BGAUpgradeUtil.getDownloadProgressEventObservable()
        .compose(this.<BGADownloadProgressEvent>bindToLifecycle())
        .subscribe(new Action1<BGADownloadProgressEvent>() {
            @Override
            public void call(BGADownloadProgressEvent downloadProgressEvent) {
                if (mDownloadingDialog != null && mDownloadingDialog.isShowing() && downloadProgressEvent.isNotDownloadFinished()) {
                    mDownloadingDialog.setProgress(downloadProgressEvent.getProgress(), downloadProgressEvent.getTotal());
                }
            }
        });

@AfterPermissionGranted(RC_PERMISSION_DOWNLOAD)
public void downloadApkFile() {
    String[] perms = {Manifest.permission.WRITE_EXTERNAL_STORAGE};
    if (EasyPermissions.hasPermissions(this, perms)) {
        // 如果新版 apk 文件已经下载过了，直接 return，此时不需要开发者调用安装 apk 文件的方法，在 isApkFileDownloaded 里已经调用了安装」
        if (BGAUpgradeUtil.isApkFileDownloaded(mNewVersion)) {
            return;
        }

        // 下载新版 apk 文件
        BGAUpgradeUtil.downloadApkFile(mApkUrl, mNewVersion)
                .subscribe(new Subscriber<File>() {
                    @Override
                    public void onStart() {
                        showDownloadingDialog();
                    }

                    @Override
                    public void onCompleted() {
                        dismissDownloadingDialog();
                    }

                    @Override
                    public void onError(Throwable e) {
                        dismissDownloadingDialog();
                    }

                    @Override
                    public void onNext(File apkFile) {
                        if (apkFile != null) {
                            BGAUpgradeUtil.installApk(apkFile);
                        }
                    }
                });
    } else {
        EasyPermissions.requestPermissions(this, "使用 BGAUpdateDemo 需要授权读写外部存储权限!", RC_PERMISSION_DOWNLOAD, perms);
    }
}