MutableStateFlow not working with MutableList

user_5739402 0
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Here is my MutableStateFlow value I try to work with:

val songList: MutableStateFlow<MutableList<Song>> = MutableStateFlow(arrayListOf())

I need to observe changes (after methods like add, removeAt etc.) on my MutableList above but can't achieve that. My guess is since only the elements of the list change instead of the list itself, collect method doesn't get fired.

How can I achieve that using StateFlow if possible? If not, what is the correct way to do it?

Note that I need initial value of arrayListOf(), so LiveData probably won't be enough for me.

stateflow kotlin-stateflow android-livedata reactive-programming android
2 Answers

Solution:

  1. Create helper extension function:

    fun <T> List<T>.mapButReplace(targetItem: T, newItem: T) = map {
    if (it == targetItem) {
        newItem
    } else {
        it
    }
}

  2. React on action (ex: click event):

     val newStudent = student.copy(isSelected = !student.isSelected)

 viewModel.updateStudents(student, newStudent)

  3. Handle in ViewModel:

     fun updateStudents(currentStudent: Student, newStudent: Student) {
     val newList = _students.value.mapButReplace(currentStudent, newStudent)

     _students.value = newList
 }
user_34668080

For updating the MutableList inside the Stateflow, you have to map the item based on conditions like below, which I have accomplished, and it's performing nicely.

 _userList.value = _userList.value.map {
                if (it?.userName == updatedUser.userName) updatedUser
                else it
            }

Here _userList is a MutableStateFlow @Sam Sen's explanation assisted me a lot with my workaround solution.

user_46762910
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