Android : android intent button with alert dialog

I am working on simple android app where user can go to another activity after clicking a button on alert dialog:

I tried but it always make my app crash.

here is my code:

public class MainActivity extends Activity {

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



        AlertDialog.Builder renameDialog = new AlertDialog.Builder(MainActivity.this);
        renameDialog.setTitle("alert");


        renameDialog.setPositiveButton("OK", new DialogInterface.OnClickListener() {

            public void onClick(DialogInterface arg0, int arg1) {
                launchIntent();
            }
        });

        renameDialog.show();
    }

    private void launchIntent() {
        Intent it = new Intent(MainActivity.this, BActivity.class);
        it.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
        startActivity(it);
    }
}