Question

我遇到了一个问题并绞尽脑汁想弄清楚它为什么不起作用。这是代码

import java.io.*;
import android.content.Context;
import android.database.SQLException;
import android.database.sqlite.*;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;


public class DataBaseHelper extends SQLiteOpenHelper
{
    //The Android's default system path of your application database.
    private static String DB_PATH = "/data/data/teamawesome.spots.namespac/databases/";

    private static String DB_NAME = "Final.db3";

    //private static String DB_TABLE = "Restaurant";

    public 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 String Alphabetical()
{
    Cursor c = null;
    c = (Cursor)myDataBase.query(DB_NAME, null, null, null, null, null, null);
    String sql = "SELECT * FROM Restaurant";
    c = myDataBase.rawQuery(sql, null);
    return c;
}

感谢任何和所有帮助。

谢谢

Answer 1

在你onCreate方法中，你应该做所有在新数据库中创建表的东西，如下所示：

@Override
public void onCreate(SQLiteDatabase db)
{
    db.execSql("create table if not exists Restaraunt (...)");
}

Answer 2

我能够实现几乎没有问题的数据库......我遵循了这个例子：Database Management...这是入门的最好例子。之后还有一些更高级的示例（可以在google中找到），这些示例有助于处理错误捕获和更新等更高级的主题。

Answer 3

如果要复制数据库，还应在SQLiteDatabase.NO_LOCALIZED_COLLATORS调用中使用openDatabase标志。这将导致无法创建LOCALIZED整理器。

您必须缺少未使用指定标志时使用区域设置创建的android-metadata表。然后，你正在复制一个没有它的数据库。

“找不到表格”Android SQLite问题

3 个答案: