Question

我有一个数据库，我已将其放在我的资源文件夹中，并且我正在使用此DataBaseHelper类。

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;

public class DataBaseHelper extends SQLiteOpenHelper{

    //The Android's default system path of your application database.
    private static String DB_PATH = "/data/data/com.example.onlywithalcohol/databases/";

    private static String DB_NAME = "Alcohol_DB";

    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) {

    }

    public boolean isOpen()
    {
        Log.v("test",myDataBase.getPath());
        return myDataBase.isOpen();
    }

    public Cursor selectRecord(int id){
        Cursor c =myDataBase.rawQuery("Select title from alcorecords where id="+id, null);
          Log.v("test", c.toString());
        return c;
    }


        // 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.

任何人都可以告诉我如何制作简单的选择功能。我已经完成了这个功能

 public Cursor selectRecord(int id){
        Cursor c =myDataBase.rawQuery("Select title from alcorecords where id="+id, null);
          Log.v("test", c.toString());
        return c;
    }

但是它让我错误地告诉我数据库中没有这样的表。我该怎么做才能使这个宝宝工作：）

Answer 1

上周我遇到了类似的问题。我认为您需要将文件扩展名追加到DB_NAME，因此它会变为"Alcohol_DB.sqlite"或".db"。你得到mehasage “数据库中没有这样的表”的原因是创建了一个空数据库，即使它没有从你的资源中复制数据库也很困难。

<强>提示：

如果您对数据库进行任何处理，则应删除模拟器上的应用程序数据，以便复制新数据库。为此，请转到Settings->Applications->Manage applications->YOUR_APP->Clear data。

如果使用Eclipse，则可以通过从模拟器下载数据库文件来检查文件是否已被复制。为此，您需要在Eclipse Window->Open perspective->Other...->DDMS中打开DDMS透视图。选择左侧的模拟器，然后转到“文件资源管理器”选项卡。您将在data/data/your.package.name/database/中找到您的数据库。选择文件，然后按标签右上角的“拉文件”按钮。您现在可以使用首选的SQLite管理器检查文件。

希望这有帮助！

修改

我还将代码中的checkDataBase()更改为：

private boolean checkDataBase(){ String myPath = DB_PATH + DB_NAME; File dbFile = new File(myPath); return dbFile.exists(); }

数据库android从表中选择

1 个答案: