You need to ask the OS to keep the app running, it has nothing to do with Dropbox... When you start uploading, do this:
UIBackgroundTaskIdentifier bgTask = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{
[[UIApplication sharedApplication] endBackgroundTask:bgTask];
}];
... and store the bgTask
somewhere. Then when your upload completes or fails, do this:
[[UIApplication sharedApplication] endBackgroundTask:bgTask];
That will tell the OS to keep your app running because there's a background task running...
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