Question

to prevent user inputs the same data into database i use this

db.execSQL("CREATE UNIQUE INDEX DIFFERENT ON user(name, gender)");

My question is how can i show the error to end users that tell them the data that they input exists already? Or there is another way to prevent the user to input same data and show the error to the user?

DatabaseUsername.java (where i put unique index)

public class DatabaseUsername extends SQLiteOpenHelper {
private static final String DATABASE_NAME="rikartoiy.db";
private static final int SCHEMA_VERSION=1;


public DatabaseUsername(Context context) {
    super(context, DATABASE_NAME, null, SCHEMA_VERSION);
}

@Override
public void onCreate(SQLiteDatabase db) {
    db.execSQL("CREATE TABLE user (_id INTEGER PRIMARY KEY AUTOINCREMENT, name TEXT, gender TEXT);");
    db.execSQL("CREATE TABLE score (_id INTEGER PRIMARY KEY AUTOINCREMENT, score INTEGER, dateTaken TEXT, userId INTEGER NOT NULL, FOREIGN KEY (userId) REFERENCES user(_id) ON DELETE CASCADE);"); //create table score
    db.execSQL("CREATE UNIQUE INDEX DIFFERENT ON user(name, gender)")


}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    // no-op, since will not be called until 2nd schema
    // version exists

}

public Cursor getAll() {
    return(getReadableDatabase()
                    .rawQuery("SELECT _id, name, gender FROM user ORDER BY name",
                                        null));
}

public Cursor getCurScore() {
    return(getReadableDatabase()
                    .rawQuery("SELECT alm._id, alm.name, alm.gender, sc._id, sc.score, sc.userId FROM user alm, score sc WHERE sc.userId = alm._id AND alm._id = ?",
                                        null));
}

public Cursor getById(String id) {
    String[] args={id};

    return(getReadableDatabase()
                    .rawQuery("SELECT _id FROM user WHERE _ID=?",
                                        args)); 
}

public void insert(String name, String gender) {
    ContentValues cv=new ContentValues();

    cv.put("name", name);
    cv.put("gender", gender);

    getWritableDatabase().insert("user", name, cv);
}

public void insertMark(int score, int userId, String dateTaken) {
    ContentValues cv=new ContentValues();

    cv.put("score", score);
    cv.put("userId", userId);
    cv.put("dateTaken", dateTaken);

    getWritableDatabase().insert("score", null, cv);
}

public String getName(Cursor c) {
    return(c.getString(1));
}

public String getGender(Cursor c) {
    return(c.getString(2));
}

public int getScore(Cursor c) {
    return(c.getInt(3));
}}

UsernameRegister.java(where user inputs the data)

public class UsernameRegister extends Activity {
EditText name=null;
RadioGroup gender=null;
DatabaseUsername helper=null;
String almagId=null;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.usernameregister);

    helper=new DatabaseUsername(this);

    name=(EditText)findViewById(R.id.name);
    gender=(RadioGroup)findViewById(R.id.gender);

    Button save=(Button)findViewById(R.id.save);

    save.setOnClickListener(onSave);

    almagId=getIntent().getStringExtra(UsernameList.ID_EXTRA);

    if (almagId!=null) {
        load();
    }
}

@Override
public void onDestroy() {
    super.onDestroy();

    helper.close();
}

private void load() {
    Cursor c=helper.getById(almagId);

    c.moveToFirst();        
    name.setText(helper.getName(c));

    if (helper.getGender(c).equals("Pria")) {
        gender.check(R.id.pria);
    }
    else if (helper.getGender(c).equals("Perempuan")) {
        gender.check(R.id.perempuan);
    }


    c.close();
}

private View.OnClickListener onSave=new View.OnClickListener() {
    public void onClick(View v) {
        String type=null;

        switch (gender.getCheckedRadioButtonId()) {
            case R.id.pria:
                type="Pria";
                break;
            case R.id.perempuan:
                type="Perempuan";
                break;

        }

        String namanama = name.getText().toString();

        if (almagId==null) {
            helper.insert(namanama, type);



            if(TextUtils.isEmpty(namanama)) 
            { 
                name.setError("Your name can't be empty"); 
                return; 
            }

            else if (namanama.length() < 3 ) 
            { 
                name.setError("Your name can't less than 3"); 
                return; 
            }

            else if (namanama.length() > 10 ) 
            { 
                name.setError("Your name can't more than 3"); 
                return; 
            }

        }


        finish();
    }
};}

Answer 1

You can use the return value of mDb.insert();

Returns

    the row ID of the newly inserted row, or -1 if an error occurred 

if it returns -1, AND you are sure that the error could not come from something else than duplicate values, tell the user values already exist.

Or you can create a function that looks for the values entered by user in database, if these values exist, show a message to user before inserting them.