setProgress is no longer updating UIProgressView since iOS 5

ios4, ios5, nsnumber, uiprogressview

Solution

I've seen a lot of questions like this one since the iOS 5 switch, and I'm not sure why there is a problem only in iOS 5. But mainly because I'm not sure why there wasn't a problem before.

In your code you call `[progressBar setProgress: [counterPercentage floatValue]];` from a background thread. This is a UI call and should not be made from a background thread. Also you call `setNeedsDisplay` which is not necessary to update the `progressBar` since an `UIProgressView` knows how to display itself. iOS 5 seems to have made the requirements for updating the UI more stringent, but only to the point of what are best practices anyway.

To my eye this looks like a perfect use for blocks. Using blocks your for loop could be written this way:

for ( pageDownload = 1; pageDownload < pagesToDownload; pageDownload++ ) {
        // Other stuff in background
    dispatch_async(dispatch_get_main_queue(), ^{
        progressBar.progress = ((float)pageDownload/(float)pagesToDownload);
    });
        // Other stuff in backgroud
}

Problem

I have a little trouble with a progress bar since iOS 5 came out. The code below was working fine before iOS 5 but with iOS 5 the progress bar is no longer displaying the new progress that is set within a loop. The code is expected to work like this: - Create the progress bar (works) - In a new background process: Set an initial progress of 0.25 (works) - In the same background process: Update the progress while going thru the loop (worked in iOS 4) Here's the code for the bar init: ``` // create a progress bar UIProgressView *progressBar = [[UIProgressView alloc] initWithFrame:CGRectMake(coverSizeX*0.25, coverSizeY - 34.0, coverSizeX*0.5, 9.0)]; progressBar.progress = 0.0; progressBar.progressViewStyle = UIProgressViewStyleBar; ``` and in a different thread it sets a starting point for the progress to 0.25: ``` // set an initial progress [progressBar setProgress: 0.25]; ``` a little later it is updating the progress within a loop to display the download progress: ``` // within a for-loop: NSNumber *counterPercentage; for ( pageDownload = 1; pageDownload < pagesToDownload; pageDownload++ ) { counterPercentage = [[NSNumber alloc] initWithFloat: (float)pageDownload / (float)((float)pagesToDownload)]; [progressBar setProgress: [counterPercentage floatValue]]; [progressBar performSelectorOnMainThread:@selector(setNeedsDisplay) withObject:nil waitUntilDone:YES]; } ``` … but the progress is not shown on the screen, the progress bar is stuck at the initial 0.25 progress that was set. Were there any changes with the iOS 5 release that could have broken it?

Original source