无法从其他类调用函数

Question

I'm creating an app on Android studio using java and a SQLite database. I have created a function to get data from the database in a list but i am not able to call it from an other class.

public List getNumTicket(){
    List NumTicket=new ArrayList();
    SQLiteDatabase db = this.getWritableDatabase();
    String query = "SELECT nbTicket FROM TicketCaisse";
    Cursor cursor = db.rawQuery(query, null);
    while(cursor.moveToNext()){
        NumTicket.add(cursor.getInt(0));
    }
    db.close();
    return NumTicket;
}

This function is in a class which is using SQLiteOpenHelper

public class BaseSQLite extends SQLiteOpenHelper{

public BaseSQLite(Context context, String name, SQLiteDatabase.CursorFactory factory, int version)
{
    super(context,name,factory,version);
}

And i'm trying to call it from the class "accueil"

public class Accueil extends AppCompatActivity {

I would be very happy if you could help me on this one . If you need more infos ask me ;)

Answer 1

public class Accueil extends AppCompatActivity {
oncreate{
BaseSQLite bsqlite = new BaseSQLite(//pass constructors what you are need);
bsqlite.getNumTicket();

Answer 2

The function belongs to the BaseSQLite class thus you need to instiantiate (create) a BaseSQlite object which uses the class constructor.

The class constructor is the following :-

public BaseSQLite(Context context, String name, SQLiteDatabase.CursorFactory factory, int version)
{
    super(context,name,factory,version);
}

So you need to have code such as

    BaseSQLite name_of the_object = new BaseSQLite(
        context_to_be_used,
        Database_name,
        cursor_factory, // null will very likely suit
        version
    );

Once you have the object ( name_of_the object if the above were used) you can then use it's methods (functions) so name_of_object.getNumTicket() will invoke the method(function).

More specifically :-

---

In Accueil 's onCreate method after the setContentView line have :-

  BaseSQLite mybasesqlite = new BaseSQLite(this,"your_database_name",null,1); List mylist = mybasesqlite.getNumTicket(); 

---

Notes

• typically you'd have the database name null and version hard coded in the constrcutor, so you'd then only need to use BaseSQLite mybasesqlite = new BaseSQLite(this);

• eg The If the database were mydatabase.d b and the version were 1 then you could have :-

  public BaseSQLite(Context context) { super(context,"mydatabase.db",null,1); }

• null for the cursor factory is very likely fine at this stage.

---

However, I'd suggest having a single occurrence (constant), of the database name, version table names and columns and always refer to that eg

public class BaseSQLite extends SQLiteOpenHelper{

    public static final String DBNAME = "mydatabase.db";
    public static final int DBVERSION = 1;
    public static final String TB_TICKETCAISSE = "TicketCaisse";
    public static final String COL_TICKETCAISSE_NBTICKET = "nbTicket"

    public BaseSQLite(Context context) {
        super(context,DBNAME,null,DBVERSION);
    }
    ......
    public List getNumTicket(){
        List NumTicket=new ArrayList();
        SQLiteDatabase db = this.getWritableDatabase();
        String query = "SELECT " + COL_TICKETCAISSE_NBTICKET + " FROM " + TB_TICKETCAISSE;
        Cursor cursor = db.rawQuery(query, null);
        while(cursor.moveToNext()){
            NumTicket.add(cursor.getInt(csr.getColumnIndex(COL_TICKETCAISSE_NBTICKET)));
        }
        cursor.close() //<<<< ADDED should always close Cursors when done with them
        db.close();
        return NumTicket;
}

The corresponding Activity could be along the lines of :-

public class Accueil extends AppCompatActivity {

    BaseSQLite  mybasesqlite;      

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mybasesqlite = new BaseSQLite(this);
        List mylist = mybasesqlite.getNumTicket();

    }
    // if used in another method then
    private void doSomethingElse() {
        List myotherlist = mybasesqlite.getNumTicket();
    }
}

Answer 3

Create BaseSQLite.class object

public List getNumTicket(){
    List NumTicket=new ArrayList();
    BaseSQLite db = this.getWritableDatabase();
    String query = "SELECT nbTicket FROM TicketCaisse";
    Cursor cursor = db.rawQuery(query, null);
    while(cursor.moveToNext())
      {
      NumTicket.add(cursor.getInt(0));
      }
    db.close();
    return NumTicket;
}