如何使用实时数据更新回收者视图的 textView

Question

I want to update a textview of the recycler view with a live data.
how can I do this? I am a beginner please help

this is my viewModel class

class ViewModelClass : ViewModel() {
    var rating = MutableLiveData<String>("NA")
}

I have a textView in a recycler view which I want to update after taking the text from the edit text but I could not do this because I can not get the reference of that textview in the MainActivity.

btnSave.setOnClickListener {
            val rating : String = etRating.text.toString()
            viewModel.rating.value = rating
        }

Answer 1

Follow these steps:

1. Create an adapter to configure your recyclerview. Make sure to implement de DiffUtils correctly.

class MyAdapter: ListAdapter<String, MyAdapter.MyAdapterViewHolder>(DIFF_CALLBACK) {

    class MyAdapterViewHolder(
        private val binding: ItemSimplePosterBinding
    ): RecyclerView.ViewHolder(binding.root) {
       // implementation here
    }

    companion object {
        private val DIFF_CALLBACK = object : DiffUtil.ItemCallback<String>() {
            override fun areItemsTheSame(oldItem: String, newItem: String): Boolean {
                // need a unique identifier to have sure they are the same item. could be a comparison of ids. In this case, that is just a list of strings just compare like this below
                return oldItem == newItem
            }

            override fun areContentsTheSame(oldItem: String, newItem: String): Boolean {
                // compare the objects
                return oldItem == newItem
            }

        }
    }
}

2. On your ViewModel, create a function that will add the new rating to your list:

class MyViewModel: ViewModel() {

    private val _rating = MutableLiveData<List<String>>(emptyList())
    val rating: LiveData<List<String>>
        get() = _rating

    // implement a function that adds a new item on the rating list
    fun addRating(newRate: String) {
        val newList = mutableListOf<String>()
        _rating.value?.let { newList.addAll(it) }
        newList.add(newRate)
        _rating.value = newList
    }
}

See that I didn't expose the mutableLiveData, always pay attention to following this best practice to let private the mutableLiveData and let public just the immutable live data.

3. Then, the last step is to observe the live data changes. So, when the list change on viewmodel, you will receive the updated list on the observer just submit the list for adapter:

class MyFragment: Fragment()  {

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)

        // set the adapter to your recycler view
        // observe changes of your live data
        viewModel.rating.observe(viewLifecycleOwner) { ratings ->
            adapter.submitList(ratings)
        }
    }
}