Question

I want to display a progress indicator in a semi-transparent box that floats over a table view. In other words, when the table contents are being downloaded, I want an ‘Updating’ label to appear over it.

I have seen this in several apps in the store, notably Facebook (when you shake to reload) and Darkslide.

My first impulse is to create a semi-transparent UIView, place a UILabel and a UIProgressIndicatorView inside it, and add it to the view hierarchy… but where? A UIView may not overlap its siblings, so I can’t make it a subview of the window. I also can’t make it a subview of the table, because then it will scroll up and down with the table content.

I thought about creating a new UIWindow, but the documentation basically says don’t.

I know CALayers can overlap each other, so that would be an option, but I can’t put a progress indicator inside a CALayer, can I? Should I roll my own progress indicator that animates a CALayer instead of a UIView?

I’m not interested in hearing about private APIs.

Edit: The question was based on a faulty assumption. NSViews (on Mac OS X) may not overlap, but UIViews on the iPhone may.

Answer 1

You can definitely overlap views. Just add the transparent overlay as a subview in the tableView.

From UIView’s documentation:

UIView objects are arranged within an UIWindow object, in a nested hierarchy of subviews. Parent objects in the view hierarchy are called superviews, and children are called subviews. A view object claims a rectangular region of its enclosing superview, is responsible for all drawing within that region, and is eligible to receive events occurring in it as well. Sibling views are able to overlap without any issues, allowing complex view placement.