Resuming download after restart application about downloader

[Toqe]

Please have a look at issue #2.

Basically you need to access the AlreadyDownloadedRanges property of the MultiPartDownload object you are using. You can for example serialize this to a file when closing your application. On Restart just deserialize it and provide it to the constructor of MultiPartDownload.

[Dolus1984]

I already saw issue #2
I suspected that it can be done by serialization and deserialization,
Sadly there are unexpected behaviors which may prevent you using such method by users like unexpected shutdown, so your serialized object does not fit with file content if i am right.
It would be good to use AddRange but i believe it does not really fit with your multi-part concept.
I previously used java based app (JDownloader) which was capable to resume multi-part downloading after restarting app.

[Toqe]

I'm not quite sure if I understand your point correctly, but I think events like sudden shutdown could be handled by not only saving the state of a download when stopping it gracefully, but also saving it from time to time. It's also no problem if the saved state is a bit older than the already downloaded file, as the resumed download would only overwrite some already downloaded parts which causes not trouble.

If you really want to be sure that the download on the disk is matching the state of the already downloaded parts, you could write your own version of DownloadToFileSaver, which stores the state to a file placed beside the target file as soon as DataReceived is called. Drawback of this solution would be additional disk throughput, so you may have to throttle the writes of the state to disk.

[Dolus1984]

You are right, i missed that already downloaded parts will be overwritten.
I properly deserialized AlreadyDownloadedRanges to file and serialized it back, so it resumed much faster than by AddRange request.
Thank you for this suggestion.