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?