Why isn't it common to swipe between top-level views when we use a bottom navigation?

Question

It’s a common pattern on Android that if you have a tabs, you can swipe between top-level views. Google introduced the bottom navigation a while ago, which we already know from iOS. How come it isn’t common that a swipe lets me switch between top-level views when a bottom navigation is used?

For example:

• Twitter and Facebook on Android use tabs. I can switch between top-level views by swiping.
• Twitter and Facebook on iOS use a bottom navigation. I can’t switch between top-level views by swiping.
• Google+ on Android and iOS use a bottom navigation. I can’t switch between top-level views by swiping.

For this question, let's ignore two obvious things, since they're not always present:

1. that top-level views can contain elements like carousels.
2. that an app with a bottom navigation can also have tabs.

I can imagine it evolved this way on Android because tabs are more difficult to reach than a bottom navigation. To solve this, we let the user swipe horizontal and accept any usability issues if the top-level view contains any horizontal scroll elements. But this doesn't explain why we can switch top-level views right now.

Another argument for iOS could be that there is already a horizontal swipe gesture to make you go back. This makes it harder for a user to differentiate between 'I want to go back' and 'I want to go that way'. I believe most Android devices still have a hardware button to solve this issue. But that would still leave the behavior on Android into the open

Answer 1

I think that this mainly refers to some convention rather than a specific reason. When searching for a specific reason, though, the only thing I could think of was that the top navigation, even by its name, refers to something on top. However, I admit this is a really weak reason, as bottom nav also defines the main sections of the app.

Therefore, while answers with some reasonable argumentation for it can be formed, I believe this is just a convention assumed and followed by a platform visual language.

However, there is one really reasonable answer here, even though referring to just a part of the question. The tabs on top are swipeable because they are harder to tap (whereas the bottom ones are easier to access with the thumb). Hence, this action has apparently been reserved to support switching between the top, inaccessible for the thumb elements, leaving tap for the more accessible bottom ones - because for them it barely matters whether they are tapped or swiped.

The swipe itself, by the way, conveys more than switching views, because it can also refer to some actions performed on the items themselves. This is a long war, though, with no clear winner at the moment.

Answer 2

Bottom navigation appeared much later in the material design guidelines than tabs and it serves a slightly different purpose.

From the Material guidelines on navigation:

Tabs

Tabs allow users to quickly move between a small number of equally important views.

Bottom navigation

A bottom navigation bar allows users to quickly move between a small number of top-level views.

Bottom navigation is a replacement for the navigation drawer when the number of elements is small. At larger sizes, the material guidelines recommend transitioning from bottom navigation to side navigation.

Not allowing swiping between elements in bottom navigation:

1. Allows combining bottom navigation and tabs (which is perfectly valid according to the guidelines)
2. Maintains consistency in behavior between apps that only use bottom navigation and apps that use both tabs and bottom navigation
3. Maintains consistency when transitioning from a small window size with bottom navigation to a larger window size with a navigation drawer. (As you also can't swipe between navigation drawer elements)
4. Maintains consistency with iOS, where bottom navigation acts the same way.