Modal vs non-modal views in iPhone

Question

I've been reading and looking at different iOS apps to design the UI for mine, and it feels like sometimes the difference between using a modal view or a non-modal view is not entirely clear... for example, from a "sign up" and "sign in" view, there are some apps that display the sign in form in a modal view, an another do navigating to the view in the "right" (appearing then the "back" button). What should be the best way, from the point of view of user experience? Since a modal view for iPhone occupies the entire screen, there is another difference between modal and non-modal views apart from one sliding up from the botton, and the other one sliding left from the right?

Also, is it correct (and possible) to navigate through several views from a modal view displaying a back button in the navigation bar, or it should not be that way and a modal view should always display cancel and complete buttons (not a back button)?

Maybe I made a lot of questions... thanks in advance!

Answer 1

Given your question is specific to Apple iOS I will refer to the Human Interface Guidelines (HIG):

Use a modal view when you need to offer the ability to accomplish a self-contained task related to your app’s primary function. A modal view is especially appropriate for a multistep subtask that requires UI elements that don’t belong in the main app user interface all the time. Which is very similar to Michael's first paragraph.

Further:

A navigation bar enables navigation through an information hierarchy and, optionally, management of screen contents.

As such, you can have a navigation hierarchy when presenting a modal view. The modal, to try and sum it up, is a way to step out of the normal flow of the app so the user can accomplish something prior to continuing on their way. In the example of a login screen, it makes more sense (based on the HIG), to present it modally, then dismiss it to return the user to the view from whence they came.

For example, go to the Settings app -> Mail -> Add new account (all presented via a navigation hierarchy) - choose one of the providers and a "login page" is presented, modally. Once you fill it out and the whole thing is confirmed, the modal disappears and you are back to your account list. Another example is in the Calendar app, when you add an event, which takes you out of the process of viewing events, the view is presented modally - when you go to assign a calendar, however, the view is presented hierarchically.

When reviewing apps for "how should I do this" - I typically look to those apps created by Apple first, not other developers, because many of us (the royal us) tend to neglect things like the HIG and Apple recommendations; however, Apple tends to be pretty consistent.

To try and encapsulate all of that succinctly. Read the HIG; memorize it; print it out and, if after a few months it's not heavily worn, something is wrong (that's a paraphrase from Apple). When looking to other apps for "advice" on how to handle certain interactions, look at the apps created by Apple first, because they pretty much follow the HIG - and, there are a variety of experiences used not just the standard UI elements.

Hope that helps.

RE: The follow-up question in the Comments

There isn't anything in the HIG that reccomends anything regarding modals inside of modals; however, if you look at the Contacts app, you see the following:

1. Add a contact (presents modal),
2. Choose add photo (presents action sheet) to either take a photo or choose from your library,
3. Either option will present another modal (the Camera app or the Photo Library portion of the Photos app, respectively).

So, assuming Apple adheres to their own UX philosophies, then the answer would appear that it is okay to have multiple modals presented over time; so long as canceling or saving from all of them will lead the user back to the start of the flow.

Answer 2

I would say that the primary reason for using a modal view is for a user to complete a single task that they should not be interrupted from. This means that all the information required for the user to complete the task should be contained within the modal window it self, because the behaviour for a modal window is designed such that they cannot access other parts of the screen while they are in the modal window (unless they cancel or exit from it).

From a user's perspective, it means that modal windows should not be used for long tasks because the longer you occupy the user's sole focus, the more likely they will want to do something else. To ensure that they can complete the task defined in the modal window successfully and without interruption you should make this as short as possible.

I suggest having a look at a couple of references and examples to get the idea, and then if you have other questions just post some specific questions.

Modal Windows

Examples