Cannot resolve symbol for SQlite dbhandler class

Question

I'm trying to create/access SQLite database in android. I've created a file called MDbHandler.java where I've written code to create database, insert,update and delete. Now in the activity where this database need to be used, I'm creating an object under onCreate() method. But in Android Studio 0.8, I'm getting error that "mDbHandler" symbol cannot resolve. What could be the solution?

mDbHandler.java file:

package com.example.smashingwheels;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.provider.BaseColumns;

public class mileageDbHandler extends SQLiteOpenHelper {
    public static final String TABLE_MILEAGE = "mileage";
    public static final String COL_ID = BaseColumns._ID;
    public static final String COL_DATE = "date";
    public static final String COL_LTR = "ltr";
    public static final String COL_ODO = "odo";
    private static final String DATABASE_NAME = "mileageDb";
    private static final int DATABASE_VERSION = 1;

    public mileageDbHandler(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("CREATE TABLE " + TABLE_MILEAGE + " ("
                + COL_ID + " INTEGER PRIMARY KEY AUTOINCREMENT,"
                + COL_DATE + " TEXT NOT NULL,"
                + COL_LTR + " INTEGER,"
                + COL_ODO + " INTEGER"
                + ");");
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_MILEAGE + ";");
        onCreate(db);
    }

    public long insert(String tableName, ContentValues values) throws NotValidException {
        validate(values);

        return getWritableDatabase().insert(tableName, null, values);
    }

    public int update(String tableName, long id, ContentValues values) throws NotValidException {
        validate(values);

        String selection = COL_ID + " = ?";
        String[] selectionArgs = {String.valueOf(id)};

        return getWritableDatabase().update(tableName, values, selection, selectionArgs);
    }

    public int delete(String tableName, long id) {
        String selection = COL_ID + " = ?";
        String[] selectionArgs = {String.valueOf(id)};

        return getWritableDatabase().delete(tableName, selection, selectionArgs);
    }

    protected void validate(ContentValues values) throws NotValidException {
        if (!values.containsKey(COL_DATE) || values.getAsString(COL_DATE) == null || values.getAsString(COL_DATE).isEmpty()) {
            throw new NotValidException("Please enter a valid date.");
        }
    }

    public Cursor query(String tableName, String orderedBy) {
        String[] projection = {COL_ID, COL_DATE, COL_LTR, COL_ODO};
        return getReadableDatabase().query(tableName, projection, null, null, null, null, orderedBy);
    }

    public static class NotValidException extends Throwable {
        public NotValidException(String msg) {
            super(msg);
        }
    }
}

mActivity file:

package com.example.user.smashingwheels;

import android.app.Activity;
import android.content.ContentValues;
import android.content.Intent;
import android.database.Cursor;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.ListView;
import android.widget.SimpleCursorAdapter;
import android.widget.Toast;

import com.example.user.smashingwheels.R;

public class mileagecal extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_mileagecal);

        getActionBar().setHomeButtonEnabled(true);
        getActionBar().setDisplayHomeAsUpEnabled(true);
        getActionBar().setDisplayShowHomeEnabled(false);

        mileageDbHandler mDatabaseHelper = new mileageDbHandler(this);


        addUser("12/5/14", 2, 4500);

    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.mileagecal, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }


        onBackPressed();
        return super.onOptionsItemSelected(item);
    }

    private void addUser(String date, int ltr, int odo) {
        ContentValues values = new ContentValues();
        values.put(mileageDbHandler.COL_DATE, date);

        values.put(mileageDbHandler.COL_LTR, ltr);

        values.put(mileageDbHandler.COL_ODO, odo);

        try {
            mDatabaseHelper.insert(mileageDbHandler.TABLE_USERS, values);
        } catch (mileageDbHandler.NotValidException e) {
            Toast.makeText(this, e.getMessage(), Toast.LENGTH_SHORT).show();
        }
    }
}

Both files are located in src/java/com folder Please help!

