Android - Custom Dialog throws NullPointerException when more than one button is defined

Here's the code that defines my custom dialog. When I show this dialog, it throws a NullPointerException at the commented line.

    protected Dialog onCreateDialog (int id) {
    Dialog dialog = null;
        switch (id) {
        case DIALOG_SUCCESS_ID:

            Context thisContext = this;

            dialog = new Dialog(thisContext);

            dialog.setContentView(R.layout.win_dialog);
            dialog.setTitle("Stage One");

            TextView timeScore = (TextView) dialog.findViewById(R.id.TimeScore);
            timeScore.setText (elapsedTimeSec + "s");
            TextView bestScore = (TextView) dialog.findViewById(R.id.BestScore);
            bestScore.setText ("Best Score: (n/a)");

            Button retry = (Button) dialog.findViewById(R.id.Retry);
            retry.setOnClickListener(new View.OnClickListener() {
                public void onClick (View v) {
                    Intent retry = new Intent(v.getContext(), LevelOne.class);
                    sta开发者_StackOverflow中文版rtActivityForResult(retry, 0);
                    finish();
                }
            });

            Button menu = (Button) dialog.findViewById (R.id.ReturnToMenu);

            //Throws NullPointerException at this line
            menu.setOnClickListener(new View.OnClickListener() {
                public void onClick (View v) {
                    Intent menu = new Intent(v.getContext(), Menu.class);
                    startActivityForResult(menu, 0);
                    finish();
                }
            });
            break;
        case DIALOG_GAMEOVER_ID:
            break;
        default:
            dialog = null;
        }
        return dialog;
}

But when I remove my menu button and the menu.SetOnClickListener() method, it works fine! My retry button also works without a hitch. Why can't I add more than one button? Why does it throw the exception?

It looks like dialog.findViewById (R.id.ReturnToMenu); is returning null. Can you check that you actually have a button with the correct ID? I'd guess that there is a typo somewhere in your "return to menu" button ID.