从后台更新 UIProgressView

Question

I have a tab bar application with three tabs. In my second tab view i have a UIProgressView . I have a NSTimer in my viewDidLoad method which calls a method which updates the progressView

progressTimer = [NSTimer scheduledTimerWithTimeInterval:1.5 target:self selector:@selector(updateProgress) userInfo:nil repeats:YES];

All is fine so far.

I want to know how do i run the timer in the background throughout the lifecycle of the app, so that progressView is updated no matter which view the user is in. It will be great if you can show me with a code snippet.

Thanks in advance.

Answer 1

It's not advisable to update UI elements from background threads. Also, it's not advisable to modify UI elements of a view when the user is not in that view. You are using precious system resources.

Better way is to update the ProgressBar as soon as that view becomes active...

UPDATE : You can see here to know how to run a task in background thread. You could set up your NSTimer to start in the selector you specify there. But again, this kind of stuff could lead to some weird bugs. Better to avoid..

Answer 2

u can add the method in background this way

dispatch_async( dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
// Add code here to do background processing
// increment the progress here and keep the property of that count in appdelegate 
//
dispatch_async( dispatch_get_main_queue(), ^{
    // Add code here to update the UI/send notifications based on the
    // results of the background processing
});

});

in diffent view's viewWillAppear u can set this way: [loadingProgressView setProgress: appDelegate.count];

Answer 3

You could keep a property in the ProgressViewController (or even in the app delegate), say a float that tracks the progress. When you need to update the progress, another ViewController can change the value of the property.

Once the view becomes visible, update the UI ( UIProgressView ) from viewWillAppear: .