NSProgress/UIProgressView example

progress.m

// Create a progress bar view
UIProgressView *progressView = [[UIProgressView alloc] initWithProgressViewStyle:UIProgressViewStyleBar];
progressView.progress = 0;

// Assume we have a progress object
NSProgress *progress = [self progressForOngoingTask];

// Observe the 'fractionCompleted' property and update the progress view as it changes
[self.KVOController observe:progress keyPath:@"fractionCompleted" options:NSKeyValueObservingOptionNew block:^(id _Nullable observer, id _Nonnull object, NSDictionary<NSString *, id> *_Nonnull change) {
    dispatch_async(dispatch_get_main_queue(), ^{
        progressView.progress = progress.fractionCompleted;
    });
}];

user-info.m

// Observe a child NSProgress object's userInfo property and update the parent's userInfo as it changes
[self.KVOController observe:childProgress keyPath:@"userInfo" options:NSKeyValueObservingOptionNew block:^(id _Nullable observer, NSProgress * _Nonnull childProgress, NSDictionary<NSString *, id> *_Nonnull change) {
    [parentProgress setUserInfoObject:childProgress.userInfo[@"notesDownloaded"] forKey:@"notesDownloaded"];
    [parentProgress setUserInfoObject:childProgress.userInfo[@"totalNotesToDownload"] forKey:@"totalNotesToDownload"];
}];