How to set progress in UIProgressView

Question

I have a problem calculating progress for my UIProgressView. My float value has no effect on the progress. I tried to set progress manually it works fine but if I try to calculate it it doesn't work.

Here is my code :

- (void) initProgressbar {

   self.progressView = [[UIProgressView alloc] initWithProgressViewStyle:UIProgressViewStyleDefault];
   [self.progressView setFrame:CGRectMake(0, 0, SCREEN_WIDTH / 2, 10)];
   self.progressView.center = CGPointMake(SCREEN_WIDTH - 110, SCREEN_HEIGHT - 25);
   self.progressView.progress = 0.0;
   [self.view addSubview:self.progressView];
}

nbElementsSync and nbElementsToSync are global int properties and nbElementsSync is incremented by a loop before updateProgress method is being called.

MyController.h

@interface MyController : UIViewController {

   NSString *json;
   int nbElementsToSync;
   int nbElementsSync;

}

@property (nonatomic, strong) UIProgressView *progressView;

MyController.m

nbElementsSync = 0; // Nb elements synchronized
nbElementsToSync = [[json valueForKey:@"count"] intValue]; // Nb elements to synchronize

for (NSString* result in results) {

    nbElementsSync++;
    [self updateProgress];

}

And here is my method to set up the progress :

- (void) updateProgress {

   [self.progressView setProgress:((float)nbElementsSync / nbElementsToSync)];
   NSLog(@"percent : %f", ((float)nbElementsSync / nbElementsToSync));

}

Results of my NSLog :

percent : 0.003937
percent : 0.007874
percent : 0.011811
percent : 0.015748
percent : 0.019685
percent : 0.023622
...

Any idea to solve it ? Thanks in advance.

Answer 1

Have you tried doing the loop in a background process, not to block the UI updates :

MyController.m

Call this where you need to:

[self performSelectorInBackground:@selector(syncInBackground) withObject:nil];

Then

- (void)syncInBackground
{
    int nbElementsSync = 0; // Nb elements synchronized
    int nbElementsToSync = [[json valueForKey:@"count"] intValue]; // Nb elements to synchronize

    for (NSString* result in results) {
        nbElementsSync++;

        float percent = (float)nbElementsSync / nbElementsToSync;

        [self performSelectorOnMainThread:@selector(updateProgress:) withObject:[NSNumber numberWithFloat:percent] waitUntilDone:NO];
    }   
}

- (void) updateProgress:(NSNumber *)percent {

    [self.progressView setProgress:percent.floatValue];
}