如何让AlertDialog 在点击确定或者取消时不消失

http://hi.baidu.com/doyee/item/5e27c1155df589dcbf904246

        new AlertDialog.Builder(activity)
                .setView(view)
                .setCancelable(false)
                .setTitle("登陆系统")
                .setPositiveButton("登录", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int i) {
                        EditText userName = (EditText) view.findViewById(R.id.editText);
                        EditText userpwd = (EditText) view.findViewById(R.id.editText1);
                        try {
                            if (userName == null || userName.getText().toString().trim().length() == 0) {
                                //不关闭对话框
                                Field field = dialog.getClass().getSuperclass().getDeclaredField("mShowing");
                                field.setAccessible(true);
                                field.set(dialog, false);   //设定为false,则不可以关闭对话框
                                dialog.dismiss();
                                ToastUtils.show(activity, "没有输入用户名......");
                            } else if (userpwd == null || userpwd.getText().toString().trim().length() == 0) {
                                //不关闭对话框
                                Field field = dialog.getClass().getSuperclass().getDeclaredField("mShowing");
                                field.setAccessible(true);
                                field.set(dialog, false);      //设定为false,则不可以关闭对话框
                                dialog.dismiss();
                                ToastUtils.show(activity, "没有输入密码......");
                            } else {
                                // 要正常关闭对话框
                                ToastUtils.show(activity, "登陆成功......");
                                Field field = dialog.getClass().getSuperclass().getDeclaredField("mShowing");
                                field.setAccessible(true);
                                field.set(dialog, true);//设定为true,则可以关闭对话框
                                dialog.dismiss();

                            }
                        } catch (Exception e) {

                        }


                    }
                })
                .setNegativeButton("取消", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialogInterface, int i) {
                        activity.finish();
                    }
                }
                )
                .create()
                .show();

可以关闭：
field.setAccessible(true);
field.set(dialog, true);//设定为true,则可以关闭对话框/color]

禁止关闭：
[color=darkblue]field.setAccessible(true);
field.set(dialog, false);      //设定为false,则不可以关闭对话框