Also, if content is not found, its more of a server side that you need to account for as well. How would I inspect the bytes for the headers?
Also i'm ok with downloading it all and then looking at the headers. I am storing them in a caches directory so would it be best to read from an nsurl to see the headers? Again, should there not be a mechanism on the server side to ensure the media content is validated and stored prior to attempting to download?
Are you making REST api requests to some backend - php or similar? Please include the vital information for others. Thanks for the help I got it figured out! Add a comment. Active Oldest Votes. Improve this answer. Leo Dabus Leo Dabus k 55 55 gold badges silver badges bronze badges. Pratik Sodha Pratik Sodha 3, 2 2 gold badges 17 17 silver badges 35 35 bronze badges. Sign up or log in Sign up using Google. Sign up using Facebook. You can send messages to the subscriber by calling various receive methods on it.
You have to manually send the completion event with the. Also we have to move the downloaded temporary file before the completion block returns otherwise we'll completely lose it. This time I'm going to simply move the file to the application cache directory. As a gratis cancellation is a great way to end battery draining operations. You just need to implement a custom cancel method. Let's say that there are 4 kinds of subscriptions.
You can use the. If you choose this path you can use the. You can also subscribe a subject. The subscriber above will simply print out the incoming values. We have to be extremely careful with memory management. The received subscription will be stored as a strong property, but when the publisher sends a completion event we should cancel the subscription and remove the reference.
When a value arrives we have to return a demand. In our case it really doesn't matter since we'll only have 1 incoming value, but if you'd like to limit your publisher, you can use e. I promised a working image downloader, so let me explain the whole flow. We have a custom download task publisher that'll save our remove image file locally and returns a tuple with the file url and the response. Next I'm going to simply assume that there was a valid image behind the url, and the server returned a valid response, so I'm going to map the publisher's output to an UIImage object.
I'm also going to replace any kind of error with a fallback image value. In a real-world application, you should always do some extra checkings on the URLResponse object, but for the sake of simplicity I'll skip that for now. The last thing is to update our image view with the returned image. Since this is a UI task it should happen on the main thread, so we have to use the receive on: operation to switch context.
If you want to learn more about schedulers in the Combine framework you should read Vadim Bulavin 's article. It's a gem. If you are not receiving values on certain appleOS versions, that's might because there was a change in Combine around December, You should check these links: link1 , link2. Finally, we can display our image.
Ouch, but wait What about caching? What happens if I want to use the image in a list, shouldn't I cancel the download tasks when the user scrolls? Maybe I'll write about these issues in an upcoming tutorial, but I think this is the point where I should end this article.
If you force-quit the app by swiping up from the app switcher the system cancels all background tasks:. If the app is suspended the app process is terminated while a download is still in progress and then started again, if the download is still active, you can access the URLSession with the same identifier and it will resume notifications about the progress of the download.
But, if a task is finished while the app is not running, the system will launch the app in the background and call the AppDelegate method handleEventsForBackgroundURLSession.
This is the only chance to get notified about such a download:. This can be tricky to debug.
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