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有關android開發，我只是試圖創建一個SQL數據庫時首次啓動活動（使用首選項）。活動第二次啓動時，它應該從數據庫檢索數據並輸出日誌消息。首次啓動時創建SQL數據庫，並在下次啓動時檢索數據庫數據
我第一次設法啓動活動（即時假設數據庫是在這裏創建的），但第二次我得到一個IllegalStateException錯誤：從第0行到第1列的字段插槽失敗。不確定我在哪裏出錯了。有人可以檢查嗎？由於
主要類
public class MainMenu extends Activity implements OnClickListener{
private ModulesDbAdapter mpDbHelper;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
//create database here
SharedPreferences initialPref = getSharedPreferences("INITIAL", 0);
boolean firsttimer = initialPref.getBoolean("INITIAL", false);
if (!firsttimer){
//create database here
mpDbHelper = new ModulesDbAdapter(this);
mpDbHelper.open();
long id1 = mpDbHelper.createReminder("Hello1", "Test 1", "Date1");
long id2 = mpDbHelper.createReminder("Hello2", "Test 2", "Date2");
long id3 = mpDbHelper.createReminder("Hello3", "Test 3", "Date3");
/*Cursor c = mpDbHelper.fetchModules((String)"CS118");
Log.d("TESTING",c.getString(c.getColumnIndex("KEY_MOD_NAME")));*/
//get boolean preference to true
SharedPreferences.Editor editorPref = initialPref.edit();
editorPref.putBoolean("INITIAL", true);
editorPref.commit();
}else {
fetchData();
}
}
private void fetchData(){
mpDbHelper = new ModulesDbAdapter(this);
mpDbHelper.open();
long input = 2;
Cursor c = mpDbHelper.fetchReminder(input);
startManagingCursor(c);
Log.d("TESTING",c.getString(c.getColumnIndex("KEY_BODY")));
}
/*@Override
protected void onPause() {
super.onPause();
mpDbHelper.close();
}
@Override
protected void onStop() {
super.onPause();
mpDbHelper.close();
}*/
}
}
適配器類
public class ModulesDbAdapter {
private static final String DATABASE_NAME = "data";
private static final String DATABASE_TABLE = "reminders";
private static final int DATABASE_VERSION = 1;
public static final String KEY_TITLE = "title";
public static final String KEY_BODY = "body";
public static final String KEY_DATE_TIME = "reminder_date_time";
public static final String KEY_ROWID = "_id";
private DatabaseHelper mDbHelper;
private SQLiteDatabase mDb;
//defines the create script for the database
private static final String DATABASE_CREATE =
"create table " + DATABASE_TABLE + " ("
+ KEY_ROWID + " integer primary key autoincrement, "
+ KEY_TITLE + " text not null, "
+ KEY_BODY + " text not null, "
+ KEY_DATE_TIME + " text not null);";
//Context object that will be associated with the SQLite database object
private final Context mCtx;
//The Context object is set via the constructor of the class
public ModulesDbAdapter(Context ctx) {
this.mCtx = ctx;
}
//helps with the creation and version management of the SQLite database.
private static class DatabaseHelper extends SQLiteOpenHelper {
//call made to the base SQLiteOpenHelper constructor. This call creates, opens, and/or manages a database
DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL(DATABASE_CREATE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion,int newVersion) {
// Not used, but you could upgrade the database with ALTER
// Scripts
}
}
//now create the database by calling the getReadableDatabase()
public ModulesDbAdapter open() throws android.database.SQLException {
mDbHelper = new DatabaseHelper(mCtx);
mDb = mDbHelper.getWritableDatabase();
return this;
}
//close the database
public void close() {
mDbHelper.close();
}
public long createReminder(String title, String body, String
reminderDateTime) {
ContentValues initialValues = new ContentValues();
initialValues.put(KEY_TITLE, title);
initialValues.put(KEY_BODY, body);
initialValues.put(KEY_DATE_TIME, reminderDateTime);
//insert row into database
return mDb.insert(DATABASE_TABLE, null, initialValues);
}
public boolean deleteReminder(long rowId) {
return mDb.delete(DATABASE_TABLE, KEY_ROWID + "=" + rowId, null) > 0;
}
//utilizes the query() method on the SQLite database to find all the reminders in the system
public Cursor fetchAllReminders() {
return mDb.query(DATABASE_TABLE, new String[] {KEY_ROWID, KEY_TITLE,
KEY_BODY, KEY_DATE_TIME}, null, null, null, null, null);
}
public Cursor fetchReminder(long rowId) throws SQLException {
Cursor mCursor =
mDb.query(true, DATABASE_TABLE, new String[] {KEY_ROWID,
KEY_TITLE, KEY_BODY, KEY_DATE_TIME}, KEY_ROWID + "=" +
rowId, null, null, null, null, null);
if (mCursor != null) {
mCursor.moveToFirst();
}
return mCursor;
}
public boolean updateReminder(long rowId, String title, String body, String reminderDateTime) {
ContentValues args = new ContentValues();
args.put(KEY_TITLE, title);
args.put(KEY_BODY, body);
args.put(KEY_DATE_TIME, reminderDateTime);
return mDb.update(DATABASE_TABLE, args, KEY_ROWID + "=" + rowId, null) > 0;
}
// The SQLiteOpenHelper class was omitted for brevity
// That code goes here.
}
雖然我想補充一些意見。我會推出所有'最初'的東西，打開數據庫並統計行數。如果爲0，那麼你的init插入。另外，'初生'是混亂的，因爲你第一次跑，它的錯誤，雖然邏輯會說它應該是真的，對嗎？ –
ohh親愛的，爲什麼我沒看見那！謝謝你，現在工作正常。關於firsttimer，是的，它在第一次運行時是錯誤的，但在創建數據庫後變爲true。由於它現在仍然如此，它不會再次創建數據庫。 –
我的意思是變量名稱沒有意義。你第一次跑步的時候，'初生'是假的，但這個名字意味着它是真的。該代碼將按原樣工作，但我會更改名稱，以免您將自己困在路上。 –