@Override    public boolean onKeyDown(int keyCode, KeyEvent event) {        if (keyCode == KeyEvent.KEYCODE_BACK) {            new AlertDialog.Builder(this)                    .setIcon(android.R.drawable.ic_menu_info_details)                    .setTitle("退出程序")                    .setMessage("是否要退出？")                    .setPositiveButton("确定",                            new DialogInterface.OnClickListener() {                                @Override                                public void onClick(DialogInterface dialog,                                        int which) {                                    System.exit(0);                                }                            })                    .setNegativeButton("取消",                            new DialogInterface.OnClickListener() {                                @Override                                public void onClick(DialogInterface dialog,                                        int which) {                                }                            }).create().show();        }        return super.onKeyDown(keyCode, event);    }