Question

I’m downloading some pictures and have created a progress bar. I’m using asynchronous mode with NSURLConnection and initiate about 15 pictures downloads at the same time. During the initiation i call didStartLoadImages and the bar is successfully set to 0 width on the screen.

Now the problem start, when one of the images is completed it will call didLoadImageWithTotalPercentCompleted: and update the bar with the current percent. It works perfectly and the logs write nicely Updating frame to: 20% etc.. But the User Interface doesn’t update UNTILL all the images are completed?

I just notice that the main thread is blocked even tho it’s asynchronous?

Connection.m

-(void)loadImage:(NSString*)imageName numberOfImagesInSecquence:(int)nrOfImages {
    NSString *url = [NSString stringWithFormat:@"https://xxx.xxx.xxx.xxx/~%@/files/%@",site,imageName];

    /* Send URL */
    NSURL *urlToSend = [[NSURL alloc] initWithString:url];
    NSURLRequest *urlRequest = [NSURLRequest requestWithURL:urlToSend];
    theConnection = [[NSURLConnection alloc] initWithRequest:urlRequest delegate:self startImmediately:YES];

    self.receivedData = [NSMutableData data];
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
    connectionIsLoading = NO;
    [[self delegate] didLoadImagesWithProcent:((float)1 - ((float)[imageArray count] / (float)nrOfImages)) *(float)100];
}

MainViewController.m

-(void)didStartLoadImages {
     /* Sets progress bar to 0% */
     [progressBar setBarWithPercent:0];
}


-(void)didLoadImageWithTotalPercentCompleted:(int)percent {
    if (percent == 100) {
        /* Done */
    } else {
        [progressBar setBarWithPercent:percent];
    }
}

ProgressBar.m

-(void)setBarWithPercent:(float)percent {
    int maxSizeOfBar = 411;

    [UIView beginAnimations:@"in" context:NULL];
    [UIView setAnimationDuration:0.2];
    [UIView setAnimationCurve:UIViewAnimationCurveEaseInOut];
    [UIView setAnimationBeginsFromCurrentState:YES];

    CGRect frame = bar.frame;
    frame.size.width = maxSizeOfBar * (percent / 100) + 10;
    bar.frame = frame;
    NSLog(@"Updating frame to: %i",percent);

    [UIView commitAnimations];

}

Answer 1

This may be a problem with integer math truncation. Change your percentage value to a float or CGFloat instead of an int, and for all of your numbers write them like 100.0f instead of 100 to force C to treat them as floats instead of integers.

Basically, in C if you do 1/2 it doesn’t give you 0.5, it gives you 0 because it uses integer math, and 2 doesn’t go into 1 a whole number of times. So when calculating a percentage, you really want to use floats because (1/100) * x will always be zero, but (1.0f/100.0f) * x will work correctly.