I have created DBAdapter class which is responsible for making a connection to a Database and does any query and finally close the connection.
I have another class which it is not inherited from Activity class(ReminderBeep), but i have to use my DBAdapter in this class.
Actually i don't know how can i manipulate the DBAdapter constructor to make the connection.*
The error is: The constructor DBAdapter(ReminderBeep) is undefined
DBAdapter is:
public class DBAdapter {
static final String DATABASE_NAME = "MyDB";
static final int DATABASE_VERSION = 2;
final Context context;
DatabaseHelper DBHelper;
SQLiteDatabase db;
public DBAdapter(Context ctx)
{
this.context = ctx;
DBHelper = new DatabaseHelper(context);
}
private static class DatabaseHelper extends SQLiteOpenHelper
{
DatabaseHelper(Context context)
{
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
#Override
public void onCreate(SQLiteDatabase db)
{
}
#Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)
{
}
}
//---opens the database---
public DBAdapter open() throws SQLException
{
db = DBHelper.getWritableDatabase();
return this;
}
//---closes the database---
public void close()
{
DBHelper.close();
}
public void insert(String sql)
{
db.execSQL(sql);
}
}
BeepReminder is:
public class ReminderBeep
{
public void DeleteDailyActivities()
{
DBAdapter db=new DBAdapter(this);
db.open();
String sql="delete from DailyWorks";
db.insert(sql);
db.close();
}
}
ReminderBeep is not extendig Activity. But DBAdapter want a Context as paramter,
DBAdapter db=new DBAdapter(this);
this refers to ReminderBeep
Related
I have a class App which extends Application and has a static method which returns context(which is static).
public class App extends Application {
private static Context context;
#Override
public void onCreate() {
super.onCreate();
context = this.getApplicationContext();
DBHelper dbHelper = new DBHelper();
DatabaseManager.initializeInstance(dbHelper);
}
public static Context getContext() {
return context;
}
}
Now in the DBHelper class which extends SQLiteAssetHelper in the constructor, i have this:
public DBHelper() {
super(App.getContext(), DATABASE_NAME, null, DATABASE_VERSION);
}
This is the DataBaseManager class:
public class DatabaseManager {
private Integer mOpenCounter = 0;
private static DatabaseManager instance;
private static SQLiteOpenHelper mDatabaseHelper;
private SQLiteDatabase mDatabase;
public static synchronized void initializeInstance(SQLiteOpenHelper helper) {
if (instance == null) {
instance = new DatabaseManager();
mDatabaseHelper = helper;
}
}
public static synchronized DatabaseManager getInstance() {
if (instance == null) {
throw new IllegalStateException(DatabaseManager.class.getSimpleName() +
" is not initialized, call initializeInstance(..) method first.");
}
return instance;
}
public synchronized SQLiteDatabase openDatabase() {
mOpenCounter+=1;
if(mOpenCounter == 1) {
// Opening new database
mDatabase = mDatabaseHelper.getWritableDatabase();
}
return mDatabase;
}
}
Everything works fine, but there is a design problem because context fields should not be static. How do I use a context in DBHelper while keeping the code working and the field non-static?
You can pass ApplicationContext inside the DBHelper constructor like below:
public DBHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
and then
DBHelper dbHelper = new DBHelper(getApplicationContext());
Could you please help me with error "java.lang.NullPointerException". I use custom listpreference to show elements from database. There two files CustomListPreference.java and DbHelper.java
CustomListPreference.java
public class CustomListPreference extends ListPreference {
CustomListPreferenceAdapter customListPreferenceAdapter = null;
Context mContext;
private SQLiteDatabase db;
DbHelper dbHelp = new DbHelper(mContext);
public CustomListPreference(Context context, AttributeSet attrs)
{
super(context, attrs);
mContext = context;
mInflater = LayoutInflater.from(context);
}
#Override
protected void onPrepareDialogBuilder(Builder builder)
{
...
try {
db = dbHelp.getReadableDatabase();//I get error java.lang.NullPointerException
...
