When I click menuItems in ActionBar, Dialog drops quickly.

@Override
public boolean onOptionsItemSelected(MenuItem){
    switch(item.getItemId()){

        // Since the transition destination is a fragment, write in FragmentTransaction.
        case R.id.menu_home:
            FragmentTransaction ft = getFragmentManager().beginTransaction();
            ft.replace(R.id.container, newTop());
            break;

        case R.id.menu_dialog:
            AlertDialogFragment alertDialog=new AlertDialogFragment();
            alertDialog.show(getFragmentManager(), "AlertDialogFragment";
            break;
    }
    finish();
    return super.onOptionsItemSelected(item);}

public class AlertDialogFragment extensions DialogFragment{
@ Override
public Dialog onCreateDialog (Bundle SavedInstanceState) {
    AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
    builder.setTitle("Title");
    builder.setMessage("message");
    builder.setPositiveButton(R.string.ok, null);
    builder.setNegotisticalButton(R.string.cancel, null);
    return builder.create();
} }