How show activity-indicator when press button for upload next view or webview?

Question

when i click on button which title is click here to enlarge then i want show activity indicator on the first view and remove when load this view.

but i go back then it show activity indicator which is shown in this view.

in first vie .m file i have use this code for action.

-(IBAction)btnSelected:(id)sender{
UIButton *button = (UIButton *)sender;
int whichButton = button.tag;
NSLog(@"Current TAG: %i", whichButton);
UIActivityIndicatorView *spinner = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhiteLarge];
[spinner setCenter:CGPointMake(160,124)]; 
[self.view addSubview:spinner]; 
[spinner startAnimating];

if(whichButton==1)
{
    [spinner stopAnimating];

    first=[[FirstImage alloc]init];
    [self.navigationController pushViewController:first animated:YES];
    [spinner hidesWhenStopped ];

        }} 

in above code i have button action in which i call next view. Now i want show/display activity indicator when view upload. In next view i have a image view in which a image i upload i have declare an activity indicator which also not working. How do that?

Answer 1

Toro's suggestion offers a great explanation and solution, but I just wanted to offer up another way of achieving this, as this is how I do it.

As Toro said,

- (void) someFunction
{
    [activityIndicator startAnimation];

    // do computations ....

    [activityIndicator stopAnimation];  
}

The above code will not work because you do not give the UI time to update when you include the activityIndicator in your currently running function. So what I and many others do is break it up into a separate thread like so:

- (void) yourMainFunction {
    activityIndicator = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhiteLarge];

    [NSThread detachNewThreadSelector:@selector(threadStartAnimating) toTarget:self withObject:nil];

    //Your computations

    [activityIndicator stopAnimating];

}

- (void) threadStartAnimating {
    [activityIndicator startAnimating];
}

Good luck! -Karoly