Answer 1

Do this

Before OnCreate() Method of mileagecal actvity add this

mileageDbHandler mDatabaseHelper;

so that mDatabaseHelper can be accessible to all methods in this activity

just like this

public class mileagecal extends Activity {

mileageDbHandler mDatabaseHelper; //add this here

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_mileagecal);

    getActionBar().setHomeButtonEnabled(true);
    getActionBar().setDisplayHomeAsUpEnabled(true);
    getActionBar().setDisplayShowHomeEnabled(false);

    //make an object of that class here
    mDatabaseHelper = new mileageDbHandler(this);


    addUser("12/5/14", 2, 4500);

}

Answer 2

Like i stated in my comment the mDbHandler won't be visible to addUser().So u can either create a class level variable i.e

public class mileagecal extends Activity {

mileageDbHandler mDatabaseHelper;

and the use this variable. Or modify ur addUser()

private void addUser(String date, int ltr, int odo,mileageDbHandler mDatabaseHelper)

and replace the addUser("12/5/14", 2, 4500); with addUser("12/5/14", 2, 4500,mDatabaseHelper); in ur onCreate()

Answer 3

package com.casper.pp1.Database;
import android.content.ContentValues;
import android.content.Context;
import android.content.Intent;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import com.casper.pp1.UserModal;
import com.casper.pp1.Userprofile;
import java.util.ArrayList;
import java.util.List;

public class DatabaseHelper extends SQLiteOpenHelper {

    private static final String CREATE_USERINFO_TABLE =
         "CREATE TABLE "+Userprofile.Users.TABLE_NAME+ "("
            +Userprofile.Users.COLUMN_ID+" INT PRIMARY KEY,"
            +Userprofile.Users.COLUMN_USERNAME+" TEXT,"
            +Userprofile.Users.COLUMN_PASSWORD+" TEXT,"
            +Userprofile.Users.COLUMN_DATEOFBIRTH+" TEXT,"
            +Userprofile.Users.COLUMN_GENDER+" TEXT)";
    public static final String DELETE_USERINFO_TABLE=
       "DROP TABLE IF EXISTS "+Userprofile.Users.TABLE_NAME;

    public DatabaseHelper(Context context) {
        super(context, "casper", null, 1);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(CREATE_USERINFO_TABLE);

    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) 
   {
        db.execSQL(DELETE_USERINFO_TABLE);
        onCreate(db);
    }

    public boolean addInfo(String username, String password,
                 String dateofbirth, String gender){
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues values= new ContentValues();
        values.put(Userprofile.Users.COLUMN_USERNAME,username);
        values.put(Userprofile.Users.COLUMN_PASSWORD,password);
        values.put(Userprofile.Users.COLUMN_DATEOFBIRTH,dateofbirth);
        values.put(Userprofile.Users.COLUMN_GENDER,gender);

        long count=db.insert(Userprofile.Users.TABLE_NAME, null, values);
        return count>=0;

    }

    public boolean updateInfo(String username,
           String password, String dateofbirth, String gender){
        int id = getIdByUsername(username);
        SQLiteDatabase db=this.getWritableDatabase();
        ContentValues values= new ContentValues();
        values.put(Userprofile.Users.COLUMN_USERNAME,username);
        values.put(Userprofile.Users.COLUMN_PASSWORD,password);
        values.put(Userprofile.Users.COLUMN_DATEOFBIRTH,dateofbirth);
        values.put(Userprofile.Users.COLUMN_GENDER,gender);

        String selection=Userprofile.Users.COLUMN_ID+" = ?";
        String[] selectionArgs = {Integer.toString(id)};

        long result=db.update(Userprofile.Users.TABLE_NAME,
             values,selection, selectionArgs);
         return result>0;
    }

    public List<UserModal> readAllInfo(){

        SQLiteDatabase db=this.getReadableDatabase();
        List<UserModal> list = new ArrayList<>();

        String sql = "SELECT * FROM "+Userprofile.Users.TABLE_NAME;

        Cursor rs = db.rawQuery(sql,null);

        if (rs.getCount()==0){
            return list;
        }else {
            while (rs.moveToNext()){
                list.add(new UserModal(rs.getInt(0),rs.getString(1),
                        rs.getString(2),rs.getString(3),rs.getString(4)));
            }
            return list;
        }
    }
    public UserModal readAllInfo(String username){

        int id = getIdByUsername(username);
        SQLiteDatabase db=this.getReadableDatabase();
       UserModal user = null;

        String selection=Userprofile.Users.COLUMN_ID+" = ?";
        String[] selectionArgs = {Integer.toString(id)};

        Cursor rs = db.query(Userprofile.Users.TABLE_NAME,
           null,selection,selectionArgs,null,null,null);

        if (rs.getCount()==0){
            return user;
        }else {
            while (rs.moveToNext()){
                user = new UserModal(rs.getInt(0),rs.getString(1),
                        rs.getString(2),rs.getString(3),rs.getString(4));
            }
            return user;
        }
    }

    public boolean deleteInfo(String username){
        int id = getIdByUsername(username);
        SQLiteDatabase db=this.getWritableDatabase();

