Question

我正在使用SQL开发一个简单的Android应用程序。我按照以下指南 - Using your own SQLite database in Android applications

尝试对数据库进行查询时出错。

这是我的DataBaseHelp.Java类：

package namae.nombebe;

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

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

public class DataBaseHelper extends SQLiteOpenHelper{

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

    private static String DB_NAME = "myDBName";

    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.

}

这是我打开数据库的方式：

    public void onCreate(Bundle savedInstanceState) 
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        DataBaseHelper myDbHelper = new DataBaseHelper(this);

        try 
        {
                myDbHelper.createDataBase();
        } 
        catch (IOException ioe) 
        {
            throw new Error("Unable to create database");
        }

        try 
        {
            myDbHelper.openDataBase();
        }
        catch(SQLException sqle)
        {
            throw sqle;
        }

        myDataBase = myDbHelper.getWritableDatabase();

        Cursor c = myDataBase.rawQuery("SELECT * FROM Astuces", null);
// problem on this query
    }

因此查询不起作用。（如果我不把它的应用程序工作）

我有一张表Astuces。

错误：

07-30 10:56:53.869: E/AndroidRuntime(503): java.lang.RuntimeException: Unable to start activity ComponentInfo{namae.nombebe/namae.nombebe.NomBebeActivity}: android.database.sqlite.SQLiteException: no such table: Astuces: , while compiling: SELECT * FROM Astuces

我们可以看到我说没有表格Astuces我真的拥有它所以我不明白为什么我能找到它。

Answer 1

几周前我跟着同一个链接。在开始使用代码之前，您必须考虑一些重要事项：

1 - 您需要在SQLite file来电android_metadata中添加一个表格，然后将en_US插入其中。

2 - 您必须将id重命名为_id。

3 - 您应该将SQLite文件复制到项目的assets文件夹中。

然后你可以使用这些代码。你是如何完成这3个步骤的？

myDataBase班级在哪里？您在代码中的哪个位置实现了这些方法？

myDataBase = myDbHelper.getWritableDatabase();
Cursor c = myDataBase.rawQuery("SELECT * FROM Astuces", null);

您可能需要在DataBaseHelper班级

中使用此类内容

public Cursor fetchAllEntries() {
            //includes all column names
        String[] projection = new String[] { KEY_ROWID, USER_ID, START, END };
        String restrict = null; // Get all entries
            String orderby = null;
        return myDataBase.query(TABLE_NAME, projection, restrict, null, null, null, orderby);
    }

并在主要活动中将其称为：

Cursor entryCursor = db.fetchAllEntries();

查询不起作用数据库android

1 个答案: