UPdate UIProgressView within for loop

Question

I've already searched for the problem, and the only hint was the performSelectorOnMainThread solution. I did that, but the view is not updating while the for loop is running. After the loop the progress value is displayed correctly – but that's not the point of an "Progress" View =)

The for loop is within a controller. I call a method to set the progress value:

CGFloat pr = 0.5; // this value is calculated
[self performSelectorOnMainThread:@selector(loadingProgress:) withObject:[NSNumber numberWithFloat:pr] waitUntilDone:NO];

And this is the loading progress method

-(void)loadingProgress:(NSNumber *)nProgress{
    NSLog(@"Set Progress to: %@", nProgress);
    [[self progress] setProgress:[nProgress floatValue]];
}

I also tried to put the method with the for loop into a background thread by using this at the top of the method:

    if([NSThread isMainThread]) {
        [self performSelectorInBackground:@selector(importData) withObject:nil];
        return;
    }
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

Maybe somebody can help me with this.

It's correct to let the loop run in another thread, and the way you seem to update the progress view also seems correct. Two questions: first, does your NSLog show that the correct values are set ? Second, are you sure that nothing else is blocking the main thread ? — DarkDust, May 25 '11 at 09:53
The NSLog-Messages are put out after the for-loop is done. The values are correct – but too late ;) – I'm not sure, that something else is blocking the main thread, but I can say, that I did nothing but displaying the view :) — cem, May 25 '11 at 09:57
Funny: The Log Messages are shown WHILE the for loop is running, the update to the UIProgressView is made AFTER the for loop was running. — cem, May 25 '11 at 10:08
The fact that you see the NSLog while the loop is running but the UI update afterwards smells like "main thread is blocked". You can easily check in your case: do `[self performSelectorOnMainThread:@selector(loadingProgress:) withObject:[NSNumber numberWithFloat:pr] waitUntilDone:YES];` (that's a `YES` instead of `NO`). If it doesn't come back then your main thread is blocked. The debugger will help you in this case. — DarkDust, May 25 '11 at 10:16
I don't know why, but after I gave up and worked on something else, the progress updates are working on my device. Voodoo =) — cem, May 25 '11 at 10:53

score 0 · Answer 1 · answered Feb 09 '12 at 11:50

0

 CGFloat pr = 0.5; // this value is calculated
[self performSelectorInBackground:@selector(loadingProgress:) withObject:[NSNumber numberWithFloat:pr]];

try this to set the progress value

answered Feb 09 '12 at 11:50

Satheesh

361
2
6
17

UI updates has to be done on the main thread. If you want to call the method "loadingProgress" on the background you must embed the setProgress in a block executed on the main thread which is meaningless. – foOg Jun 26 '13 at 14:05

UPdate UIProgressView within for loop

1 Answers1