Programming iOS 6, 3rd Edition

UIActivityIndicatorView

An activity indicator (UIActivityIndicatorView) appears as the spokes of a small wheel. You set the spokes spinning with startAnimating, giving the user a sense that some time-consuming process is taking place. You stop the spinning with stopAnimating. If the activity indicator’s hidesWhenStopped is YES (the default), it is visible only while spinning.

An activity indicator comes in a style, its activityIndicatorViewStyle; if it is created in code, you’ll set its style with initWithActivityIndicatorStyle:. Your choices are:

• UIActivityIndicatorViewStyleWhiteLarge
• UIActivityIndicatorViewStyleWhite
• UIActivityIndicatorViewStyleGray

An activity indicator has a standard size, which depends on its style. Changing its size in code changes the size of the view, but not the size of the spokes. For bigger spokes, you can resort to a scale transform.

You can assign an activity indicator a color; this overrides the color assigned through the style. An activity indicator is a UIView, so you can set its backgroundColor; a nice effect is to give an activity indicator a contrasting background color and to round its corners by way of the view’s layer (Figure 25-1):

self.activity.color = [UIColor yellowColor];
self.activity.backgroundColor = [UIColor colorWithWhite:0.2 alpha:0.4];
self.activity.layer.cornerRadius = 10;
CGRect f = self.activity.bounds;
f.size.width += 10;
f.size.height += 10;
self.activity.bounds = f;

Figure 25-1. A large activity indicator

Here’s some code from ...