How to model cross fragment transaction (ongoing process) in Android MVVM application?

Question

I am developing an app that has some ongoing process that almost all screens depend on. Let's call it ActiveTransaction. So, one fragment prepares items, the other fragment prepares payment, another adds discounts, etc... If one part fails, everything needs to rollback.

So, basically, I need to achieve atomicity across multiple fragments. I've tried to use shared ViewModel for this, but since each fragment adds its own stuff, that shared ViewModel has become too big.

So, I wonder what would be the best way to handle those processes that stretch over multiple fragments. Should I have perhaps a singleton object ActiveTransaction that is injected in each viewModel? Is this maybe what other technologies call the app State?

I haven't found anything in the MVVM architecture guidelines.

Answer 1

You can create Tabbed Activity - blank Activity with tabs. New project -> Tabbed Activity.

You will have one activity and multiple fragments. So all functionality will be in MainActivity. Your fragments will contain views, which will call methods from MainActivity. All objects and calculations will be in main activity, so if it fails (because of memory lack), everything will collapse too.

For Example:

You have one Tabbed activity MainActivity and 3 fragments: Item Fragment, PaymentFragment and DiscountFragment. MainActivity contains multiple methods, let's say prepareItems(), preparePayment(), addDiscount(). User can go through Tabs, opening fragments. MainActivity methods can be called only via fragments. So if MainActivity collapses, the whole process will collapse.

So you will achieve atomicity and user can see changes by going through tabs. You can replace Tabs Activity by other scenario with single activity and multiple fragments which don't have functionality but contain views which will call methods from MainActivity