如何在iOS上的按钮操作上显示忙碌指示器？

Question

I want to start busy indicator on button action, I use following code in IB action as:

 busyIndicator = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray];
 busyIndicator.center = self.view.center;
 [busyIndicator setColor:[UIColor redColor]];
 [self.btnInjuryPrevention addSubview:busyIndicator];
 [self.view addSubview:busyIndicator]; // spinner is not visible until started

[busyIndicator startAnimating];
if(![AppStatus isAppOnline]) {
    noInternetViewController = [[NoInternetViewController alloc] initWithNibName:@"NoInternetViewController" bundle:[NSBundle mainBundle]];
    noInternetViewController.view.tag = CHILD_CONTROLLER_TAG;
    [self.navigationController pushViewController:noInternetViewController animated:YES];
    NSLog(@"Yoy are offline..>!!");
}
else
{
    mInjuryPreventionViewController=[[InjuryPreventionViewController alloc] initWithNibName:@"InjuryPreventionViewController" bundle:nil withHeader:@" Injury Prevention" withId:INJURY_PREVENTION_ID];
    mInjuryPreventionViewController.view.tag = CHILD_CONTROLLER_TAG;
    [self.navigationController pushViewController:mInjuryPreventionViewController animated:YES];
    //[mInjuryPreventionViewController release];
}
// [self removeLoadingView];
[busyIndicator stopAnimating];

I use above code, but busy indicator will not start, So can you tell me it is possible?

Answer 1

If you start and stop an animation in a single block, you won't see anything. You can think of the startAnimating method to mean "start animating when control returns to the OS."

It's not clear why you need a spinner there. Does creating the view controller take a long time? Still, if you move the view controller stuff into a new method you could do something like:

...
// create busy indicator
[busyIndicator startAnimating];
[self performSelector:@selector(createViewController) withObject:nil afterDelay:0]; 

...

// at the end of the createViewController method...
[busyIndicator stopAnimating];

Answer 2

as i understand from your given code firstly you are on some UIViewController and where you are adding your UIActivityIndicatorView and after all you making two condition if-else where you initializing two other UIViewController so in this view(Generated after if-else) how your UIActivityIndicatorView will show as you added it as

    [self.view addSubview:busyIndicator]; // spinner is not visible until started

please define your function executing with if statement.?

Keep Coding

Answer 3

As you are starting and stoping the busuIndecator in a single method, without any long processing, so both function executes within milisecons so you are not able to see the busyIndecator on UI. To show a busyIndecator or any outlet on UI. there should me some time span which is human recognisable. Like:

[busyIndicator startAnimating];
//Do EXTREME PROCESSING!!!
[busyIndicator stopAnimating];