将数据库文件从/assets复制到文件资源管理器中的/data/data文件夹-Android

Question

在文件资源管理器中将数据库文件从/assets复制到/data/data文件夹时遇到问题。我搜索了这个网站，找到了很多答案，但找不到适合我的答案。我已经用SQLite Manager从外部创建了数据库，并将其导入到assets文件夹中。现在，当我运行我的应用程序时，我在模拟器中得到NullPointerException。我发现包根本没有在/data/data文件夹中创建。但该应用程序正在模拟器中启动。调试器也没有显示任何错误。

我尝试了以下解决方案-

重新启动eclipse和模拟器，删除并重新创建现有模拟器，最终重新启动笔记本电脑

没有一个解决方案能解决我的问题。谁能告诉我，我犯了什么错吗？

这是我的MainActivity.java:-

public class MainActivity extends Activity implements OnClickListener
{
Dialog d;
private photoDbAdapters mDbAdapter;
public int currentimageindex=0;
 String[] sp;   
int p=1;
 @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        images();
 }
 public void images()
 {
        try{
            String rt=mDbAdapter.fetchsingles(); //the application 
                                           is getting crashed in this part
        int id = getResources().getIdentifier(rt, null, null);
        ImageView iv = (ImageView) findViewById(R.id.ImageView3_Left);
        iv.setImageResource(id);
    }catch(NullPointerException er)
{
        String ht=er.toString();
        Toast.makeText(getApplicationContext(), ht, Toast.LENGTH_LONG).show    ();
    }}

@Override
public void onClick(View v)
{
    finish();
    android.os.Process.killProcess(android.os.Process.myPid());
    // TODO Auto-generated method stub
}

fetchsingles方法：-（该方法将从数据库中检索图像文件名）

public String fetchsingles()
{
    try{
img = mDbHelper.getData();

    }catch(Exception e)
    {
        String error= e.toString();
        Dialog d = new Dialog(null);
        d.setTitle("image cannot be fetched");
        int err=Integer.parseInt(error);
        d.setContentView(err);
        d.show();
    }
    return img;

}

getdata方法：-

public String getData() 
{
    // TODO Auto-generated method stub
    String dry="SELECT "+COL_DATA+" FROM Photos WHERE "+COL_ID+"=2;";
        Cursor c = myDataBase.rawQuery(dry,null);
        String result = "";
        int img = c.getColumnIndex(COL_DATA);

            result = c.getString(img);


    return dry;

代码可能看起来很长，不要介意，请帮助我解决这个问题。

提前谢谢。

Answer 1

尝试使用以下代码将数据库从资产复制到data/data/package目录

package com.example.myapp;
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 DataBaseHelper1 extends SQLiteOpenHelper{
      private static String DB_PATH = "/data/data/com.example.myapp/databases/";
      private static String DB_NAME = "myDB.sqlite";
      private SQLiteDatabase myDataBase;
      private final Context myContext;
      public DataBaseHelper1(Context context) 
      {
          super(context, DB_NAME, null, 1);
          this.myContext = context;
      }
      public void createDataBase() throws IOException{

    boolean dbExist = checkDataBase();
      if(dbExist)
      {
          Log.i("DB....", "database available....");
      }
      else
      {
          this.getWritableDatabase();
          try {
          copyDataBase();
          } catch (IOException e) {
          throw new Error("Error copying database");
          }
         Log.i("DB..", "database created.....");
       }   
      }

      public boolean checkDataBase(){
      SQLiteDatabase checkDB = null;
      try{
      String myPath = DB_PATH + DB_NAME;
      checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE);
      }catch(SQLiteException e){
          Log.e("CheckDb","DB not found");
      //database does't exist yet.
      if(checkDB != null){
      checkDB.close();
      }
      }
      finally
      {
          if(checkDB != null){
              checkDB.close();
              } 
          this.close();
      }
      return checkDB != null ? true : false;
      }


      private void copyDataBase() throws IOException{
      InputStream myInput = myContext.getAssets().open(DB_NAME);
      String outFileName = DB_PATH + DB_NAME;
      OutputStream myOutput = new FileOutputStream(outFileName);
          byte[] buffer = new byte[1024];
      int length;
      while ((length = myInput.read(buffer))>0){
      myOutput.write(buffer, 0, length);
      }
      myOutput.flush();
      myOutput.close();
      myInput.close();
      }
      public SQLiteDatabase openDataBase() throws SQLException{
      String myPath = DB_PATH + DB_NAME;
      return myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE);
      }

      @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 void getData()
      {
          SQLiteDatabase myDB ;
          Cursor cursor ;
           try {
                myDB=this.openDataBase();                   
                    cursor=myDB.rawQuery("SELECT * FROM Country_Master",null);

                    if (cursor != null ) {
                       if  (cursor.moveToFirst()) {
                       do {
                           // put your code to get data from cursor                      
                       }while (cursor.moveToNext());
                       }
                    }

                   if(cursor != null)
                    {
                        myDB.close();
                       cursor.close();
                    }                      
                    }catch(SQLException sqle){
                    throw sqle;
                    }

        }
}

还要将此代码放在活动中要复制数据库的onCreate方法下。。

 DataBaseHelper1 myDbHelper = new DataBaseHelper1(MyActivity.this); 
     try 
     {
         myDbHelper.createDataBase();
     }catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            }
     finally
     {
         myDbHelper.close();
     }