One of the general principles of user interface design should be that when a user has to choose an option, it should be easily reversible – and it should be obvious how to do so.
Take a look at this grab, from Apple’s Keynote on iOS.
When I tapped on the button to insert an image, the iPad gave me the standard privacy control asking if I wanted to grant Keynote access to my photos. I accidentally hit “no”.
Now, whenever I open up the Photos control, I don’t see any images – but I do see an explanation of why I don’t see anything, and instructions on how to change that option if I wish.
That’s good design. It’s reversible, and it tells me how.
One of the ways you can tell that a piece of UI design really works is when you start trying to use it in other apps. A great example of this: Mr. Reader’s navigation buttons:
Those up, down and close buttons at the side aren’t there all the time. In fact, you have to slide your finger in from the edge of the screen to show it, and it’s your finger is positioned automatically over the “down” button. You have to hold and slide up or down to use one of the other buttons: if you lift your finger, the buttons disappear.
The nice thing is that you can do this from any part of the screen edge, so it doesn’t matter where your finger starts. I usually use my thumb, as I’m holding the iPad in portrait orientation.
It’s a lovely user interface device: hidden, yet easy to find and simple to understand. And it’s one of the things that makes Mr. Reader my favourite news reader on the iPad.