}
DbHelper.java
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class DbHelper extends SQLiteOpenHelper {
static String DATABASE_NAME="myBase";
public static final String KEY_NAME="name";
public static final String KEY_ID="id";
public DbHelper(Context context) {
super(context, DATABASE_NAME, null, 1);
}
#Override
public void onCreate(SQLiteDatabase db) {
db.execSQL("create table tUser ("
+ "id integer primary key autoincrement,"
+ "name text,"
+ "exists integer" + ");");
}
#Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("DROP TABLE IF EXISTS "+TABLE_NAME);
onCreate(db);
}
}
because your mContext is null
place this line inside constructor..or any of your other preferece methods before using it
dbHelp = new DbHelper(context);
Context mContext;
private SQLiteDatabase db;
DbHelper dbHelp = new DbHelper(mContext);
The mContext you passed to DbHelper constructor is null.
You should not initialize any class member requiring a valid Context until onCreate() anyway.
I have a swipeview with two different views(fragments) via a viewpager. I now want these two pages to show different data from an sqllite database. The Problem is i cant figure out how to do this, from the main activity i am not able to access the views (TableLayout) on my fragments and from the fragments sourcecode i cant access the database because the adapter wont open (context of adapter is super.getActivity()). Is there any way to do this?
Code of the Fragment:
DBAdapter adapter = new DBAdapter(getActivity());
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// TODO Auto-generated method stub
if(container==null){
return null;
}
layout=(RelativeLayout)inflater.inflate(R.layout.layout_morning, container, false);
adapter.open();
adapter.close();
Code of DBAdapter:
private static String DB_NAME = "database.dat";
private final Context context;
private DatabaseHelper DBHelper;
private SQLiteDatabase db;
public DBAdapter(Context ctx) {
this.context = ctx;
DBHelper = new DatabaseHelper(context);
}
private static class DatabaseHelper extends SQLiteOpenHelper {
DatabaseHelper(Context context) {
super(context, DB_NAME, null, 1);
}
#Override
public void onCreate(SQLiteDatabase db) {
}
#Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
}
public DBAdapter open() throws SQLException {
db = DBHelper.getWritableDatabase();
return this;
}
public void close() {
if (db!=null){
db.close();
}
DBHelper.close();
}
Error is a NullPointerException
of course you can access a database inside a fragment, you just need to use getActivity(); instead of this.
Example to save an image file inside a fragment class:
db = new DatabaseHandler(getActivity());
ByteArrayOutputStream stream = new ByteArrayOutputStream();
photo.compress(Bitmap.CompressFormat.JPEG, 100, stream);
byte[] imageInByte = stream.toByteArray();
db.updateUser(imageInByte);
db.close();
I'm trying to create table in the sqlite, but it is showing error that table cannot be created. I have a same code but the database and table name are different. the fields are same. Also one doubt. Can't i create the different table in the same database containing the same fields.
DbAdapter.java
the code is as below.
