From your question it seems that while your dialog is open you need not to close dialog untill user can select any 1 open from dialog if i am not wrong then,so for this you need not to disable back key but you have to set this two properties for dialog.
dialog.setCancelable(false);
dialog.setCanceledOnTouchOutside(false);
OR
If you want to disable back key then use the below code,
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if (keyCode == KeyEvent.KEYCODE_BACK) {
//preventing default implementation previous to android.os.Build.VERSION_CODES.ECLAIR
return true;
}
return super.onKeyDown(keyCode, event); }
OnbackkeyPressed Requires Api Level 5 Or higher.
@Override
public void onBackPressed() {
}