Question

I have an app with Tab Bar.
Each Tab starts to request some data from the Internet using NSURLConnection way once is loaded.
Everything works fine, but if I switch tab when data is still loading, then the first request is “queued” to the second one and I found my data duplicated.
How can I suspend the download of the data when the user switches tabs?

Answer 1

There is no direct built-in support to pause an NSURLConnection. Instead, you need to:

1. Cancel the connection
2. Store the data received so far
3. To resume, start a new connection that requests to receive data starting from where it left off
4. Append incoming data to that already received

It’s best to check that the data on the server hasn’t changed in the meantime too, and that data in step 4 is the bit of file you requested.

Alternatively, it may be enough to unschedule the connection from the runloop. This should make it resumable (by rescheduling) within a small timeframe, but will fail if left too long.