Objective-c – UIProgressView do not update in loop

objective cuiprogressview

I am loading a file and would like to show the progress in a UIProgressView. I can set the initial with:

[loadingProgressView setProgress: 0.00];

..in viewDidLoad this works perfectly.

The only thing I want to do then is to add 0.1 to the bar each loop but it does not update:

 while (eOF != 99999) {

    ...

    [loadingProgressView setProgress:loadingProgressView.progress + 0.10];

 }

I have checked around but not really found anything around just updating the bar each time I loop.

Anyone that can share some advice around this?

—UPDATE—

tried this without success:

while (eOF != 99999) {

    ...

    [loadingProgressView setProgress:loadingProgressView.progress + 0.10];
    [[NSRunLoop currentRunLoop] runUntilDate:[NSDate date]];

 }

Best Answer

You are looping through your while loop blocking the main thread, UI elements will not be able to refresh until the main thread becomes available. The best way around this is to run this code in a background thread (making the UI call on the main thread).

Or (I'm not sure about this one, see this discussion) you let the main thread some breathing space by calling

NSDate* futureDate = [NSDate dateWithTimeInterval:0.001 sinceDate:[NSDate date]];
[[NSRunLoop currentRunLoop] runUntilDate:futureDate];

Related Solutions

IPhone – Splash Screen with progress bar

As mentioned in another answer, for some finite amount of time, as your app is being launched, Default.png is displayed and you have no control over it. However, if in your AppDelegate, you create a new view that displays the same Default.png, you can create a seamless transition from the original Default.png to a view that you can add a progress bar to.

Now, presumably, you have created a view or similar and you are updating a progress bar every so often in order to give the user some feedback. The challenge here is that your view is only drawn when it gets called to do a drawRect. If, however, you go from AppDelegate to some initialization code to a viewcontroller's viewDidLoad, without the run loop getting a chance to figure out which views need to have drawRect called on, then your view will never display its status bar.

Therefore in order to accomplish what you want, you have to either make sure that drawRect gets called, such as by pushing off a lot of your initialization code into other threads or timer tasks, or you can force the drawing by calling drawRect yourself, after setting up contexts and such.

If you go with the background tasks, then make sure your initialization code is thread-safe.

SetProgress is no longer updating UIProgressView since iOS 5

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
}

Best Answer

Related Solutions

IPhone – Splash Screen with progress bar

SetProgress is no longer updating UIProgressView since iOS 5

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