Can't delete row of recyclerView

i've just starting to develop for android and I got a problem by deleting data from my sqLite Database and updating my RecyclerView properly.

When the user tap on of the rows, he gets a new Activity where he can delete the row via a button.

Here is the Code for my MainActivity

public class MainActivity extends ActionBarActivity implements OnItemClickListener {

private Toolbar toolbar;
private RecyclerView markList;
private MainMarkAdapter adapter;
private DataBase dataBase;
ActionButton actionButton;



View.OnClickListener actionButtonListener = new View.OnClickListener() {

    @Override
    public void onClick(View v) {

        Intent addMarkIntent = new Intent(MainActivity.this, CreateMarkActivity.class);
        //transfer Data to CreateMarkActivity
        //addMarkIntent.putExtra("key", value);
        MainActivity.this.startActivityForResult(addMarkIntent, 1);

    }
};


View.OnClickListener showDetailListener = new View.OnClickListener() {

    @Override
    public void onClick (View v) {
        String myString = "Zeige Details!";
        Toast.makeText(MainActivity.this, myString, Toast.LENGTH_SHORT).show();
    }
};

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

    dataBase = new DataBase(MainActivity.this);

    try {
        dataBase.open();
    } catch (Exception e) {
        e.printStackTrace();
    }

    //set Toolbar
    toolbar= (Toolbar) findViewById(R.id.app_bar);
    setSupportActionBar(toolbar);
    getSupportActionBar().setDisplayShowTitleEnabled(false);

    //set Font
    TextView avgDescTV = (TextView) findViewById(R.id.main_AverageDescription);
    avgDescTV.setTypeface(EasyFonts.robotoMedium(this));

    TextView avgTV = (TextView) findViewById(R.id.main_Average);
    avgTV.setTypeface(EasyFonts.robotoThin(this));

    //set RecyclerView
    markList = (RecyclerView) findViewById(R.id.main_markList);
    adapter = new MainMarkAdapter(this, dataBase.getDataMark(), this);

    /*
    adapter.setOnItemClickListenerWithPosition(new OnItemClickListener() {
        @Override
        public void onItemClick(View view, int position) {

            Intent intent = new Intent(MainActivity.this, DetailMarkActivity.class);

            //transfer Data to CreateMarkActivity
            intent.putExtra("selectedRow", position);
            MainActivity.this.startActivityForResult(intent, 2);
        }
    });
    */

    markList.setAdapter(adapter);
    markList.setLayoutManager(new LinearLayoutManager(this));

    //set FloatingActionButton
    actionButton = (ActionButton) findViewById(R.id.main_addMark);
    actionButton.setOnClickListener(actionButtonListener);

    //set DetailView
    TextView detailTV = (TextView) findViewById(R.id.main_Average);
    detailTV.setOnClickListener(showDetailListener);
}

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

@Override
protected void onResume() {
    adapter.notifyDataSetChanged();
    try {
        dataBase.open();
    } catch (Exception e) {
        e.printStackTrace();
    }

    actionButton.show();

    super.onResume();
}

@Override
protected void onPause() {
    dataBase.close();

    super.onPause();
}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {

    if (requestCode == 1) {
        if (resultCode == RESULT_OK) {
            try {
                dataBase.open();
            } catch (Exception e) {
                e.printStackTrace();
            }
            markList.setAdapter(new MainMarkAdapter(this, dataBase.getDataMark(), this));
        }
    } else if (requestCode == 2) {
        if (resultCode == RESULT_OK) {
            try {
                dataBase.open();
            } catch (Exception e) {
                e.printStackTrace();
            }

            int selectedIndex = data.getExtras().getInt("index");

            System.out.println(selectedIndex);

            dataBase.getDataMark().remove(selectedIndex);

            markList.setAdapter(new MainMarkAdapter(this, dataBase.getDataMark(), this));

            adapter.notifyItemRemoved(selectedIndex);
            adapter.notifyItemRangeChanged(selectedIndex, dataBase.getDataMark().size());

            dataBase.close();


        }
    }
}

@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();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        Toast.makeText(this, item.getTitle(), Toast.LENGTH_SHORT).show();

        return true;
    } else if (id == R.id.actionStudentID) {
        Toast.makeText(this, item.getTitle(), Toast.LENGTH_SHORT).show();

        return true;
    } else if (id == R.id.actionSubjects) {
        Toast.makeText(this, item.getTitle(), Toast.LENGTH_SHORT).show();

        return true;
    } else if (id == R.id.actionTestTypes) {
        Toast.makeText(this, item.getTitle(), Toast.LENGTH_SHORT).show();

        return true;
    } else if (id == R.id.actionCalculator) {
        Toast.makeText(this, item.getTitle(), Toast.LENGTH_SHORT).show();

        return true;
    } else if (id == R.id.main_addMark) {
        actionButton.hide();
        Toast.makeText(this, "Toastie", Toast.LENGTH_SHORT).show();
    }

    return super.onOptionsItemSelected(item);
}

@Override
public void onItemClick(View view, int position) {
    Intent intent = new Intent(MainActivity.this, DetailMarkActivity.class);

    //transfer Data to CreateMarkActivity
    intent.putExtra("selectedRow", position);
    MainActivity.this.startActivityForResult(intent, 2);
}

}

And here is the code I written for the OnClickListener:

View.OnClickListener clickListener = new View.OnClickListener() {
    @Override
    public void onClick(View v) {

        if (v.getId() == R.id.detailMark_deleteButton) {

            try {
                dataBase.open();
            } catch (Exception e) {
                e.printStackTrace();
            }

            dataBase.deleteMark(selectedIndex);

            dataBase.close();

            Intent deleteReturnIntent = new Intent();
            deleteReturnIntent.putExtra("index", selectedIndex);
            setResult(RESULT_OK, deleteReturnIntent);
            finish();
        }

    }
};

And now the delete-method for my database:

public void deleteMark(int index) {
    database.delete(DATABASE_MARKTABLE, KEY_ROWID + "=" + index, null);
}

So when i tapped the button nothing happened... There are all items inside the recyclerView like before. What did I wrong? Can anyone help me?

Thank you very much!