        String selection=Userprofile.Users.COLUMN_ID+" = ?";
        String[] selectionArgs = {Integer.toString(id)};

        int count = db.delete(Userprofile.Users.TABLE_NAME,
            selection,selectionArgs);
        return count>0;

    }

    public int getIdByUsername(String username){

        SQLiteDatabase db=this.getReadableDatabase();
        UserModal user = null;

        String selection=Userprofile.Users.COLUMN_USERNAME+" LIKE ?";
        String[] selectionArgs = {username};
        int id = -1;



        Cursor rs = db.query(Userprofile.Users.TABLE_NAME,
             null,selection,selectionArgs,null,null,null);

        if (rs.getCount()==0){
            return id;
        }else {
            while (rs.moveToNext()){
                id=rs.getInt(0);
            }
            return id;
        }

    }

}


//********************Home Activity**********************************

public class Home extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_home);
}


public void onClickRegister(View view){
    Intent intent=new Intent(this,ProfileManagement.class);
    startActivity(intent);
}
}


//******************************Profile Management*********************

public class ProfileManagement extends AppCompatActivity {

EditText userName,password,dob;
RadioGroup gender;
RadioButton x;
DatabaseHelper db;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_profile_management);
    db= new DatabaseHelper(this);
    userName = findViewById(R.id.uname_edit);
    password = findViewById(R.id.pass_e22);
    dob = findViewById(R.id.dob_mg);
    gender=findViewById(R.id.gender_mg);
}
public void onClickUpdateProfile(View view){
    int id=gender.getCheckedRadioButtonId();
    x=findViewById(id);



  if(db.addInfo(userName.getText().toString(),
   password.getText().toString(),dob.getText().toString(),
     x.getText().toString())){
        Toast.makeText(this,"successfully registered",
        Toast.LENGTH_SHORT).show();
    }
    else {
        Toast.makeText(this,"not registered",Toast.LENGTH_SHORT).show();
    }
    Intent intent = new Intent(this,EditProfile.class);
    startActivity(intent);
}
}


//*********************************Edit Profile**************************

public class EditProfile extends AppCompatActivity {
  EditText userName,password,dob;
  RadioGroup gender;
  RadioButton x, male,female;
  DatabaseHelper db;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_edit_profile);
    db= new DatabaseHelper(this);
    userName = findViewById(R.id.uname_edit);
    password = findViewById(R.id.pass_e22);
    dob = findViewById(R.id.dob_edit);
    gender=findViewById(R.id.gender_edit);
    male = findViewById(R.id.male_edit);
    female = findViewById(R.id.female_edit);
}
public void OnClickSearch(View view){
    UserModal user;
    user=db.readAllInfo(userName.getText().toString());
    password.setText(user.getPassword());
    dob.setText(user.getDateOfBirth());
    if(user.getGender().equals("Male")){
        male.setChecked(true);
    }else{
        female.setChecked(true);
    }}
public void OnclickEdit(View view){
    int id=gender.getCheckedRadioButtonId();
    x=findViewById(id);


if(db.updateInfo(userName.getText().toString(),
password.getText().toString(),dob.getText().toString(),
x.getText().toString()
    )){
        Toast.makeText(this,"Successfully updated",
       Toast.LENGTH_SHORT).show();
    }else {
        }    }

public void deleteEdit(View view){
    if(db.deleteInfo(userName.getText().toString())){
        //toast
    }
}
}


//*****************************UserProfile*****************************

public final class Userprofile {
private Userprofile(){}

public final static class Users implements BaseColumns {
    public static final String TABLE_NAME = "UserInfo";
    public static final String  COLUMN_ID=BaseColumns._ID;
    public static final String COLUMN_USERNAME="Username";
    public static final String COLUMN_PASSWORD="Password";
    public static final String COLUMN_DATEOFBIRTH="Dateofbirth";
    public static final String  COLUMN_GENDER="Gender";


}

}

Answer 4

public class DBHandler extends SQLiteOpenHelper {

public static final String DataBase="DataBase.db";
public static final String Table_Name="UserInfo";
public static final String col1="id";
public static final String col2="name";
public static final String col3="dob";
public static final String col4="password";
public static final String col5="gender";



public DBHandler(Context context) {
    super(context,DataBase , null, 1);


