Alamofire履历未按预期工作

Question

I´m trying to download a file, and I want to detect when it loses connectivity using NetworkReachabilityManager like so:

self.reachabilityManager?.listener = { status in
        print("Status: \(status)")
        if status == .NotReachable {
            self.download?.suspend()
        }
        else if status == .Reachable(.EthernetOrWiFi) {
            self.download?.resume()
    }
    self.reachabilityManager?.startListening()

Initially I start the download like this:

self.download = self.manager.download(.GET, url) { (temporaryURL, response) -> NSURL in
        return NSURL(string: fullFilename)!
        }
        .progress { (bytesRead, totalBytesRead, totalBytesExpectedToRead) in
            self.setProgress(totalBytesRead, totalBytesExpectedToRead: totalBytesExpectedToRead)
        }
        .response { (request, response, data, error) in
            self.handleDownloadResponse(fullFilename, response: response, data: data, error: error)
    }

When I switch the network off, I would think that self.download?.suspend() would suspend the download request, and afterwards self.download?.resume() would restart the download, but the progress handler is never called, and after a while the response handler fires up with a timeout error

Should I be doing this differently? How can I achieve this behaviour (resume the download when network is restored)?

Answer 1

You need to make quite a few changes to this logic for things to work as intended. Here are a set of steps to get you where you want.

1. When you lose connectivity with the request in-flight, your response closure will be called and the error will indicate a connectivity issue.
2. In the response closure, if the data parameter is not nil , it is the resumeData of the download request and can be used to resume the download from where it left off.
3. If the data parameter is nil , then you'll need to restart the download since it can't be resumed.
4. In the connectivity closure, you only need to check the isReachable or isReachableOnEthernetOrWiFi parameters.
5. Inside the reachability check, you need to make a new download request with the resumeData if you have it, and a completely new request if you don't.

You cannot run the same download request again once the response closure has been called.

I haven't tried to use suspend and resume on download requests in the way you are. The docs do seem to imply that it's possible to use suspend and resume to do what you're doing, but the common practice is to cancel the request, then create a new one with the resume data. You'd also have to do it before the request would fail which I'm assuming is not possible.

I would guess that your requests have already failed by the time the reachability closure is called.

Hopefully that helps get you on the right track. For more information on any of those steps, I'd refer to the URL Loading System documentation along with the Alamofire README .