Question

我必须建立一个问题数据库和他们的答案。我使用sqlitedatabase浏览器并放入Assets文件夹。这是我的代码，用于检索特定问题ID的行。

一些重要信息我的数据库名称是extenalDB。我的Tablename有问题;

有coloum：id，question，ans

我必须搜索ID为201的问题。

当我写下我的查询时，问题是.java显示错误ID未声明。

我是stackoverflow的新手，所以如果我不清楚，请询问

这是我的DatabaseHelper类代码

 public class DatabaseHelper extends SQLiteOpenHelper{

//The Android's default system path of your application database.
String DB_PATH =null;

private static String DB_NAME = "extenalDB";

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;
    DB_PATH="/data/data/"+context.getPackageName()+"/"+"databases/";
}    // Creates a empty database on the system and rewrites it with your owndatabase.*/
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");

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

另一个类question.java，点击开始按钮问题答案，他们的id显示在toast消息中。 question.java的代码是。

public class question extends Activity{
Cursor c=null;
int rid=201;

 @Override
    public void onCreate(Bundle savedInstanceState) {
    Intent mintent = getIntent();
        int intValue = mintent.getIntExtra("qtype",0);

        super.onCreate(savedInstanceState);
        setContentView(R.layout.question);


        ((Button)findViewById(R.id.button1)).setOnClickListener(new View.OnClickListener(){
            @Override
            public void onClick(View v) {


                 DatabasseHelper myDbHelper = new DatabasseHelper(question.this);
                 try {

                    myDbHelper.createDataBase();

            } catch (IOException ioe) {

                throw new Error("Unable to create database");

            }

            try {

                myDbHelper.openDataBase();

            }catch(SQLException sqle){

                throw sqle;

            }
            Toast.makeText(question.this, "Success", Toast.LENGTH_SHORT).show();



            c=myDbHelper.query("question", null, id + "=" + rid, null, null,null, null);

                    Toast.makeText(question.this,

                            "id: " + c.getString(0) + "\n" +
                            "question: " + c.getString(1) + "\n" +
                            "ans: " + c.getString(2) + "\n" +

                            Toast.LENGTH_LONG).show();


            }
        });


        }}

Answer 1

你能试试吗

                Cursor executeQuery = myDbHelper
                    .rawQuery(
                            "SELECT ans FROM question where id="+rid,
                    null);
int columnIndex = executeQuery.getColumnIndex("ans");


                if (executeQuery != null) {
                do {
                    Name = executeQuery.getString(columnIndex);
                } while (executeQuery.moveToNext());

如何从数据库中获取数据

1 个答案: