Question

首先，请勿将此问题标记为重复。我搜索了所有可能的选项并尝试了它们但它仍然无效。更改了数据库版本，清除了数据并重新安装了应用程序。我将数据库正确放置在数据库文件夹中。编译错误时仍然没有找到这样的表。帮我弄清楚我在这段代码中缺少什么，或者我做错了什么。

public class DatabaseHelper extends SQLiteOpenHelper {


    String DB_PATH = null;
    private static String DB_NAME = "externaldatabase";
    private SQLiteDatabase myDataBase;
    private final Context myContext;
    Cursor c =null;

    public DatabaseHelper(Context context) {
        super(context, DB_NAME, null, 11);
        this.myContext = context;
        this.DB_PATH = "/data/data/" + context.getPackageName() + "/" + "databases/";
        Log.e("Path 1", DB_PATH);
    }

    public void createDataBase() throws IOException {
        boolean dbExist = checkDataBase();
        if (dbExist) {
        } else {
            this.getReadableDatabase();
            try {
                copyDataBase();
            } catch (IOException e) {
                e.toString();
            }
        }
    }

    private boolean checkDataBase() {
        SQLiteDatabase checkDB = null;
        try {
            String myPath = DB_PATH + DB_NAME;
            checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
        } catch (SQLiteException e) {
        }
        if (checkDB != null) {
            checkDB.close();
        }
        return checkDB != null ? true : false;
    }

    private void copyDataBase() throws IOException {
        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();

    }

    public void openDataBase() throws SQLException {
        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) {
        if (newVersion > oldVersion)
            try {
                copyDataBase();
            } catch (IOException e) {
                e.printStackTrace();

            }
    }



    public Cursor query(String table, String[] columns, String selection, String[] selectionArgs, String groupBy, String having, String orderBy) {
        return myDataBase.query("rates_table", null, null, null, null, null, null);
    }


    public String getFare(String name, String depart){

        SQLiteDatabase db = this.getReadableDatabase();


        String [] columns = {"rate"};

        c = db.rawQuery("select rate from rates_table where place1 = '"+name+"'and place3 = '"+depart+"' or place1 = '"+depart+"'and place3 = '"+name+"'", new String[]{});


        StringBuffer buffer = new StringBuffer();
        while(c.moveToNext()){

            String employyename = c.getString(0);


            buffer.append(employyename+"");
        }

        return buffer.toString();

    } }

Answer 1

您在onCreate()方法中没有任何代码。在createDatabase()内调用onCreate()方法。

@Override
public void onCreate(SQLiteDatabase db) {
    createDataBase();
}

使用AssetManager从资产文件夹中读取文件
使用Stetho检查数据库是否实际创建。

Answer 2

你没有在onCreate（）中为表创建编写任何代码。请注意SQLiteOpenHelper类： -

onCreate（） - 这是我们需要编写create table的地方声明。在创建数据库时调用此方法。
onUpgrade（） - 在升级数据库时调用此方法修改表结构，向数据库添加约束等，

所以在onCreate（）中你必须为create table编写逻辑。

SQLite异常：找不到这样的表

2 个答案: