Vfrdtyky

I found the following thread Check whether database is empty . But the solution given does not seem to work for me. Can someone please give me a hint of how to proceed? I'm new to SQlite and Android studio. Thanks

This is what I'm trying to do.

public class MainActivity extends AppCompatActivity {

    public static boolean firstOrNot = false;

    static User user;

    MyDBHandler myDb;

    @Override



    protected void onCreate(Bundle savedInstanceState) {

        myDb = new MyDBHandler(this);

I initialize my Database variable.

myProgressBtn.setOnClickListener(new View.OnClickListener() {

            @Override

            public void onClick(View v) {



            if(myDb.isNotEmpty() != true) 

Below here is where the problem arises. When I call this method it seems to completely freeze my program. I want it to return a boolean to see if the database is empty or not. This is how the method looks

public boolean isNotEmpty(){

    SQLiteDatabase db = this.getWritableDatabase();



    Cursor mCursor = db.rawQuery("SELECT * FROM " + TABLE_NAME, null);

    Boolean rowExists;



    if (mCursor.moveToFirst())

    {

        // DO SOMETHING WITH CURSOR

        rowExists = true;



    } else

    {

        // I AM EMPTY

        rowExists = false;

    }



    return rowExists;

}

This is how the rest of MyDBHandler class looks like.

package com.example.marko.lektion2;



import android.database.DatabaseErrorHandler;

import android.database.sqlite.SQLiteDatabase;

import android.database.sqlite.SQLiteOpenHelper;

import android.content.Context;

import android.content.ContentValues;

import android.database.Cursor;

import android.util.Log;





public class MyDBHandler extends  SQLiteOpenHelper{



    private static final String TAG = "DatabaseHelper";





    public static final String TABLE_NAME  ="REGISTRATION";

    public static final String COLUMN_ID = "ID";

    public static final String COLUMN_WEIGHT = "WEIGHT";

    public static final String COLUMN_AGE = "AGE";

    private static final String COLUMNS = { COLUMN_ID, COLUMN_WEIGHT, COLUMN_AGE};





    public MyDBHandler(Context context ) {

        super(context, TABLE_NAME, null , 1);

      //  SQLiteDatabase db = this.getWritableDatabase();

    }







    @Override

    public void onCreate(SQLiteDatabase db) {

        String createTable = "CREATE TABLE USER (" +  "id INTEGER PRIMARY KEY AUTOINCREMENT ," +

                "weight INTEGER ," + " age INTEGER)  ";

            db.execSQL(createTable);



    }



    @Override

    public void onUpgrade(SQLiteDatabase db, int i, int i1) {

        db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);

        onCreate(db);

    }





    public User getUser(int id) {

        SQLiteDatabase db = this.getReadableDatabase();

        Cursor cursor = db.query(TABLE_NAME, // a. table

                COLUMNS, // b. column names

                " id = ?", // c. selections

                new String { String.valueOf(id) }, // d. selections args

                null, // e. group by

                null, // f. having

                null, // g. order by

                null); // h. limit



        if (cursor != null)

            cursor.moveToFirst();



        User user = new User();

        user.setId(Integer.parseInt(cursor.getString(0)));

        user.setWeight (Integer.parseInt(cursor.getString(1)));

        user.setAge(Integer.parseInt(cursor.getString(2)));



        return user;

    }





    public void addUser(User player) {

        SQLiteDatabase db = this.getWritableDatabase();

        ContentValues values = new ContentValues();

        values.put(COLUMN_WEIGHT, player.getWeight());

        values.put(COLUMN_AGE, player.getAge());

        // insert

        db.insert(TABLE_NAME,null, values);

        db.close();

    }

In your MyDBHandler class this line:

public static final String TABLE_NAME  ="REGISTRATION";

and this:

String createTable = "CREATE TABLE USER (" +  "id INTEGER PRIMARY KEY AUTOINCREMENT ," + "weight INTEGER ," + " age INTEGER)  ";

db.execSQL(createTable);

conflict.

What is the name of your table?

REGISTRATION or USER?

In your method isNotEmpty() you use TABLE_NAME which is REGISTRATION but you have created a table named USER.


Make up your mind about the name of the table, make the change in your code,
uninstall the app from the device/emulator so the database is deleted and rerun to recreate the database.
Repopulate the table and then try again your code.

There are quite a few problems here

1.) don't do database query on UI thread

2.) you can easily reduce the amount of time this call takes with

Cursor mCursor = db.rawQuery("SELECT * FROM " + TABLE_NAME + " LIMIT 1", null);

3.) Don't call it mCursor if it is not a member field, just call it cursor

4.) You are not closing that cursor, you should be closing it in a finally { block at the end.

Cursor cursor = null;

try {

    cursor = db.rawQuery("SELECT * FROM " + TABLE_NAME + " LIMIT 1", null);

    ...

} finally {

    if(cursor != null) {

        cursor.close();

    }

}

I'm pretty sure there is a lint check for this, too.