android – AlertDialog没有显示两个按钮

protected Dialog onCreateDialog(int id) {
    final AlertDialog.Builder dialog = new AlertDialog.Builder(this);
    dialog.setMessage("Enter Holla message");
    EditText hollaMessage = new EditText(this);
    dialog.setView(hollaMessage);
    dialog.setCancelable(false);
    dialog.setPositiveButton("Send", new DialogInterface.OnClickListener() {
       public void onClick(DialogInterface dialog, int id) {
          List result = new ArrayList();
       }
    });
    dialog.setPositiveButton("Cancel", new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface dialog, int which) {
            dismissDialog(0);
        }
    });
    AlertDialog alert = dialog.create();
    return alert;
}

protected Dialog onCreateDialog(int id)
{
    final AlertDialog.Builder dialog = new AlertDialog.Builder(this);
    dialog.setMessage("Enter Holla message");
    EditText hollaMessage = new EditText(this);
    dialog.setView(hollaMessage);
    dialog.setCancelable(false);
    dialog.setPositiveButton("Send", new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface dialog, int id) {
            List result = new ArrayList();
        }
    });
    dialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface dialog, int which) {
            dismissDialog(0);
        }
    });
    AlertDialog alert = dialog.create();
    return alert;
}