Android 5.1 怎么修改源码packageinstaller 实现静默安装卸载

如标题所述，哪位大神做过这个需求，求指教怎么在源码上实现静默安装，感激。。。

public class UpdateService extends Service {
/** 安卓系统下载类 **/
DownloadManager manager;

/** 接收下载完的广播 **/
DownloadCompleteReceiver receiver;

/** 初始化下载器 **/
private void initDownManager(String url) {

    manager = (DownloadManager) getSystemService(DOWNLOAD_SERVICE);

    receiver = new DownloadCompleteReceiver();

    //设置下载地址
    DownloadManager.Request down = new DownloadManager.Request(
            Uri.parse(url));

    // 设置允许使用的网络类型，这里是移动网络和wifi都可以
    down.setAllowedNetworkTypes(DownloadManager.Request.NETWORK_MOBILE
            | DownloadManager.Request.NETWORK_WIFI);

    // 下载时，通知栏显示途中
    down.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE);

    // 显示下载界面
    down.setVisibleInDownloadsUi(true);

    // 设置下载后文件存放的位置
    down.setDestinationInExternalFilesDir(this,
            Environment.DIRECTORY_DOWNLOADS, "xiaozhuol.apk");

    // 将下载请求放入队列
    manager.enqueue(down);

    //注册下载广播
    registerReceiver(receiver, new IntentFilter(
            DownloadManager.ACTION_DOWNLOAD_COMPLETE));
}

@Override
public int onStartCommand(Intent intent, int flags, int startId) {
    if (intent.getExtras() != null){
        Bundle bundle = intent.getExtras() ;
        String url = bundle.getString("url") ;
        // 调用下载
        initDownManager(url);
    }


    return super.onStartCommand(intent, flags, startId);
}

@Override
public IBinder onBind(Intent intent) {

    return null;
}

@Override
public void onDestroy() {

    // 注销下载广播
    if (receiver != null)
        unregisterReceiver(receiver);

    super.onDestroy();
}

// 接受下载完成后的intent
class DownloadCompleteReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {

        //判断是否下载完成的广播
        if (intent.getAction().equals(
                DownloadManager.ACTION_DOWNLOAD_COMPLETE)) {

            //获取下载的文件id
            long downId = intent.getLongExtra(
                    DownloadManager.EXTRA_DOWNLOAD_ID, -1);

            //自动安装apk
            installAPK(manager.getUriForDownloadedFile(downId));

            //停止服务并关闭广播
            UpdateService.this.stopSelf();

        }
    }

    /**
     * 安装apk文件
     */
    private void installAPK(Uri apk) {

        // 通过Intent安装APK文件
        Intent intents = new Intent();

        intents.setAction("android.intent.action.VIEW");
        intents.addCategory("android.intent.category.DEFAULT");
        intents.setDataAndType(apk,"application/vnd.android.package-archive");
        intents.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        // 如果不加上这句的话在apk安装完成之后点击单开会崩溃

        getApplication().startActivity(intents);
        android.os.Process.killProcess(android.os.Process.myPid());
    }

}

}