */
    private boolean checkDataBase(){
        SQLiteDatabase checkDB = null;

        try{
            String myPath = DB_PATH + DB_NAME;
            checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);

        }catch(SQLiteException e){
            //database does't exist yet.
        }

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

        return checkDB != null ? true : false;
    }

    /**
     * Copies your database from your local assets-folder to the just created empty database in the
     * system folder, from where it can be accessed and handled.
     * This is done by transfering bytestream.
     * */
    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 {
        //Open the database
        String myPath = DB_PATH + DB_NAME;
        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) {

    }

    // Add your public helper methods to access and get content from the database.
    // You could return cursors by doing "return myDataBase.query(....)" so it'd be easy
    // to you to create adapters for your views.

}

Answer 1

这看起来不错，但试试这个：

"/data/data/" + context.getPackageName() + "/" + "databases/";

基本上，添加a / after数据库。

修改

public SQLiteDatabase openDataBase() { String myPath = DB_LOCATION + DATABASE_NAME; myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY); return null; }

复制

private void copyDataBase() throws IOException { InputStream myInput = myContext.getAssets().open(DATABASE_NAME); String outFileName = DB_LOCATION + DATABASE_NAME; OutputStream myOutput = new FileOutputStream(outFileName); byte[] buffer = new byte[10]; int length; while ((length = myInput.read(buffer)) > 0) { myOutput.write(buffer, 0, length); } myOutput.flush(); myOutput.close(); myInput.close(); }

Answer 2

id是int，所以如下所示更改就足够了，你不需要这样" WHERE " + TableInfo.INFO_USER + " = '" + id + "';"

 int id = curs.getInt(0);

    curs = db.rawQuery("SELECT * FROM " + TableInfo.TABLE_USER_INFO +
            " WHERE " + TableInfo.INFO_USER + " = " + id, null);

android studio无法打开.sqlite数据库文件

2 个答案: