没什么好说的，只是粘贴我的代码，希望有人能看到我缺少的东西:

数据库.Java

package gr.peos;

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 Database extends SQLiteOpenHelper{

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

//Name of the Database to be created.
private static String DB_NAME = "BLib";

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 Database(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{

    //First we check if the database already exists, Method declared later
    boolean dbExist = checkDataBase(); 

    if(dbExist){
        //do nothing - database already exists
    }else{

        //By calling this method an empty database will be created into the default system path
           //of your application so we are going to be able to overwrite that database with our database.
        this.getReadableDatabase();

        try {
            copyDataBase(); //Method declared later

        } 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 transferring byte stream.
 * */

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();

}




//Opening the Database
public void openDataBase() throws SQLException{

    //Open the database
    String myPath = DB_PATH + DB_NAME;
    myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);

}


/
//Finally overriding a few methods as required

@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) {

}

调用它的部分是在我的主要 Activity 的 onCreate 方法上(也试过其他人，这不是问题)。

 Database myDbHelper = new Database(null);
    myDbHelper = new Database(this);

    try {
        myDbHelper.createDataBase();

    } catch (IOException ioe) {

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

try {



}catch(SQLException sqle){

    throw sqle;

  }

现在是奇怪的部分。在我的设备上(我没有 root 访问权限，所以在创建数据库后无法提取它)，我的数据似乎是 48KB。在模拟器上运行完全相同的代码时，数据库不会被复制(我没有选择任何异常)。确切地说，android/元数据表似乎被复制了，但其他表和数据都没有。有什么想法吗？

最佳答案

我给你完整的代码，如果成功请回复

public class DataBaseHelper extends SQLiteOpenHelper{
private Context mycontext;

private String DB_PATH = "/data/data/gr.peos/databases/";
//private String DB_PATH = mycontext.getApplicationContext().getPackageName()+"/databases/";
private static String DB_NAME = "BLib.sqlite";//the extension may be .sqlite or .db
public SQLiteDatabase myDataBase;
/*private String DB_PATH = "/data/data/"
                            + mycontext.getApplicationContext().getPackageName()
                            + "/databases/";*/

public DataBaseHelper(Context context) throws IOException  {
    super(context,DB_NAME,null,1);
    this.mycontext=context;
    boolean dbexist = checkdatabase();
    if(dbexist)
    {
        //System.out.println("Database exists");
        opendatabase(); 
    }
    else
    {
        System.out.println("Database doesn't exist");
    createdatabase();
    }

}

public void createdatabase() throws IOException{
    boolean dbexist = checkdatabase();
    if(dbexist)
    {
        //System.out.println(" Database exists.");
    }
    else{
        this.getReadableDatabase();
    try{
            copydatabase();
        }
        catch(IOException e){
            throw new Error("Error copying database");
        }
    }
}
private boolean checkdatabase() {
    //SQLiteDatabase checkdb = null;
    boolean checkdb = false;
    try{
        String myPath = DB_PATH + DB_NAME;
        File dbfile = new File(myPath);
        //checkdb = SQLiteDatabase.openDatabase(myPath,null,SQLiteDatabase.OPEN_READWRITE);
        checkdb = dbfile.exists();
    }
    catch(SQLiteException e){
        System.out.println("Database doesn't exist");
    }

    return checkdb;
}
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("/data/data/gr.peos/databases/BLib.sqlite");

    // transfer byte to inputfile to 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_READWRITE);

}



public synchronized void close(){
    if(myDataBase != null){
        myDataBase.close();
    }
    super.close();
}

关于java - 数据库不从 Assets 复制，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/5945196/