Question

我在sqlite studio中创建了一个数据库，我将其导入到我的Android应用程序中。 SQLite帮助程序代码如下：

public class DatabaseHelper extends SQLiteOpenHelper {


String DB_PATH = null;
private static String DB_NAME = "mydatabases";
private static SQLiteDatabase myDataBase;
private final Context myContext;

public DatabaseHelper(Context context) {
    super(context, DB_NAME, null, 21);
    this.myContext = context;
    this.DB_PATH = "/data/data/" + context.getPackageName() + "/" + "databases/";

    Log.e("Path 1", DB_PATH);
}



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


@Override
public void onCreate(SQLiteDatabase db) {
    try {
        InputStream myInput = myContext.getAssets().open(DB_NAME);
        String outFileName = DB_PATH + DB_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();
    }
    catch(IOException ex){}

}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    if (newVersion > oldVersion){
        try {
            InputStream myInput = myContext.getAssets().open(DB_NAME);
            String outFileName = DB_PATH + DB_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();
        } catch (IOException e) {
            e.printStackTrace();

        }
    }
}

现在我想从数据库中获取数据，下面是在活动加载中检索数据的代码：

onActivityCreated代码：

 public void onActivityCreated(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onActivityCreated(savedInstanceState);
    final ArrayList<String> strArary;
    myDbHelper = new DatabaseHelper(getActivity());
    c = myDbHelper.getReadableDatabase().rawQuery("SELECT * FROM categories",null) ; // myDbHelper.query("categories",null,null,null,null,null,null);

 if (c.moveToFirst()) {
        do {
            strArary1.add(c.getString(0));
            strArary.add(c.getString(1));

        } while (c.moveToNext());
    }

鉴于代码提出了一些错误，如问题标题所述。

请帮我解决问题。

Answer 1

这是我的课，对我来说很好用：

public class DBHandler extends SQLiteOpenHelper {

    private static final String DataBase_Name = "yourdb";
    private static final int DataBase_Version = 3;
    private static final String Path ="/data/data/" + context.getPackageName() + "/" + "databases/";
    public Cursor cursor;
    protected Context context;
    SQLiteDatabase DB;
    String url;

    public DBHandler(Context context) {
        super(context, DataBase_Name, null, DataBase_Version);
        this.context = context;

        try {
            OpenDataBase();
            Close();
        } catch (Exception e) {
            System.out.println(e.getMessage());
        }
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
    }

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

    private void CopyDataBase() throws IOException {

        InputStream myinput = context.getAssets().open(DataBase_Name);
        String output = Path + DataBase_Name;

        OutputStream myoutputstream = new FileOutputStream(output);
        byte[] buffer = new byte[1024];
        int length;

        try {
            while ((length = myinput.read(buffer)) >= 0) {
                myoutputstream.write(buffer, 0, length);
            }
            myoutputstream.flush();
            myoutputstream.close();
            myinput.close();
        } catch (Exception e) {
            System.out.println(e.getMessage());
        }

    }

    protected boolean ChekDB() {
        SQLiteDatabase exist = null;
        try {
            String DBPath = Path + DataBase_Name;
            exist = SQLiteDatabase.openDatabase(DBPath, null, SQLiteDatabase.OPEN_READWRITE);
            if (DataBase_Version > exist.getVersion()) {
                exist.close();
                CopyDataBase();
                exist = SQLiteDatabase.openDatabase(DBPath, null, SQLiteDatabase.OPEN_READWRITE);
                exist.setVersion(DataBase_Version);
                Util.saveDataToShared(context, "sync", "fixedInserted", "");
            }


        } catch (SQLiteException e) {
            System.out.println(e.getMessage());
        } catch (IOException e) {
            e.printStackTrace();
        }
        if (exist != null) {
            exist.close();
        }
        return exist != null ? true : false;

    }

    private void OpenDataBase() throws SQLDataException {

        if (ChekDB()) {

            String DBPath = Path + DataBase_Name;
            DB = SQLiteDatabase.openDatabase(DBPath, null, SQLiteDatabase.OPEN_READWRITE);
        } else {
            this.getWritableDatabase();
            try {
                CopyDataBase();
            } catch (IOException e) {
                System.out.println(e.getMessage());
            }
        }


    }

    public Cursor Select(String Query) {

        try {
            OpenDataBase();
            cursor = DB.rawQuery(Query, null);
        } catch (SQLDataException e) {
            if (e!=null&&e.getMessage()!=null)
                Log.e("Handler - Select :",e.getMessage());
        }

        return cursor;
    }

    /**
     * @param tableName
     * @param contentValues
     * @param whereClause
     * @param args
     * @return Rows Effected
     */
    protected int update(String tableName, ContentValues contentValues, String whereClause, String[] args) {
        try {
            OpenDataBase();
        } catch (SQLDataException e) {
            System.out.println(e.getMessage());
        }
        int result = DB.update(tableName, contentValues, whereClause, null);
        DB.close();
        return result;
    }

    /**
     * @param tableName
     * @param whereClause
     * @param args
     * @return Rows Effected
     */
    protected int delete(String tableName, String whereClause, String[] args) {
        try {
            OpenDataBase();
        } catch (SQLDataException e) {
            System.out.println(e.getMessage());
        }
        int result = DB.delete(tableName, whereClause, args);
        DB.close();
        return result;
    }

    protected long insert(String Table_Name, ContentValues V) {
        long rowid = -1;
        try {
            OpenDataBase();
            rowid = DB.insert(Table_Name, null, V);
            System.out.println(rowid);
            DB.close();
        } catch (Exception e) {
            if (e!=null&&e.getMessage()!=null)
              Log.e("Inserting to Table "+Table_Name,e.getMessage());
            DB.close();
        }
        return rowid;
    }

    protected void ExecuteQuery(String Q) {
        try {
            OpenDataBase();
            DB.execSQL(Q);
            DB.close();
        } catch (Exception e) {
            System.out.println("ExecuteQuery " + e.getMessage());
        }
    }

    public void Close() {
        if (DB != null)
            DB.close();
        if (cursor != null && !cursor.isClosed())
            cursor.close();
    }

    public void WhenUpGrade() {
        try {
            String assetPath = context.getAssets().toString() + "/" + DataBase_Name;
            SQLiteDatabase assetDB = SQLiteDatabase.openDatabase(assetPath, null, SQLiteDatabase.OPEN_READWRITE);
            SQLiteDatabase oldDB = SQLiteDatabase.openDatabase(Path + DataBase_Name, null, SQLiteDatabase.OPEN_READWRITE);
            Log.d("", assetDB != null ? "" : "");
            Log.d("", oldDB != null ? "" : "");
        } catch (Exception e) {
            if (e != null && e.getMessage() != null)
                Log.e("upgradingDB", e.getMessage());
        }
    }


}

从sqlite数据库的物理副本创建数据库时SQL（查询）错误或缺少数据库

1 个答案: