使用 MVVM 导航到其他片段时，recyclerview 中的列表会重复

Question

当导航到其他片段并返回片段时，recyclerview 中的列表内容会重复。

当用户点击项目并导航回同一片段时，recyclerview 会重复

视图模型：

    private var listMutableLiveData: MutableLiveData<ArrayList<OffersModelClass>> =
    MutableLiveData()  

    var arrayListMainUI: ArrayList<OffersModelClass> = ArrayList()

    val listLiveData: LiveData<ArrayList<OffersModelClass>>
        get() = listMutableLiveData
    

    fun loadData(reload: Boolean) {
    if (reload) {
        databaseReference.addValueEventListener(object : ValueEventListener {
            override fun onDataChange(snapshot: DataSnapshot) {
                for (data in snapshot.children) {

                    val model = data.getValue(OffersModelClass::class.java)

                    //Getting the offer ID to load its images
                    val imageID: String = model?.imageID.toString()

                    val fileRef11 = FirebaseStorage.getInstance().reference.child(
                        "offers/$imageID.jpg"
                    )
                    fileRef11.downloadUrl.addOnSuccessListener { uri ->

                        //Assigning the image uri and converting it to string
                        model?.ImageUri = uri.toString()

                        //Assigning the new time format
                        model?.Time = model?.Time?.let { calculateTimeAge(it) }

                        //Adding the data to arraylist as whole to observe it from the fragment
                        arrayListMainUI.add(model as OffersModelClass)
                        listMutableLiveData.postValue(arrayListMainUI)

                    }
                }

            }

            override fun onCancelled(error: DatabaseError) {
                TODO("Not yet implemented")
            }
        })
    }
}

片段：

    recyclerView.layoutManager = LinearLayoutManager(context)
    recyclerView.setHasFixedSize(true)

    viewModel = ViewModelProvider(requireActivity()).get(ViewModel::class.java) 

     if (user != null) {
        // User is signed in
         viewModel.loadData(true)
       
    }
    viewModel.listLiveData.observe(viewLifecycleOwner, { arrayList ->
        offerAdapter = OfferAdapter(arrayList)
        recyclerView.adapter = offerAdapter
        offerAdapter.notifyDataSetChanged()
    })

Answer 1

在 onDataChanged 之前调用 arrayListMainUI.clear() for (data in snapshot.children)。为什么这会起作用？ 答案： 当您导航回片段时，您并没有创建 arrayListMainUI 的另一个实例。因此，以前的数据不会被清除，新的数据会与以前的数据一起添加，从而创建重复列表。

使用 MVVM 导航到其他片段时，recyclerview 中的列表会重复

The list in recyclerview is getting duplicated when navigating to other fragment with MVVM

android

mvvm

kotlin

android-recyclerview