Android中访问数据库的问题,表isn';不要被创造
看起来数据库已经创建了,但是当我尝试访问创建的数据库时,出现了错误。每当调用Android中访问数据库的问题,表isn';不要被创造,android,runtime-error,android-sqlite,sqliteopenhelper,Android,Runtime Error,Android Sqlite,Sqliteopenhelper,看起来数据库已经创建了,但是当我尝试访问创建的数据库时,出现了错误。每当调用doQuery()时,应用程序就会崩溃。你能帮我找出我做错了什么吗 private class LoadCursorTask extends AsyncTask<Void, Void, Void> { Cursor constantCursor=null; @Override protected Void doInBackground(Void.
doQuery()
时,应用程序就会崩溃。你能帮我找出我做错了什么吗
private class LoadCursorTask extends AsyncTask<Void, Void, Void>
{
Cursor constantCursor=null;
@Override
protected Void doInBackground(Void... params)
{
// TODO Auto-generated method stub
Log.d("Action1","in doInBacground()");
constantCursor=doQuery();
Log.d("Action1","after doQuery ");
constantCursor.getCount();
return null;
}
}
private Cursor doQuery()
{
Log.d("Action1","in doQuery()");
Cursor localCursor= db.getReadableDatabase().rawQuery("SELECT _id, title, value"+" FROM constants ORDER BY title; ", null);
Log.d("Action1","before returning from doQuery()");
return localCursor;
}
[更新1]
这是DatabaseHelper.class
public class DatabaseHelper extends SQLiteOpenHelper
{
private static final String DATABASE_NAME="constants.db";
private static final int SCHEMA=1;
static final String TITLE="title";
static final String VALUE="value";
static final String TABLE="constants";
public DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, SCHEMA);
// TODO Auto-generated constructor stub
Log.d("Action1","in DatabaseHelper constructor");
}
@Override
public void onCreate(SQLiteDatabase db)
{
Log.d("Action1","in onCreate");
try
{
db.beginTransaction();
db.execSQL("CREATE TABLE constants (_id INTEGER PRIMARY KEY AUTOINCREMENT, title TEXT, value REAL)");
ContentValues cv=new ContentValues();
cv.put(TITLE, "Gravity, Death Star I");
cv.put(VALUE, SensorManager.GRAVITY_DEATH_STAR_I);
db.insert("constants", TITLE, cv);
cv.put(TITLE, "Gravity, Earth");
cv.put(VALUE, SensorManager.GRAVITY_EARTH);
db.insert("constants", TITLE, cv);
cv.put(TITLE, "Gravity, Jupiter");
cv.put(VALUE, SensorManager.GRAVITY_JUPITER);
db.insert("constants", TITLE, cv);
}
finally
{
db.endTransaction();
}
}
}
它可能找不到您的数据库文件,并在您尝试打开它时创建一个新的空文件。检查数据库的名称和位置。如果您是在代码中创建的,请确保在尝试访问该表之前创建该表 编辑: 发现问题后,需要在endTransaction之前将事务标记为成功,否则它将回滚
@Override
public void onCreate(SQLiteDatabase db)
{
Log.d("Action1","in onCreate");
try
{
db.beginTransaction();
db.execSQL("CREATE TABLE constants (_id INTEGER PRIMARY KEY AUTOINCREMENT, title TEXT, value REAL)");
ContentValues cv=new ContentValues();
cv.put(TITLE, "Gravity, Death Star I");
cv.put(VALUE, SensorManager.GRAVITY_DEATH_STAR_I);
db.insert("constants", TITLE, cv);
cv.put(TITLE, "Gravity, Earth");
cv.put(VALUE, SensorManager.GRAVITY_EARTH);
db.insert("constants", TITLE, cv);
cv.put(TITLE, "Gravity, Jupiter");
cv.put(VALUE, SensorManager.GRAVITY_JUPITER);
db.insert("constants", TITLE, cv);
db.setTransactionSuccessful();
}
finally
{
db.endTransaction();
}
}
嗯。。。。“原因:android.database.sqlite.SQLiteException:没有这样的表:常量(代码1)”没有这样的表:常量。在数据库中创建常量tableremove“;”创建行。创建数据库的数据库助手类的post代码。因此,did
db.execSQL(..
part是否在其他代码之前运行过?好的,我检查数据库是否是通过DDMS文件浏览器创建的,是的,数据库文件在那里。但是,在检查数据库时,表似乎没有创建。因此,正如您所说的,这是一个问题。抱歉,如果我听起来很幼稚,但我似乎无法找出原因没有创建e表。您能在这里帮助我吗?:\n在使用endTransaction之前使用db.setTransactionSuccessful()。已编辑的answer.Finally。现在效果很好。非常感谢:)注意onCreate()
已在事务中运行,因此启动嵌套事务不会增加任何好处,只会增加代码大小和复杂性。根据,这是正确的。因此,我们可以省去开始事务
和结束事务
。
public class DatabaseHelper extends SQLiteOpenHelper
{
private static final String DATABASE_NAME="constants.db";
private static final int SCHEMA=1;
static final String TITLE="title";
static final String VALUE="value";
static final String TABLE="constants";
public DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, SCHEMA);
// TODO Auto-generated constructor stub
Log.d("Action1","in DatabaseHelper constructor");
}
@Override
public void onCreate(SQLiteDatabase db)
{
Log.d("Action1","in onCreate");
try
{
db.beginTransaction();
db.execSQL("CREATE TABLE constants (_id INTEGER PRIMARY KEY AUTOINCREMENT, title TEXT, value REAL)");
ContentValues cv=new ContentValues();
cv.put(TITLE, "Gravity, Death Star I");
cv.put(VALUE, SensorManager.GRAVITY_DEATH_STAR_I);
db.insert("constants", TITLE, cv);
cv.put(TITLE, "Gravity, Earth");
cv.put(VALUE, SensorManager.GRAVITY_EARTH);
db.insert("constants", TITLE, cv);
cv.put(TITLE, "Gravity, Jupiter");
cv.put(VALUE, SensorManager.GRAVITY_JUPITER);
db.insert("constants", TITLE, cv);
}
finally
{
db.endTransaction();
}
}
}
@Override
public void onCreate(SQLiteDatabase db)
{
Log.d("Action1","in onCreate");
try
{
db.beginTransaction();
db.execSQL("CREATE TABLE constants (_id INTEGER PRIMARY KEY AUTOINCREMENT, title TEXT, value REAL)");
ContentValues cv=new ContentValues();
cv.put(TITLE, "Gravity, Death Star I");
cv.put(VALUE, SensorManager.GRAVITY_DEATH_STAR_I);
db.insert("constants", TITLE, cv);
cv.put(TITLE, "Gravity, Earth");
cv.put(VALUE, SensorManager.GRAVITY_EARTH);
db.insert("constants", TITLE, cv);
cv.put(TITLE, "Gravity, Jupiter");
cv.put(VALUE, SensorManager.GRAVITY_JUPITER);
db.insert("constants", TITLE, cv);
db.setTransactionSuccessful();
}
finally
{
db.endTransaction();
}
}