public class DbAdapter {
private static final String DATABASE_NAME="bible1";
private static final String DATABASE_TABLE="test1";
private static final int DATABASE_VERSION=1;
public static final String KEY_ID="_id";
public static final String UNITS="units";
public static final String CHAPTERS="chapters";
private static final String CREATE_DATABASE="create table test1 (_id integer primary key autoincrement, units text not null, chapters text not null);";
private SQLiteHelper sqLiteHelper;
private static SQLiteDatabase sqLiteDatabase;
private Context context;
//constructor
public DbAdapter(Context c){
context = c;
}
private static class SQLiteHelper extends SQLiteOpenHelper{
public SQLiteHelper(Context context){
super(context,DATABASE_NAME,null,DATABASE_VERSION);
}
#Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
db.execSQL(CREATE_DATABASE);
MakeUnits();
}
#Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
}
}
public DbAdapter open() throws SQLException{
try{
sqLiteHelper = new SQLiteHelper(context);
sqLiteDatabase = sqLiteHelper.getWritableDatabase();
}catch(NullPointerException ne){
Log.e("error in creating the table", "bye");
}
return this;
}
public void close(){
sqLiteHelper.close();
}
public static long MakeUnits()
{
ContentValues insert1 = new ContentValues();
insert1.put(UNITS, "Unit1");
insert1.put(CHAPTERS, "CHAPTER1");
return sqLiteDatabase.insert(DATABASE_TABLE,null,insert1);
}
public Cursor fetchAllNotes(){
return sqLiteDatabase.query(DATABASE_TABLE, new String[]{KEY_ID,UNITS,CHAPTERS}, null, null, null, null, null);
}
}
MainActivity.java
public class MainActivity extends ListActivity {
private DbAdapter Database;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ListView listContent = (ListView) findViewById(android.R.id.list);
Database= new DbAdapter(this);
Database.open();
Cursor c = Database.fetchAllNotes();
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.activity_main, menu);
return true;
}
}
It is giving error when the open() method is called. Couldn't figure it out.
in the logcat the error in the tag is that "error in creating the table"
You're trying to call sqLiteDatabase.insert inside MakeUnits, but this sqLiteDatabase variable is null until after you call getWritableDatabase. You should pass db to MakeUnits and call insert on db, not on sqLiteDatabase.
database will be created only when you make a call to
getWritableDatabase()/getReadableDatabase()
If you do not have permissions for a writable db, you will get a readable
db.
public SQLiteDatabase getWritableDB() {
try {
return helper.getWritableDatabase();
} catch (Exception e) {
return getReadableDB();
}
}
public SQLiteDatabase getReadableDB() {
return helper.getReadableDatabase();
}
Hey guys I already have a data in my database but I want to show it into spinner I'm really new to this problem, so would you guys help me to solve this problem,or I would prefer if you write the correct code for me :) Thanks in advance.
First this is my DB class
public class DBAdapter
{
public static final String UPDATEDATE = "UpdateDate";
//Declare fields in PersonInfo
public static final String ROWID = "_id";
public static final String PT_FNAME = "Username";
public static final String PT_COLORDEF = "ColorDeficiency";
private static final String DATABASE_CREATE =
"create table PersonInfo (_id integer primary key autoincrement, "
+ "Username text not null, ColorDeficiency text);";
private static final String DATABASE_NAME = "CAS_DB";
private static final String tbPerson = "PersonInfo";
private static final int DATABASE_VERSION = 1;
private final Context databaseContext;
private final Context context;
private DatabaseHelper DBHelper;
public SQLiteDatabase db;
public DBAdapter(Context ctx)
{
this.context = ctx;
DBHelper = new DatabaseHelper(context);
databaseContext = ctx;
}
//start database helper
private static class DatabaseHelper extends SQLiteOpenHelper
{
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)
{
}
}
//---opens the database---
public DBAdapter open() throws SQLException
{
db = DBHelper.getWritableDatabase();
return this;
}
//---closes the database---
public void close()
{
DBHelper.close();
}
public Cursor all(Activity activity){
String[] from ={ROWID,PT_FNAME,PT_COLORDEF};
String order = PT_FNAME;
Cursor cursor =db.query(tbPerson, from, null, null, null, null, order);
activity.startManagingCursor(cursor);
return cursor;
}
In another class
private DBAdapter db;
private Spinner spinner;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.greeting);
initComponent();
db = new DBAdapter(this);
Cursor c = db.all(this);
SimpleCursorAdapter CursorAdapter = new SimpleCursorAdapter(
this,android.R.layout.simple_spinner_item,c,
new String[]{DBAdapter.PT_FNAME},new int[]{android.R.id.list});
CursorAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spinner.setAdapter(CursorAdapter);
try changing
new int[]{android.R.id.list}
to
new int[]{android.R.layout.simple_spinner_item}