[英]How to save in SQLitedatabase permanently
I have created a SQLitedatabase and want to store data. 我创建了一个SQLitedatabase,并希望存储数据。 But the data is deleted on each start of the app again, because the "create table" methods are implemented in in the OnCreate-Method of the database.
但是,由于在数据库的OnCreate-Method中实现了“ create table”方法,因此在应用程序的每次启动时都会再次删除数据。
OnCreate of the database: 数据库的OnCreate:
@Override
public void onCreate(SQLiteDatabase db) {
//if (!dbNinjaExists(db)) {
createTables(db);
initNinjas(db);
//}
}
Th initNinjas method contains some Insert SQLs which create the sample data. initNinjas方法包含一些创建示例数据的插入SQL。 I already tried to make an if-decision in the constructor to ask whether there is already a database but this doesnt work.
我已经尝试在构造函数中做出if决策,以询问是否已经有一个数据库,但这不起作用。
private boolean dbNinjaExists(SQLiteDatabase db) {
String query = "SELECT * FROM "+ TABLE_NAME;
Cursor data = db.rawQuery(query,null);
if(data.equals(null)){
return false;
}else{
return true;
}
}
The constructor of the MasterActivity creates the database object and starts with beginning of the app. MasterActivity的构造函数创建数据库对象,并从应用程序的开头开始。 As following:
如下:
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
dbHelper = new DatabaseHelper(this);}
The DatabaseHelper Constructor: DatabaseHelper构造函数:
public DatabaseHelper(Context context){
super(context,TABLE_NAME,null,1);
}
Here is my SQLiteAdapter (DBHelper)Class: 这是我的SQLiteAdapter (DBHelper)类:
Using this this db will be created only once. 使用此数据库将仅创建一次。 You can call this from any method and activity.
您可以从任何方法和活动中调用它。 Make changes according to your requirement.
根据您的要求进行更改。
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;
import java.util.ArrayList;
class SQLiteAdapter {
private static final String DB_NAME = "DATABASE";
private static final String KEY_TABLE = "KEY_TABLE";
private static final int DB_VERSION = 1;
private static final String KEY_ID = "_id";
private static final String KEYWORD = "Keyword";
private static final String COUNT = "COUNT";
private static final String CONTACT_NAMES = "CONTACT_NAMES";
private static final String CONTACT_NUMBERS = "CONTACT_NUMBERS";
//create table MY_DATABASE (ID integer primary key, Content text not null);
private static final String SCRIPT_CREATE_DATABASE =
"create table " + KEY_TABLE + " ("
+ KEY_ID + " integer primary key autoincrement, "
+ KEYWORD + " text, "
+ CONTACT_NAMES + " text, "
+ CONTACT_NUMBERS + " text, "
+ COUNT + " integer);";
private SQLiteHelper sqLiteHelper;
private SQLiteDatabase sqLiteDatabase;
private Context context;
SQLiteAdapter(Context c) {
context = c;
}
private void openToRead() throws android.database.SQLException {
sqLiteHelper = new SQLiteHelper(context, DB_NAME, null, DB_VERSION);
sqLiteDatabase = sqLiteHelper.getReadableDatabase();
}
private void openToWrite() throws android.database.SQLException {
sqLiteHelper = new SQLiteHelper(context, DB_NAME, null, DB_VERSION);
sqLiteDatabase = sqLiteHelper.getWritableDatabase();
}
private void close() {
sqLiteHelper.close();
}
boolean insert(SQLiteAdapter sqLiteAdapter, String keyword, String contact_names, String contact_numbers, int count) {
sqLiteAdapter.openToWrite();
ContentValues contentValues = new ContentValues();
contentValues.put(KEYWORD, keyword);
contentValues.put(CONTACT_NAMES, contact_names);
contentValues.put(CONTACT_NUMBERS, contact_numbers);
contentValues.put(COUNT, count);
sqLiteDatabase.insert(KEY_TABLE, null, contentValues);
sqLiteAdapter.close();
return true;
}
void deleteRow(SQLiteAdapter sqLiteAdapter, String id) {
sqLiteAdapter.openToWrite();
sqLiteDatabase.execSQL("delete from " + KEY_TABLE + " where _id='" + id + "'");
sqLiteAdapter.close();
}
ArrayList<RecordModel> getAllRecords(SQLiteAdapter sqLiteAdapter) {
sqLiteAdapter.openToRead();
ArrayList<RecordModel> listItems = new ArrayList<>();
String[] columns = new String[]{KEY_ID, KEYWORD, CONTACT_NAMES, CONTACT_NUMBERS, COUNT};
Cursor cursor = sqLiteDatabase.query(KEY_TABLE, columns,
null, null, null, null, null);
if (cursor.moveToFirst()) {
do {
RecordModel recordModel = new RecordModel();
recordModel.setCount(cursor.getInt(cursor.getColumnIndex(COUNT)));
recordModel.setId(cursor.getString(cursor.getColumnIndex(KEY_ID)));
recordModel.setKeyword(cursor.getString(cursor.getColumnIndex(KEYWORD)));
recordModel.setContactNames(cursor.getString(cursor.getColumnIndex(CONTACT_NAMES)));
recordModel.setContactNumbers(cursor.getString(cursor.getColumnIndex(CONTACT_NUMBERS)));
listItems.add(recordModel);
} while (cursor.moveToNext());
}
cursor.close();
sqLiteAdapter.close();
return listItems;
}
public class SQLiteHelper extends SQLiteOpenHelper {
SQLiteHelper(Context context, String name,
CursorFactory factory, int version) {
super(context, name, factory, version);
}
@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
db.execSQL(SCRIPT_CREATE_DATABASE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
}
}
}
If this: 如果这:
public DatabaseHelper(Context context){
super(context,TABLE_NAME,null,1);
}
is your constructor, 是你的构造函数
it creates a database with name the value of TABLE_NAME
which is I suppose the name of the table you want to create. 它创建一个名称为
TABLE_NAME
的数据库,我想是您要创建的表的名称。
So change TABLE_NAME
with the database name. 因此,将
TABLE_NAME
更改为数据库名称。
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