Presentation of modal when clicking on tab bar item

Question

I am working (as an iOS developer) on an app, where there is a "Profile" tab, which doesn't have any content to show if the user isn't signed in.

The product owner wants to present a modal, when the user taps on the "Profile" tab, if the user isn't signed in. So instead of showing a "you can sign in" page as the tab bar content, he would like it presented as a modal over the tab bar and then keep the user on the previous tab, if the user closes the sign in modal.

As an experienced iOS user and developer this just feels wrong, but I am having a hard time arguing against it, because all I got is a very bad feeling.

I found this in the Apple HIG, but it doesn't really say anything about intercepting the tab bar item with another view:

Keep tabs visible even when their content is unavailable. If tabs are enabled in some cases but not in others, your app’s interface might appear unstable and unpredictable. When necessary, explain why a tab’s content is unavailable. For example, even when there is no music on an iOS device, the Listen Now tab in the Music app remains available and offers suggestions for downloading music.

I am starting to doubt whether I am on the right side of the best UX in this case.

Is it okay to present a modal when the user taps a tab bar item? If not, what are the arguments for it?

Answer 1

Giving the user (a sense of) control is a basic UX principle. When the user clicks the tab and never gets there, this is a major UX flaw. The user might even think it's broken. And it's not just annoying, it is also completely unnecessary: The tab seems to be a suitable space for the sign-in form. A modal blocks everything and takes up all screen space on a mobile device.

If you want to convince the product owner that it's a bad idea, show some websites that have cookie consent modals that pop up as soon as the page is loaded, just before you wanted to click a menu item. What most people do is close it as quickly as they can without actually seeing what they accepted or rejected. The reason is that it distracts from what they actually wanted to do while it is still freshly in their short term memory (losing that quickly). The goal was reaching the tab to see how signing in works or whatever, but users never reach the tab so the goal is missed and it is questionable if they accept the modal as their new goal (and don't care about the tab anymore). The sign-in modal may be meant to bring attention to creating an account but will probably result in the opposite and be ignored. To quote from nngroup.com:

Popup Content: Don’t Assume a Modal Overlay Will Deliver the Message

_{https://www.nngroup.com/articles/popups/}

Answer 2

I agree with you. Show a login opportunity on the tab, not in a modal. It's really about setting and meeting user expectations. Users know from experience (through convention) that they navigate to a different page/view using tabs, not triggering some kind of overlay/popup/modal. So there needs to be a really good reason to break conventions and thus user expectations.