Android：当用户在导航组件、单活动应用程序中点击片段 B 时更新片段 A

Question

I have the following requirement: Fragment A shows all referred friends from API call, which it calls onCreateView. The user can navigate from Fragment A -> Fragment B. In Fragment B the user can refer new friends. When the user refers a friend I make an API call and trigger activity.onBackPressed() to pop Back to Fragment A.

On return in Fragment A, I need to make the API call to get all referred friends to update the UI. Unfortunately neither onCreateView() nor onResume() nor onStart() are called when I pop back. How do I make the new API call and update the UI?

Fragment A:

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
 super.onViewCreated(view, savedInstanceState)
viewModel = ViewModelProvider(this).get(ReferAFriendViewModel::class.java)

viewModel.getRAFStatus().observe(viewLifecycleOwner,{
    //UpdateUI
})

}

Fragment B:

viewModel.postSendInvites(binding.etName.text.toString(), binding.etEmail.text.toString())

requireActivity().onBackPressed()

Answer 1

You can use this in your first fragment.

findNavController().currentBackStackEntry?.savedStateHandle?.getLiveData<Type>("key")?.observe(
    viewLifecycleOwner) {result ->
    // Do something with the result.
}

And in your second fragment.

findNavController().previousBackStackEntry?.savedStateHandle?.set("key", result)

I end up creating two extension functions for it.

fun <T> Fragment.getCurrentBackStackEntryLiveData(key: String): MutableLiveData<T>? {
    return findNavController().currentBackStackEntry?.savedStateHandle?.getLiveData(key)
}

fun <T> Fragment.setCurrentBackStackEntryLiveData(key: String, value: T) {
    findNavController().previousBackStackEntry?.savedStateHandle?.set(key, value)
}

Here is the link for the same.

Answer 2

Use MVVM and SharedViewModel. see this link for more information.