How to get fraction of the progress completed in On Demand Resource download?

Question

I want to get the progress in fractions but what I get is 0 at the beginning of the request and 1 at the end of the download. Here is the code I have written

    [self.resourceRequest.progress addObserver:self forKeyPath:@"fractionCompleted" options:NSKeyValueObservingOptionNew context:@"observeForrestLoad"];

    - (void)observeValueForKeyPath:(nullable NSString *)keyPath ofObject:(nullable id)object change:(nullable NSDictionary *)change context:(nullable void *)context {
            if((object == self.resourceRequest.progress) && [keyPath isEqualToString:@"fractionCompleted"]) {
            // Do something with self.resourceRequest.progress.fractionCompleted
           NSLog(@"progress= %f",self.resourceRequest.progress.fractionCompleted);

    }
 }

Can anyone tell how do I get the progress determinately in fractions?