我在将数据库文件从/ 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，但找不到适合我背景的答案。我使用SQLite Manager在外部创建了数据库，并将其导入assets文件夹。现在，当我运行我的应用程序时，我在模拟器中得到NullPointerException。我发现根本没有在/ data / data文件夹中创建包。但是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，最后重新启动笔记本电脑
没有一个解决方案解决了我的问题。任何人都可以告诉我，我的错误是什么？
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： - （此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;
代码可能看起来很冗长，不介意任何事情，请帮我解决这个问题。
提前致谢。
答案 0 :(得分：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;
}
}
}
同样将此代码放在您要复制数据库的活动中的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();
}