无法在Android应用中使用外部数据库

Question

我想在MySQL中使用我的外部数据库。 我有一个存档数据库databse.db.zip并将其复制到我的Android Java项目的assets文件夹中。 最后，我创建了一个用于打开数据库的类：

import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteQueryBuilder;
import com.readystatesoftware.sqliteasset.SQLiteAssetHelper;

public class databaseOpen extends SQLiteAssetHelper {

private static final String DATABASE_NAME = "parole.db";
private static final int DATABASE_VERSION = 1;

public databaseOpen(Context context) {

    super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
public String risposta(String parolain ){
    SQLiteDatabase db = getReadableDatabase();
    SQLiteQueryBuilder qb = new SQLiteQueryBuilder();
    String[] selectionArgs = {"ciao"};
    Cursor c =db.query("prima", null, null,selectionArgs, null, null,   null);
    c.moveToFirst();

    return c.getString(0);
}
}

我已经在我的main回收它：

private databaseOpen db;

@Override
protected void onCreate(Bundle savedInstanceState) {
    db = new databaseOpen(this);
    Toast toast=Toast.makeText(this, db.risposta("ciao"), Toast.LENGTH_LONG);
}

但这不起作用。 这是我得到的输出：

09-26 15:20:23.761    1099-1099/? I/SQLiteAssetHelper successfully opened database parole.db
09-26 15:20:23.764    1099-1099/? E/SQLiteLog (1) no such table: prima
09-26 15:20:23.783    1099-1099/? D/AndroidRuntime Shutting down VM
09-26 15:20:23.801    1099-1099/? E/AndroidRuntime FATAL EXCEPTION: main
    Process: com.example.roby.jarvis, PID: 1099
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.roby.jarvis/com.example.roby.jarvis.Home}: android.database.sqlite.SQLiteException: no such table: prima (code 1): , while compiling: SELECT * FROM prima

Answer 1

我想在mysql中使用我的外部datbase，我已经将其压缩（databse.db.zip），并将其复制到我的Java项目的assents文件夹中

为了记录，您使用的术语错误或感到困惑。 Android和您帖子中的代码可与SQLite一起使用。 它不适用于MySQL。

当某些事情不起作用时，请阅读错误消息，该消息通常可以解释问题，例如：

09-26 15：20：23.764 1099-1099 /？ E / SQLiteLog：（1）没有这样的表：prima

文件中不存在名为“ prima”的表。

调试的下一步是使用sqlite3命令行工具或类似工具检查PC上文件的内容，并查看文件中包含哪些表（ .schema命令）。

Answer 2

第一：您没有将Database文件从资产文件复制到设备，这显然会导致no such table found 。

试试这个代码，它对我有用。 （我也评论了不同的部分，以供您理解）

import android.content.ContentValues;
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.os.Build;
import android.util.Log;

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

/**
* Created by HP-HP on 23-07-2015.
*/
public class DataBaseHelper extends SQLiteOpenHelper {

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

private static String DB_NAME = "profanityv2";

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);

    if(android.os.Build.VERSION.SDK_INT >= 4.2){
        DB_PATH = context.getApplicationInfo().dataDir + "/databases/";
    } else {
        DB_PATH = "/data/data/" + context.getPackageName() + "/databases/";
    }

    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.
        try {
            myContext.deleteDatabase("profanity");
        } catch (Exception e1) {
            e1.printStackTrace();
        }
    }

    if(checkDB != null){

        checkDB.close();

    }

    return checkDB != null;
}

/**
 * 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.NO_LOCALIZED_COLLATORS|SQLiteDatabase.CREATE_IF_NECESSARY );

}

@Override
public synchronized void close() {

    if(myDataBase != null)
        myDataBase.close();

    super.close();

}

public Cursor getData() {
    Cursor c = null;
    try {
        c = myDataBase.rawQuery("SELECT * FROM profanity_table", null);
    } catch (Exception e) {
        e.printStackTrace();
    }
    // Note: Master is the one table in External db. Here we trying to access the records of table from external db.
    return c;
}


@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.

}

用法：

DataBaseHelper dataBaseHelper = new DataBaseHelper(this);

    try {
        dataBaseHelper.createDataBase();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

    try {

        dataBaseHelper.openDataBase();

    }catch(SQLException sqle){

        throw sqle;

    }

    Cursor c = dataBaseHelper.getData();

    if(c!=null) {
        /* your cursor code */
        c.close();
    }


    dataBaseHelper.close();

*注意：某些设备可能无法将数据库复制到该设备。（已知设备：OnePlus）

不要忘记添加此权限

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

在你的清单上。

编辑1： OnePlus能够将数据库复制到/ /data/data/<package-name>/databases/<filename>.db <程序包名称> / databases / <文件名> /data/data/<package-name>/databases/<filename>.db但是它不允许访问该数据，我/data/data/<package-name>/databases/<filename>.db 。