android application 的生命周期真几把长

重新进入app时它还在，他还在；

AppDownloadManager appDownloadManager = new AppDownloadManager(App.getInstance());

appDownloadManager.downloadApk(UpApkUrl, "sraum正在下载", apkName);

    public AppDownloadManager(Context context) {
//        activity = (Activity) context;
        weakReference = new WeakReference<Context>(context);
        mDownloadManager = (DownloadManager) weakReference.get().getSystemService(Context.DOWNLOAD_SERVICE);
        mDownLoadChangeObserver = new DownloadChangeObserver(new Handler());
        mDownloadReceiver = new DownloadReceiver();
    }

    public void setUpdateListener(OnUpdateListener mUpdateListener) {
        this.mUpdateListener = mUpdateListener;
    }

    public void downloadApk(String apkUrl, String title, String desc) {
        // fix bug : 装不了新版本，在下载之前应该删除已有文件
        apkFile = new File(weakReference.get().getExternalFilesDir(Environment.DIRECTORY_DOWNLOADS), "app_name.apk");

        if (apkFile != null && apkFile.exists()) {
            apkFile.delete();
        }

        DownloadManager.Request request = new DownloadManager.Request(Uri.parse(apkUrl));
        //设置title
        request.setTitle(title);
        // 设置描述

        request.setDescription(desc);