Question

求大神，android往sqlite中插入时出错

private Button create, updateData, insert, query, update;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_sqlite);
create = (Button)findViewById(R.id.create);
update = (Button)findViewById(R.id.update);
updateData = (Button)findViewById(R.id.updateData);
insert = (Button)findViewById(R.id.insert);
query = (Button)findViewById(R.id.query);
create.setOnClickListener(new CreateListener());
update.setOnClickListener(new UpdateListener());
updateData.setOnClickListener(new UpdateDataListener());
insert.setOnClickListener(new InsertListener());
query.setOnClickListener(new QueryLisetner());

}

class CreateListener implements OnClickListener{
public void onClick(View v) {
// TODO Auto-generated method stub
DatabaseHelper dbHelper = new DatabaseHelper(SQLiteActivity.this, "myDB");
SQLiteDatabase db = dbHelper.getReadableDatabase();
}

}
问题提示：error opening trace file: No such file or directory (2)

android.database.sqlite.SQLiteException: Can't downgrade database from version 2 to 1

at android.database.sqlite.SQLiteOpenHelper.getReadableDatabase(SQLiteOpenHelper.java:188)

Answer 1

创建数据库和版本 ：
----------------------------------------------------------------------------------------------------------------------
public class BarCodeOpenHelper extends SQLiteOpenHelper{
public BarCodeOpenHelper(Context context) {
super(context, "barcode.db", null, 2);
}
@Override
public void onCreate(SQLiteDatabase db) {
String sql = "create table barcode (_id integer auto_increment ,barcode varchar(100))";
db.execSQL(sql);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

}

public Cursor query() {
SQLiteDatabase db = getWritableDatabase();
Cursor c = db.query("barcode", null,null, null, null, null, null);
return c;
}
}

----------------------------------------------------------------------------------------------------------------------
数据库DAO : (只有查询的操作)
----------------------------------------------------------------------------------------------------------------------
public class BarCodeDao {
private BarCodeOpenHelper helper;

public BarCodeDao(Context context) {
helper = new BarCodeOpenHelper(context);
}
public void add(String barcode) {
SQLiteDatabase db = helper.getWritableDatabase();
if (db.isOpen()) {
db.execSQL("insert into barcode (barcode) values (?)",new Object[] {barcode});
db.close();
}
}

注意 ：建库的时候名字是xxx．db　　不是xxx　　。

Answer 2

你要发一下错误，而不是简单的这几句代码啊！这几句代码能看不出什么问题。。。

追问

问题提示：error opening trace file: No such file or directory (2)

android.database.sqlite.SQLiteException: Can't downgrade database from version 2 to 1

at android.database.sqlite.SQLiteOpenHelper.getReadableDatabase(SQLiteOpenHelper.java:188)

追答

你这三句错误，第一句是这个数据库没有建立成功啊。第二句是可能你前面测试填的数据库版本是2，后面测试改成了版本1？版本号只能往上递增的，否则你更新的时候不能把以前的版本给卸载，
第三句就自然是不能打开这个数据库咯？

Answer 3

SQLiteDatabase db = dbHelper.getReadableDatabase();这句话改为
SQLiteDatabase db = dbHelper.getWritableDatabase();