无法打开数据库-Android

Question

我正在用SQL开发一个简单的Android应用程序.我按照以下指南 - http://www.reigndesign.com/blog/using-your-own-sqlite-database-in-android-applications/

尝试打开数据库时出错.这是我的DataBaseHelp.Java类 -

public class DataBaseHelper extends SQLiteOpenHelper{

private static String DB_PATH = "/data/data/and.testDB/databases/";

private static String DB_NAME = "MyData";

private SQLiteDatabase myDataBase; 

private final Context myContext;
public DataBaseHelper(Context context) {

 super(context, DB_NAME, null, 1);
    this.myContext = context;
} 
public void createDataBase() throws IOException{

 boolean dbExist = checkDataBase();

 if(dbExist){
  //do nothing - database already exist
 }else{
     this.getReadableDatabase();

     try {

   copyDataBase();

  } catch (IOException e) {

      throw new Error("Error copying database");

     }
 }

}

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;
}

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() {

 //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) {
  }
}

这是我的testDB.Java类 -

public class testDB extends Activity {
SQLiteDatabase myDataBase;
public String[] gur = new String[4];
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    DataBaseHelper myDbHelper = new DataBaseHelper(this);
    myDbHelper = new DataBaseHelper(this);

    try {

        myDbHelper.createDataBase();

} catch (IOException ioe) {

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

}

try {

    myDbHelper.openDataBase();
// Here is the problem-Can't open the database/
}catch(SQLException sqle){

    throw sqle;

}
    myDataBase = myDbHelper.getWritableDatabase();

    Cursor c = myDataBase.rawQuery("SELECT * FROM beer", null);


if (c != null ) {
    if  (c.moveToFirst()) {
          for(int x=0;x< 1;x++)
          {

              gur[x] = (c.getString(c.getColumnIndex("name")));
              c.moveToNext();
          }
}
    Toast.makeText(this,gur[0],Toast.LENGTH_LONG).show();
}


        }
    }

我使用SQLite数据库浏览器创建了数据库,创建了一个名为"beer"的表,添加了2行并将其放在我项目的/ assests文件夹中.

请注意,我是SQL的新手,也是我第一次使用它.我整天都在寻找答案而找不到答案.

谢谢!

Answer 1

您需要在数据库助手（SQLiteOpenHelper 的扩展）的 onCreate 方法中创建数据库。在应用程序上下文中创建数据库之前，对 getReadableDatabase() 的调用不会返回任何内容。

db.execSQL("CREATE TABLE " + TABLE_NAME
+ " (_id INTEGER PRIMARY KEY AUTOINCREMENT,"
+ "foo TEXT, bar TEXT);");

沿着这些思路。显然填写你自己的数据方案。

然后，您可以从资产文件夹中的数据库中读取数据，并使用 sqlite 命令将它们插入到数据库中。

这是我用来入门的教程：

http://www.devx.com/wireless/Article/40842