}

@Override
public void onCreate(SQLiteDatabase sqLiteDatabase) {
        sqLiteDatabase.execSQL("create table "+Table_Name+"("+col1+" integer primary key autoincrement ,"+col2+" text,"+col3+" text ,"+col4+" text ,"+col5+" text )");



}

@Override
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {
    sqLiteDatabase.execSQL("drop table if exists "+Table_Name);
    onCreate(sqLiteDatabase);



}
public boolean AddInfo(String name,String dob,String password,String gender){
    SQLiteDatabase sqLiteDatabase=this.getWritableDatabase();
    ContentValues val=new ContentValues();

    val.put(col2,name);
    val.put(col3,dob);
    val.put(col4,password);
    val.put(col5,gender);

    int i=(int)sqLiteDatabase.insert(Table_Name,null,val);

    if(i>0){
        return true;
    }
    else{
        return false;
    }


}
public boolean updateInfo(String name,String dob,String password,String gender){
    SQLiteDatabase sqLiteDatabase=this.getWritableDatabase();
    ContentValues val=new ContentValues();

    val.put(col2,name);
    val.put(col3,dob);
    val.put(col4,password);
    val.put(col5,gender);

    int i=sqLiteDatabase.update(Table_Name,val,"name="+name,null);
    if(i>0){
        return true;
    }
    else{
        return false;
    }



}
public Cursor readAllInfor(){
    SQLiteDatabase sqLiteDatabase=this.getWritableDatabase();
    Cursor c=sqLiteDatabase.rawQuery("select*from "+Table_Name,null);

    return c;
}

public Cursor readAllInfor(String name){
    SQLiteDatabase sqLiteDatabase=this.getWritableDatabase();
    Cursor c= sqLiteDatabase.rawQuery("select * from "+Table_Name+" where "+col2 +"=\""+name+"\"",null);
    return c;

}

public boolean deleteInfo(String name){

    SQLiteDatabase sqLiteDatabase=this.getWritableDatabase();
    int i=sqLiteDatabase.delete(Table_Name,"name="+name,null);
    if(i>0){
        return true;
    }
    else{
        return false;
    }

}

}

Answer 5

public class DBHandler extends SQLiteOpenHelper {

public static final String DataBase="DataBase.db";
public static final String Table_Name="UserInfo";
public static final String col1="id";
public static final String col2="name";
public static final String col3="dob";
public static final String col4="password";
public static final String col5="gender";



public DBHandler(Context context) {
    super(context,DataBase , null, 1);


}

@Override
public void onCreate(SQLiteDatabase sqLiteDatabase) {
        sqLiteDatabase.execSQL("create table "+Table_Name+"("+col1+" integer primary key autoincrement ,"+col2+" text,"+col3+" text ,"+col4+" text ,"+col5+" text )");



}

@Override
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {
    sqLiteDatabase.execSQL("drop table if exists "+Table_Name);
    onCreate(sqLiteDatabase);



}
public boolean AddInfo(String name,String dob,String password,String gender){
    SQLiteDatabase sqLiteDatabase=this.getWritableDatabase();
    ContentValues val=new ContentValues();

    val.put(col2,name);
    val.put(col3,dob);
    val.put(col4,password);
    val.put(col5,gender);

    int i=(int)sqLiteDatabase.insert(Table_Name,null,val);

    if(i>0){
        return true;
    }
    else{
        return false;
    }


}
public boolean updateInfo(String name,String dob,String password,String gender){
    SQLiteDatabase sqLiteDatabase=this.getWritableDatabase();
    ContentValues val=new ContentValues();

    val.put(col2,name);
    val.put(col3,dob);
    val.put(col4,password);
    val.put(col5,gender);

    int i=sqLiteDatabase.update(Table_Name,val,"name="+name,null);
    if(i>0){
        return true;
    }
    else{
        return false;
    }



}
public Cursor readAllInfor(){
    SQLiteDatabase sqLiteDatabase=this.getWritableDatabase();
    Cursor c=sqLiteDatabase.rawQuery("select*from "+Table_Name,null);

    return c;
}

public Cursor readAllInfor(String name){
    SQLiteDatabase sqLiteDatabase=this.getWritableDatabase();
    Cursor c= sqLiteDatabase.rawQuery("select * from "+Table_Name+" where "+col2 +"=\""+name+"\"",null);
    return c;

}

public boolean deleteInfo(String name){

    SQLiteDatabase sqLiteDatabase=this.getWritableDatabase();
    int i=sqLiteDatabase.delete(Table_Name,"name="+name,null);
    if(i>0){
        return true;
    }
    else{
        return false;
    }

}

}